LASER VISION CORRECTION

INTRODUCTION

Medical professionals differ in their interpretation of the facts as presented on youreyesite.com.  This article is for informational purposes only.  Be sure to check with your physician in order to determine their opinion on the risks, rewards, potential outcomes and options available to you while you determine whether laser vision correction is right for you.

HOW LASER EYE SURGERY WORKS: A Basic introduction

Laser Vision Correction Surgery alters the curvature of the cornea, the clear shield of the front of the eye, changing the power of the eye similar to the way a contact lens changes the power of the surface of the eye.  A contact lens creates an artificially flatter, steeper or more aspheric (oblong) front surface of the eye based on the patient’s prescriptive needs.  LASIK changes the power by altering the tissue just beneath the surface of the cornea.  First, a flap from the top of the corneal tissue is created by running a blade or a laser called a Femtosecond laser tangentially across the cornea.  The flap is left hinged, pulled to one side and laid down.  The flap looks similar to a thin contact lens.   The front surface of the flap is the surface of the cornea and the flap is the top 5 to 11% of the central 6-9 millimeters of diameter of the cornea.  During LASIK where the flap is “cut” with a blad, the blade is located within a lathe-like device called a microkeratome.  The microkeratome is placed on the eye and a suction mechanism keeps the eye still and the microkeratome from moving out of alignment.  The microkeratome lathes the cornea to create the flap tangentially to the surface.  The flap is left hinged thus is not totally separated from the underlying cornea. This is done so it is not displaced, lost or mangled, because after the laser is applied, the flap will be replaced. The laser is programmed with the amount of power necessary to correct your vision prior to the surgery.  During surgery the corneal surface is flattened by the laser beam which is cool ultraviolet energy. The exposed surface of the cornea just beneath the flap (corneal stroma) is the tissue altered with the ultraviolet energy of the laser.  After the stroma is altered by the laser, the flap is laid down like a contact lens and capillary forces (suction) between the underside of the flap and the newly lased surface of the corneal interior keep the flap in place while healing begins.  The higher the vision prescription was pre-operatively, the longer time it takes for the final post-operative healing to stabilize.

A BRIEF HISTORY OF REFRACTIVE SURGERY

The first refractive surgeries probably were performed in ancient Greece.  These crude surgeries involved removal of cataract (clouding of the lens in the eye).  In the 1850’s, the first refractive lensectomy (removal of the lens of the eye for purposes of correcting high myopia) were performed. In the late 19th century, the first corneal surgery for correction of astigmatism was performed.  Astigmatism was reduced with a horizontal incision in the corneal stroma.  In the early 1940’s the first keratectomy was performed in Japan.

In the late 1940’s and early 1950’s, a pioneering surgeon in South America, Prof. Jose Barraquer, invented a procedure called Freeze Keratomilleusis . The word Keratomilleusis is derived from the greek keras (horn-like – cornea) and smileusis (carving).   Dr. Barraquer would create a flap of the anterior surface of the cornea.  He would reshape the curvature of the exposed interior surface by removing a small segment of corneal interior and cryo-lathing (freezing and lathing) the excised corneal tissue to the desired power.  He would then replace the reformed excised corneal tissue and lay down the flap.  Barraquer conceived of Keratomilleusis In Situ, or within the cornea and this procedure was later named “Stromectomy” by Krawawicz and Pureskin.  Pioneers in this surgery include three Houston Ophthalmologists who performed Myopic Keratomileusis (MKM) on patients who were not candidates for RK surgery (Radial Keratotomy- see below). Keratophakia came next.  In Keratophakia, a graft of donor cornea was added to the corneal stromal bed to increase the power of the cornea. Barraquer then pioneered Barraquer-Krumeich-Swinger Non-Freeze Keratomileusis Technique, which involved separating a cap of tissue from the surface of the cornea and using a suction dye to make the desired refractive change instead of freezing tissue, which damaged the corneas to an extent.  This technique could not correct for astigmatism and in some cases, caused irregular astigmatism.

The 1960’s saw the advent of Radial keratotomy (RK), pioneered in Russia by Fyodorov.  RK involves making a series of spoke-like incisions in a radial fashion towards the periphery of the cornea.  The incisions scar and flatten the total curvature of the cornea.
Epikeratophakia (Kaufman and Werblin) came next.  In epikeratophakia, the surgeon was provided with a processed donor corneal graft for insertion into the patient’s cornea.  There were many drawbacks to this procedure including re-epithelization (skin forming) of the donor corneas, epithelial ingrowth, necrosis (death) of the donor graft and severe visual disturbance including haze.

The microkeratome was the first type of device developed to lift the surface of the cornea and form a cap in all of the aforementioned procedures.  A surgeon named Luis Ruiz improved the removal of the cap of tissue with his development of a new kind of microkeratome, providing a more perfect cap.  The device consisted of a track that the blade advanced along which controlled the depth of the ablation, smoothness of the ablation and reduced surgical difficulty to some degree.  This was the first advanced microkeratome.  Surgery using the new microkeratome came to be known as ALK (Automated Lamellar Keratoplasty)   Trokel first described the use of an excimer laser to remove corneal tissue in 1983.  Seiler improved on this process when he performed the first excimer treatment on a human eye in 1987.  Marguerite McDonald was the first person to apply the laser to a seeing human eye with PRK.   Lucio Buratto of Italy used the excimer laser to replace the cryo-lathe in 1989.  His positive results led to approval of use of laser for laser keratomilleusis, or reshaping of the cornea.  In June of 1991, Dr. Stephen Brint performed the first LASIK procedure (Laser Assisted In-Situ Keratomilleusis) on a corneal section.  Pallikaris came up with the idea of creating a flap and working on the eye without removing any of it to be reshaped.  In Dr. Barraquer’s epikeratophakia, a section of cornea was removed and cryolathed.  In excimer ALK, a section was removed and the laser was used instead of the cryolathe.  Pallikaris set the stage for the "In Situ” procedure, or “in the eye” lathing process.  The flap is lifted and a computer controlled laser is used to gently reshape the surface underneath the flap with extreme precision.  The laser used is an Excimer laser (Excimer stands for Excited-Dimer) The excimer uses Ultra Violet energy to break the molecular bonds (dimer’s) of the exposed area under the flap.  The energy evaporates the exposed layers of cornea beneath the flap molecule by molecule within a 6 to 9 millimeter diameter zone usually.  In Myopic (nearsighted) patients, the zone is created deepest in the center and shallower toward the periphery of the zone, creating a greater concavity (flattening or decrease of curvature) of the cornea’s curvature.  The higher your myopic prescription, the deeper the zone needs to be, thus the greater the concavity.  A –4.00 powered eye will have a shallower, less concave laser ablation with the excimer than a person with –6.00 power.  The cornea is only so thick, so some people with extremely high prescriptions are not good candidates for laser vision correction; the laser would have to go too deep, creating too much concavity in the central part of the cornea to achieve the desired effect.   Farsighted (Hyperopic) eyes must be lasered circumferentially toward the periphery of the flap area, creating more convexity to the area in front of the visual axis by steepening the periphery.  Astigmatism is corrected with concavity lasered linearly along a particular axis of prescription.

Correction for Myopia	Correction for Hyperopia	Correction for Astigmatism
(nearsightedness)	(farsightedness)	(axial refractive error)
concave curvature produced	convex curvature produced	Axial concave curve produced

Each laser pulse removes corneal tissue 1/100th the thickness of a human hair, so a precise amount of tissue removal can be controlled for.  The laser provides technological improvement to the manual procedure performed by Dr. Barraquer.  The laser procedure is not a completely new surgical entity, but an improvement to an established procedure.

Radial Keratotomy (RK) came of age in the late 1970’s and was pioneered in Russia in the 1960’s.  RK is a surgery where the cornea is scarred by making radial incisions that in most cases penetrate 90% the depth of the cornea. 

The incisions scar the cornea, the scars pull the corneal tissue flatter, thus changing the its power, enabling patients who are nearsighted or have astigmatism to see better.  RK patients have experienced many problems years after surgery.  The major difference from laser eye surgery is that RK compromises the structural integrity of the eyeball because of the deep, spoke-like incisions radially around the cornea that scar.  Scarred human corneal tissue is never as strong as healthy tissue.  Patients who have been in accidents or have had blunt trauma to their eyes after receiving RK surgery have, in some cases, lost the involved eye due to the scar opening up.  Scar wounds of patients who have undergone RK have become infected.  Patients who have had to use contacts after RK are at greater risk for infections, so contact lens wear may may not be an option after RK if the surgery doesn’t achieve the desired results.  Limits in post-operative options are undesirable.  Some patients suffer from severe glare at nighttime. 

Since the success of the laser, new players have entered the surgical vision correction market.  Intra-ocular contact lenses are gaining in popularity.  A lens is inserted within the eye that corrects the refractive error.  The lens can be placed in the Anterior Chamber (the area between the underside of the cornea and the front of the pupil).  The most popular type of Anterior Chamber IOL is the Phakic IOL.  The lens is positioned in the tiny space between the front of your natural lens and the back of your iris, known as the Ciliary Sulcus.  Because this space is so narrow, there is significant concern for problems from these lenses, especially increased pressure within the eye (glaucoma). The second type of IOL is a posterior chamber IOL. This lens is placed in within the space that the natural human lens is removed from, known as the Capsule.

AM I A CANDIDATE FOR REFRACTIVE SURGERY?

The most important factor in determining candidacy for refractive surgical procedures is your acceptance of risks and knowledge of realistic expectations for outcomes concerning your procedure.

The second most important factor determining your candidacy for a refractive surgical procedure is the stability of your prescription.  Why second?  Almost everyone has one refractive surgical option or another.  If you can accept the risks and know what to expect, you most likely can find a refractive surgical procedure that will meet your prescriptive needs.  Whether your vision changes regularly or not, your vision is likely to change in the years following the procedure.  If your vision changes regularly, you are more likely to notice a change in your vision after a vision correction procedure than someone who’s vision does not change regularly.  Refractive procedures correct most of your refractive error very effectively; they do not fix nearsightedness, farsightedness or astigmatism forever.  While enhancement is an option for most laser surgery patients who change down the road, the amount of times an enhancement procedure can be attempted is limited.  Every time a procedure is enhanced, the cornea gets thinner and if too thin, enhancement could lead to problems discussed later in the site.  Another important factor is determining which refractive procedure is best for you.  The prescriptions and physical characteristics of your eye determine the best procedure, and you need the advice of a doctor to decide which procedure is right for you.  Refractive surgical correction procedures include Laser procedures (PRK, LASIK), Intrastromal Corneal Ring Segments (Intacs Corneal Rings),  clear lens extraction,  intra-ocular lens implantation, Radial Keratotomy, Astigmatic Keratotomy and in the future, Gel Injection Adjusted Keratoplasty. 

Contraindications for LASIK surgery include Keratoconus, a corneal condition that involves thining of the cornea, rheumatoid conditions including some of autoimmune conditions, recurrent uveitis, glaucoma or patients who have irregular corneas or corneal epithelium.

WHAT COULD HAPPEN TO YOUR EYES DOWN THE ROAD AFTER LASER

LASIK surgery gently reshapes as much as the top 12% of the cornea and does not cause significant scarring of the cornea.  Laser effects are limited to the most anterior part of the anterior of the eye.  Thus, the integrity of the eyeball is essentially the same after LASIK surgery as before.  RK surgery scars the cornea to a depth of 90% in most cases and the structural integrity of the eyeball is ruined leaving farsightedness, astigmatism, glare, hypotony (low eye pressure) and eye loss secondary to infection or trauma down the road.  Many adults suffered Cornea abrasions as children from a tree branch, a paper edge or other type of injury.  In many of these instances, the scratch was twice as deep as the depth to which LASIK surgery goes to correct your vision.  Not only was the scratch deeper than LASIK surgery, but the edges of the insulting object may have been jagged, dissimilar to the smoothness of the LASIK ablation.  Most adults who had deep scratches as children have no recurring problems even into old age.  The ones who do have problems may suffer from a condition called Recurrent Corneal Erosion Syndrome (RCE), which causes a sharp eye pain once in a while upon awakening, from reinjuring the old scar.  The LASIK flap is precisely sculpted with a stainless steel or titanium blade or a Femtosecond laser and the ablating laser is extremely precise, each pulse removing tissue 1/100th the thickness of a human hair, creating a very smooth, non-scarring ablation. The smooth laser ablation creates a surface that does not tend to erode, as opposed to the rough abrasion that causes erosion in RCE.  An overwhelming amount of RCE is caused by abrasions from organic matter such as a tree branch.  While RCE is a possibility down the road for patients who’ve had LASIK, it is not a probability.  One interesting fact is that the treatment for RCE is more laser surgery on the surface of the eye!  Surgeons treat RCE with a version of Photorefractive Keratectomy (PRK), called Photo-Therapeutic Keratectomy (PTK) which removes the old, eroding scar tissue and smooths the surface.  This treatment is very effective.  

Regression of vision is a risk.  Regression is common in LASIK, but it is uncommon to regress to the pre-operative refractive error.   Several cases have been reported in the literature of full regression of benefit from LASIK surgery.  If  LASIK surgery fails to correct a patient to their desired vision, patients still have 3 options to correct their vision.  Patients may wear eyeglasses to get the extra vision they need.   Patients can still wear contact lenses (RK patients in most cases cannot) or they may have LASIK enhancement surgery to get closer to their desired visual outcome if medically feasable.    

Retinal Detachment is a risk of LASIK surgery.  Studies have shown that if a retinal detachment is to occur, on average it occurs 11 months post-operatively.  This is the reason the pre-operative dilated eye examination is so important, followed by dilated eye examinations annually post LASIK surgery.  This can help to identify those at risk for Retinal Detachment and those patients can be followed closely by a Retinal Specialist.  They can also be made aware of signs and symptoms that may indicate Retinal Detachment, allowing early detection.  Retinal detachment can be treated successfully if caught within 24 hours, so it is important for doctors to inform patients of the signs and symptoms to look out for.  If not recognized and treated, Retinal Detachment could lead to permanent loss of peripheral vision and even blindness in the affected eye.

Exposure to laser rays has no risk associated with it. The Excimer laser uses ultra violet energy.  Excimer energy is absorbed by molecule’s that make up the cornea.  Excimer energy evaporates tissue and the energy dissipates within the front half of the Cornea.  To demonstrate how easily Ultra Violet energy is dissipated, surgeons performing the procedure have to wipe away all moisture from the surface being treated, because if there is moisture, the energy will be spent breaking the bonds between the water molecules instead of lasing the cornea beneath!  There are few if any, side effects from Excimer Ultra Violet radiation.  There is no potential for health problems from exposure to the laser energy down the road, because the ultra violet energy of the excimer laser dissipates very rapidly; within milli-seconds (thousandths of a second) and is limited to the superficial layers of the cornea.  Eye health problems caused by Ultra-Violet radiation, including cataracts and macular degeneration, are caused by long-wavelength UV radiation including UV-B and UV-C radiation.  The excimer wavelength is a much shorter wavelength of energy and as such, is unable to penetrate the anterior layers of the cornea.  It’s energy is dissipated on breaking the molecular bonds during the laser process, so very little if any penetrates to the level necessary to cause cataract and no excimer energy penetrates to depth of the retina, where macular degeneration would be of concern.

The older of the two Laser vision correction surgeries, PRK, is a totally superficial procedure.  PRK is performed on the surface of the eye after the thin layer of epithelium (transparent skin) just beneath the layer of tears is removed.  Once the epithelium is removed, the laser changes the curvature of the anterior of the cornea as in LASIK.  The epithelium re-heals over the anterior surface.  In PRK, there is a greater risk for corneal haze (discussed later) and there is moderate to severe discomfort for 1-3 days after surgery.  In PRK, a thin, transparent layer of the cornea, Bowman’s Layer, is destroyed by the Laser.   The function of Bowman’s layer is unknown; it is a densely packed layer of collagen and some research suggests that it is the basement membrane of the epithelium of the cornea.  LASIK does not damage Bowman’s layer.  Other research has shown that the epithelium reheals stronger after Bowman’s layer is destroyed.  No one is sure of the consequences of destruction of Bowman’s layer, but Recurrent Corneal Erosions (RCE discussed before) are unlikely as PRK is used to treat corneal erosions from other sources.  Possible complications include but are not limited to dryness and glare years after PRK and Corneal Ectasia (thinning and steepening of the central cornea) although these have not been reported as significant problems as of yet.

COMPREHENSIVE  RISK ANALYSIS OF LASER CORRECTION

Certain risks occur secondary to surgical procedure; others may occur during surgery but are not a direct result of surgical procedure. Risks include any and every adverse event that could feasably occur that may not have happened had the person remained outside the laser suite.  Remember, this list is designed to be extremely comprehensive, so while certain items in the list occur, others may have never occurred but are a possibility. Operative risk involves risks the patient assumes during and immediately after the surgery.  Post-Operative Risks involve changes during and after the healing process.

OPERATIVE RISK

The first step in LASIK surgery is creation of the LASIK flap.  A simple eyedrop, Proparacaine or Tetracaine, is used to anaesthetize the cornea.  The patient is laid on the operating table and their lids are held apart painlessly by a metal device called a lid spreader. The cornea is marked so that the flap can be laid down in with proper positioning after the laser has been applied.  A circular metal ring is placed on the eye.  The ring is part of a suction unit that holds the lathe-like microkeratome in place on the eye.  The circular part of the microkeratome makes contact around the area where the clear cornea meets the white of the eye, the Corneal Limbus.  When the device is positioned properly on the “limbal area”, suction is applied by the surgeon using a foot pedal, causing the pressure in the eye to approach 80 mmHg with a minimum pressure of 65 mmHg (normal eye pressure 10 to 21 mmHg).  The high pressure causes a tempory interuption of blood flow to the retinal photoreceptors causing the vision of the patient to dim or go black for a brief period of time.  At this stage, the patient may experience a feeling of pressure but no pain.  During the time that the vision is dimmed, the motorized lathe of the microkeratome runs tangentially to the corneal surface, lathing the top 10% of the total corneal thickness, creating the LASIK flap.  The flap is left attached by a hinge, and the hinge is usually left attached on the temporal side of the cornea, so that the flap is not physically separated from the eye.  (Some surgeons prefer to lay the flap inferiorly, hinged on the bottom toward the lower lid of the eye, and some surgeons even fold the flap on itself to keep debris from attaching to it.  The flap is created tangentially across the surface of the cornea, not perpendicularly through the cornea as in RK incisions.

RISK 1 – It is possible that the microkeratome may malfunction, cutting through and separating the cap from the cornea beneath, without formation of the “hinge”.

DISCUSSION:  While possible, it is extremely rare for cap separation to occur, it could be the result of a faulty microkeratome.  Microkeratomes are designed with “stops” so the incising can only go so far.  This risk has greatly decreased over time, as Microkeratomes have improved in design and function.  Most surgeons utilize trained ophthalmic assistants to test and retest the microkeratome seconds before use.  Flap problems may also occur if a foreign body is on the tracks that the microkeratome follows and causes a malfunction in the device. The microkeratome is treated with pressurized air to blow away foreign debris that lie within the workings of the microkeratome that may cause it to malfunction. While one microkeratome is in use in most laser centers, the other one is being cleaned and treated. If the flap is cut too shallow and is extremely thin, it may separate in the process of lifting the keratome away from the suction ring.  This is caused by a lack of suction or loss of suction from the suction ring.  A buttonhole flap occurs more commonly in Hyperopic (farsighted) prescriptions.  Buttonhole flaps are flaps that are cut thin and cause flap displacement of a “buttonhole” section; only the steepest part of the cornea.  If your corneal curvature is greater than 48 Diopters, this is of greater concern. Surgeons can prevent this from occurring in most cases through careful assembly and cleaning of the microkeratome device and confirming appropriate levels of suction before creating the corneal flap.  Adequate suction is when the pressure in the eye is brought to greater than 70 mmHg.  There are certain signs the surgeon uses to determine adequate suction.  The pupil will dilate, the patient will report dimming of vision, a tonometer (pressure testing device) will have the appropriate reading and the suction unit will read appropriately on its dial.  Flap separation can occure in cornea’s shaped like a football: one meridian, for instance the “X” axis of the cornea is much flatter than the “Y” axis. The microkeratome incision will be extremely thin nasally and temporally in this case and the flap may separate.  If Cornea curvatures are less that 41, a microkeratome called a “hansatome” should be used to create the flap instead of other microkeratomes to avoid flap complications.

WHAT HAPPENS IF: If a flap is separated from the eye, it is replaced immediately.  Capillary action holds the flap in place and the cornea re-heals well enough to see within hours and is completely rehealed 3 months later.  The patient will not be able to receive LASIK surgery for 3 to 6 months depending on surgeon recommendations but may then return for the procedure. The excimer laser correction could further alter the irregular stromal corneal bed.  The flap should be replaced and left for at least 5 minutes.  The patient should be monitored every week.  The repeat procedure in 3 to 6 months will need to utilize a deeper incision and patients can still achieve an excellent outcome if this occurs. Flap displacement occurs in 1/1000 cases

RISK 2 – It is possible that the flap, while separated from the eye, may be lost or mangled.

DISCUSSION:  If the flap is no longer attached to the Cornea the small possibility exists that it may be misplaced or mangled and cannot be replaced.  A malfunction could occur and the microkeratome could mangle the flap.  Also, if the flap is separated, since it is thin and transparent, it is difficult to locate and could get lost as a result.  If the cap is separated, it may have been caught in the microkeratome device.  The microkeratome goes right from the surgeon’s hand to be soaked in an alcohol or bleach solution and is then sent to an oven called an autoclave for sterilization. If the cap is separated, it is vital that the surgeon identify the cap before proceeding with any instrumetation sterilization.  A cap that is soaked in alcohol or bleach or autoclaved is ruined permanently in most cases.

WHAT HAPPENS IF:  If a flap is lost, and at the time of this writing this has never happened, then the patient will undergo PRK surgery then and there if prescriptively they are PRK candidates.  PRK has, in many cases just as good an outcome as LASIK surgery, however healing takes longer, there is considerable discomfort in the healing process and it may take a week until the vision clears up.  PRK surgery is essentially LASIK surgery on the surface of the eye, so no flap is needed.  Visual outcome with PRK depends on the amount of prescription the patient requires, as higher prescriptions may run into more risks of undercorrection in instances of flap loss.  Haze (see below) is also a more common risk of PRK.  PRK is contra-indicated for prescriptions exceeding 6 Diopters (-6.00) when using a 6 mm Laser zone.

RISK 3 – It is possible that the patient may get an eye infection.

DISCUSSION:  If a patient gets an infection it can be nasty.  At the time of this writing there have been 21 infections reported in the literature after over 1.2 million surgeries worldwide.  Of course, many other infections have occurred that were not published in the medical literature. The incidence may be approximately 1/5000.  Infections are first recognized in the first week to first month after the procedure.  This is why it is so important to have good pre and post-operative care.

WHAT HAPPENS IF: If there is a serious infection, the patient must take antibiotic eyedrops and may be uncomfortable and blurry for several days, even weeks.  Mild infections may clear up fast, but flap infections are quite serious and in some cases patients have required more surgery, even needing corneal transplant surgery to restore vision.  Patients who have an infection should stop non-steroidal medications and be placed on flouroquinolone antibiotic eyedrops.  If these are ineffective, fortified topical flouroquinolone antibiotics may be required. Rare cases may require oral or IV antibiotics. Infections can affect the final visual outcome; they can be painful and leave the patient with blurry vision for weeks.  Infections can happen in any surgery where the interior of the body is exposed to air, even eye surgery.  Patients receive prophylactic antibiotic eyedrops before, during and after their LASIK surgery to minimize the risks.  Serious infections are extremely rare and have resulted in a need for corneal transplantation surgery.

RISK 4:  It is possible, while highly unlikely, for the cornea to be perforated during the creation of the flap.

DISCUSSION:  This particular risk has never happened, but should it, it would be the worst outcome possible for refractive surgery.  If it occurred, it would be because the depth plate for the microkeratome, which determines the depth to which the flap is cut, was not installed at all, installed improperly or incompletely.  The outcome of this most likely would be blindness in the affected eye.  Formation of an imperfect flap occurs 1 out of every 500 to 1000 procedures

RISK 5 – It is possible that blindness may result from LASIK surgery

DISCUSSION:  Blindness is a real and potential risk of any eye surgery.  No one has ever gone blind from LASIK surgery. There are innumerable unforseen circumstances, such as natural disasters, mechanical failures, etc.  Any unforseen circumstances may lead to surgical failure, however when operating on an eye, blindness is a risk just as death is a risk of heart surgery and hearing loss is a risk of inner ear surgery.

RISK 6:  The excimer laser requires Flourine gas to function.  If the gas dispensing mechanism is damaged or the tank punctured and Flourine leaks into the room and the room is not adequately ventilated, respiratory and other health conditions could result.

Discussion:  A “worst case” fluorine leak is considered to be one where all the premix gas in a full bottle within the laser is allowed to escape into the room with no regulator control restriction.  There is a control within the laser that absorbs flourine should a leak be detected.  This device called an internal halogen scrubber removes any flourine from inside the laser. There is a risk that this device could fail.  Should a leak occur within a poorly ventilated room, the highest level of flourine concentration in the laser suite would be reached in about 4 minutes and would slowly drop to undetectable levels within 1 hour.  A “worst case” leak is defined as a maximum concentration of 6 PPM dropping to .1 PPM.  The IDLH is defined as that concentration which, without respiratory protection, a person could escape within 30 minutes, without any impairing symptoms or any irreversible health effects.  The IDLH level is 25 PPM; even in a worst case leak, it would take much less than 30 minutes to escape from the room, and the room would require a concentration 4X greater than possible with available flourine in the Excimer to cause physical irritation or health concerns.  THIS HAS NEVER HAPPENED

RISK 7:  It is possible to have a branch retinal artery or branch retinal vein occlusion secondary to the microkeratome procedure.

DISCUSSION:  The retina, or sensitive nerve tissue in back of the eye, is supplied by a network of small, fine arteries and veins of  the Retinal Vascular Arcade.  These vessels are very small in diameter. During the microkeratome procedure, the increased pressure placed on the eye by the microkeratome suction can close off a vein or artery and, if the pressure remains for too long, cause the vein or artery to leak into the retina.  This can lead to loss of vision in one or more quadrants of the visual field.  In some cases the vision may return, in others there may be a permanent loss of visual sensitivity in the part of the visual field that corresponds to the broken vessel. This loss is called a “Scotoma”

WHAT HAPPENS IF: Follow up by a retinal specialist is necessary to determine the extent of damage and monitor progression or regression of symptoms.  This is very rare but has happened in the past. Refrain from taking aspirin or non-steroidal anti-inflammatory medications OK’d by a retinal specialist.

RISK 8: It is possible that an epithelial defect may be caused during surgery that leads to pain, prolonged visual recovery, epithelial ingrowth, infection or interface inflammation.

DISCUSSION:  Epithelial defects are defects in the thin layer of skin-like cells that are on the surface of the cornea.  The microkeratome device cuts through this layer during the flap procedure.  If prior to surgery a patient has a history of Recurrent Erosion Syndrome, a weekend epithelium from anaesthetic eyedrops, a traumatized cornea from excessive manipulation during surgery or are over 60 years old, they run a greater risk of these complications.  Problems related to flap epithelial defects include pain, longer visual recovery time, epithelial ingrowth (referenced above), infections, Sands of the Sahara (discussed above) and in extreme cases where proper follow up care is not received, flap melt, corneal haze and scarring.  LASIK should be avoided in patients with epithelial defects or Anterior Basement Membrane Dystrophy.

WHAT HAPPENS IF: Patients who experience this problem are placed on antibiotic eye drops every hour and lubricating eye drops or ointment until the defect heals.  Sleep or rest with eyes closed is recommended.  Some larger defects may require use of a bandage contact lens placed over the cornea to assist in healing and to keep from blinking over the defect.  These patients need to be followed weekly for 1 month to monitor for signs of epithelial ingrowth.

RISK 9:  It is possible that the pressure from the microkeratome causes a narrow-angle or closed-angle glaucoma.

DISCUSSION:  Glaucoma is defined as damage to the retinal photoreceptors (sensitive nerve tissue in back of the eye) secondary to increased intra-ocular pressure (pressure inside the eye), decreased vascular supply to the optic nerve (nerve from the eye to the brain) or idiopathic apoptosis (cell death) of the retinal photoreceptors.  Glaucoma after LASIK surgery can occur when the pressure placed on the eye by the microkeratome compresses the fluid drainage system of the eye (Trabecular Meshwork) or causes the Iris (colored part of the eye) to press up against the drainage system and block outflow of fluid from the eye.  Think of the eye as a sink, where there is a faucet (Ciliary Body behind the iris) that creates fresh fluid to circulate in the eye, and a drain behind the cornea (Trabecular Meshwork) where the circulated fluid leaves.  This is a dynamic system and ideally should be in equilibrium (as much fluid as is produced within the eye should drain out of the eye, maintaining regular pressure; not too high, not too low).  The same amount of fluid that is produced should leave the eye through the Meshwork.  If the drain is clogged by the Iris or narrowed, and more fluid is produced than is leaving, the eye pressure can increase and the force of the increased pressure is directed backward.  The increased pressure on the sensitive nerve fibers (retinal photoreceptors) interrupts flow of nutrients along the nerve fiber cell (axoplasmic flow) and the fiber dies.  For some unknown reason, the fibers in the peripheral retina die off first causing vision to be lost from the outside-in.  Pressure from the microkeratome has the potential to narrow or close this angle, although this is extremely rare.  One recent study found prolonged microkeratome suction time can damage the nerve tissue layer of the retina.  This study found that, on average, if there is less than 20 seconds of pressure applied by the microkeratome, there will be no nerve fiber layer damage. Experienced surgeons are faster with the  microkeratome so patients run less of a risk of nerve fiber layer damage with experienced surgeons.  Patients exposed to microkeratome pressure for 20 to 40 seconds showed variable nerve fiber layer damage.  Patients exposed for greater than 40 seconds showed a 7-10% loss of nerve fiber layer.  When Alphagan ophthalmic eyedrops (pressure-lowering eyedrops) were applied to eyes pre-operatively, the incidence of nerve fiber layer loss secondary to prolonged microkeratome procedures decreased dramatically.  Other studies have found no loss of nerve fiber layer loss regardless of microkeratome time.  All patients with family history of glaucoma should be treated with LASIK instead of PRK

WHAT HAPPENS IF: If an angle is narrowed as a result of the microkeratome procedure, drops may be used to open the angle.  It is possible that a different laser may be used to increase the outflow also.  This occurrence is extremely rare and may require follow up by a glaucoma specialist.  It may be treated successfully in many cases or may result in progressive vision loss in the affected eye.

RISK 10: It is possible that the surgeon may accidentally re-position the flap incorrectly and it is even possible that the flap may be positioned upside down if the flap is separated from the eye and an attempt is made to replace it.

DISCUSSION:  If the flap is mal-positioned, a poor visual result may be the outcome. 
If the flap is re-positioned upside down, corneal haze, improper healing, irregular astigmatism, interface keratitis, epithelial ingrowth and striae (folds in the cornea; these are discussed later in our essay) are serious risks.  If a flap is removed accidentally, it can be fit back onto the surface beneath it rather easily, like a puzzle piece.  If the stromal bed is lasered and the flap is replaced, it may not fit well and could result in a poor visual outcome for one or more of several reasons.

WHAT HAPPENS IF: A poorly positioned flap can be lifted and replaced, however, if the surgeons markings of the original flap position have washed away in the tears, normal placement may be difficult to achieve.  The surgeon will want to insure that there are no striae (folds in the cap) in order to achieve the best result throughout the healing process.  In the rare event of an upside down flap, more surgery may be necessary and it is possible that the cap may be damaged beyond repair, causing loss of best-corrected visual acuity, glare, haze, LIK (discussed later) and poor refractive outcome.

RISK 11:  It is possible that the microkeratome blade is imperfect from the manufacturer and, as a result, a horizontal linear defect may occur within the flap.

DISCUSSION:  This is an extremely rare occurrence, especially with a careful operative staff and surgeon.  If the defect occurs across the visual axis (the line of sight) the results may be visually devastating.

RISK 12: Formation of corneal irregularities called “Central Islands” may occur in surgery performed with a broad beam laser as opposed to a scanning laser.

DISCUSSION:  Central Islands occur secondary to accumulation of small fluid “lakes” in the center of the laser incision.  When the laser lases a “lake” (water) instead of the cornea beneath the lake, the area under the lake remains raised relative to the cornea that was lasered around it.  These lakes occur since the concavity of the lasered area is greatest toward the center of the cornea in myopia treatment, directly in the line of sight.  Surgeons have to be careful not to overcorrect the central cornea as a divot may result, the opposite of an island (kind of an indentation) that is very difficult to correct.  Central island occur in 1/200 cases performed with a broad beam laser.  Technological advances in laser refractive surgery will eliminate central islands by eliminating the central accumulation of fluid.

WHAT HAPPENS IF:  Central islands caue a loss of uncorrected visual acuity, loss of best corrected visual acuity, irregular astigmatism, double images and undercorrection.  Central Islands should be monitored by your physician or surgeon with corneal topography.  The height and size of the islands are determined by the Munnerlyn formula.

Height of Island in Microns = diameter of Island2 X diopter height
                                                                    3

The appropriate laser treatment is calculated from this and applied to the islands.

RISK 13:  LASIK recipients run a risk of having the laser ablation de-centered off the visual axis.

DISCUSSION:  Decentered ablations or misalignment of the laser can result in distortion or double images, especially at night.  There may be a loss of best-corrected acuity as well.  One of the reasons for decentered ablations is a dilated pupil, so it is imperative that pre-operative evaluation with dilation of the eyes be performed 4-7 days before the operation, preferably more than 1 week before.  Two new technologies, pupil-tracking lasers and topography-assisted lasers which track the contour of the cornea exactly will reduce the amount of decentered ablations dramatically.  Broad Beam lasers frequently are the cause of decentered ablations.

WHAT HAPPENS IF:  Treatment of the optical zone with a more advanced laser, such as a topography-assisted or pupil tracking laser.

RISK 14:  It is possible for the wrong axis of astigmatism to be lasered onto your eye.  It is also possible for the wrong prescription to be lasered onto your eye.

DISCUSSION:    At busy clinics, it is important that staff and surgeon insure patient records do not get mixed up.  It is possible that a mix up may result in someone elses prescription being lasered on your eye.  It is also important that the patient’s prescription be double and triple checked and the patient record be coordinated with the patient’s name tag, to insure the proper patient is being lasered. 

Myopia (nearsightedness) and Hyperopia (farsightedness) are indicated by (-) sign and (+) sign respectively before the prescription numbers.  A –4.00 power indicates 4 Diopters of myopia.  When someone has astigmatism and myopia or hyperopia, prescriptions are described by 3 numbers. Those numbers represent the myopia, the astigmatism and the axis.  The axis is the angle at which the astigmatic power is aligned, from 0 to 180 degrees.  Astigmatism at 180 degrees is defined as axis 180, or (X 180).  If the example above had not only –4.00 diopters of myopia, but –2.00 diopters of astigmatism also, the prescription would be written as  –4.00 = -2.00 X 180 (-4.00 diopters myopia with –2.00 diopters of astigmatism position with its axis at 180 degrees).  To make it even more confusing, the formula for this patient can be written in two forms, minus cylinder and plus cylinder.  The example is written in minus cylinder and a mathematical transposition can convert the minus cylinder format to plus cylinder format.  How it is transposed is beyond the subject matter in this essay, however, in plus cylinder, the prescription would be written as –6.00 = +2.00 X 090.  You can see that, when transposed, the exact same prescription can have two very different appearing number sequences.  If a referral doctor measures you in the plus cylinder format and the axis is transposed incorrectly at the laser center, the wrong axis could be lasered onto the eye.  If the referral doctor measures you in the plus cylinder format and transposes it incorrectly herself/himself and it is not verified prior to surgery, it could result in the wrong axis being lasered onto your eye.  If the flap markings are not aligned as the flap is laid down, astigmatism can be induced, also.  Cylinder axis should be checked more than 3 times before surgery.

RISK 15: It is is possible that the laser may malfunction during surgery.

DISCUSSION:  If the laser malfunctions during surgery, the flap will be replaced and you will need to return for enhancement surgery 1 to 3 months postoperatively.

WHAT HAPPENS IF: There is the possibility for undercorrection if the laser has stopped working halfway through the procedure.  Enhancements are usually successful.

RISK 16: Misalignment of the corneal flap after flap replacement may cause Flap Striae to form.  This may also occur secondary to movement of the flap during the first postoperative day through rubbing or squeezing the eye

DISCUSSION:  Flap striae appear within hours of surgery.  The longer the striae are present, the more difficult it is to remove them.  They become imbedded in the flap over time.  Flap striae must be treated if they extend through the visual axis, decrease vision or induce irregular astigmatism.

WHAT HAPPENS IF: Patients in general should keep eyes closed as much as possible on the first pre-operative day.  This helps promote healing.  Striae occur in 1/300 cases and may become fibrosed and dense, causing decrease in best corrected acuity and irregular astigmatism, but this is rare.  It is more common in surgeries with thin, irregular flaps.

POST-OPERATIVE RISKS

RISK 17 – It is possible that the desired results of surgery will not be attained and the patient may be left with residual amounts of nearsightedness, farsightedness and/or astigmatism

DISCUSSION:   LASIK surgery is quite precise.  Measurements for programming the laser for your surgery are taken several times by your personal doctor and several more at the laser clinic.  The power that is lased into your cornea to correct your vision will bring your cornea close to the desired visual result.  This is evidenced by the fact that most people receiving LASIK surgery achieve vision better than 20/40 the first day after surgery.  How your eye will heal is the one variable that cannot be controlled for, so even if you have a perfect surgery, if you are an “over aggressive” healer, your healing may overshoot the desired result, leaving you with the opposite refractive error then what you came in with.  If you are an “under aggressive healer” you may end up with a lesser form of the same refractive error you came to be treated for.  The surgeon’s nomogram is the calculation the surgeon uses to determine how to approach a surgery. The nomogram is developed based on several factors including keratome skill, previous surgical results, humidity and other factors. It takes into account variables that may affect the surgical outcome and determines what steps the surgeon takes to insure the best outcome.  Each surgeon develop’s a nomogram that works best for them.  The nomogram is developed throughout the LASIK learning curve.  The learning curve for LASIK varies, but has been estimated to be 1000 eyes, or 500 bilateral LASIK surgeries. How you heal is based on how effective the surgeons nomogram is and how you, as an individual, heal.  You may achieve the desired result or you may not.  It is important to have reasonable expectations regarding Laser Vision Correction.  98.7% of LASIK surgeries end up better than 20/40 after the first surgery.  20/40 is good, functional vision.  You can drive with 20/40 vision, play sports, go to the movies, view your alarm clock in the morning and shower without glasses or contacts.  You may need a very slight prescription to achieve precision vision after LASIK surgery.   It is better to think of 20/20 vision after laser vision correction as a very pleasant side affect that happens most of the time.  Of the 98.7% of LASIK recipients who achieve 20/40 or better vision after the first surgery, 85% or more end up 20/20.  Patients under the age of 26 years tend to regress to undercorrections while patients above 43 tend to regress less and end up overcorrected more often.

WHAT HAPPENS IF: 3 months down the road, if you are unhappy with the visual outcome, you can have an enhancement procedure to bring you closer to the desired result, if medically feasable.  Pachymetry is a measurement that allows the surgeon to determine corneal thickness.  If the cornea is not thick enough, enhancement surgery may not be advised.  During the second procedure, you undertake the same risks as the first procedure if the microkeratome needs to be used to lift the flap.  Less risk is involved if the flap is able to be lifted, and that can happen in a narrow window less than 6 months after the primary procedure.  Second procedures are more common for patients with higher prescriptions patients with higher prescriptions should think of LASIK as a two-step procedure; an initial correction and an enhancement.  You also have the option of wearing a lesser eyeglass prescription or contact lenses to give your vision an extra boost postoperatively.

RISK 18: It is possible that you may be corrected as desired for distance vision, yet have trouble focusing on print, text, computer or midrange objects closer than your fingertips for extended periods of time.

DISCUSSION:  One of the most common misconceptions about LASIK surgery is that the laser fixes vision problems for good and that there is no need for glasses afterwards for anything.  Over the years if you are nearsighted you undoubtedly have thought how wonderful it is to be farsighted and have fantasized about ridding yourself of eyeglasses and/or contact lenses.  Once you end up farsighted you will realize that farsighted people have their own problems.  When you are nearsighted, you have eyes like magnifying lenses and you can look at the tiniest print and read up close easily; distance is blurry.  When you are farsighted, distance objects are clear yet your eyes tire and strain to perform extended near work like book reading or computer viewing.  Ask your doctor to demonstrate farsightedness by using eyedrops or contact lenses to make you temporarily farsighted before you decide on laser vision correction because it is not uncommon that people end up farsighted.  If you are farsighted and are having Hyperopic (farsighted) LASIK, it is possible you hadn’t worn glasses until later in life and are anxious to get rid of them, yet when all is said and done you may still need glasses for distance or reading.

For people over 40 years old, it is inevitable that after laser vision correction you will need glasses to read and see near objects unless you have MONOVISION laser.  Monovision is when your dominant eye is corrected to focus on distance objects, while the non-dominant eye is corrected for near.  Some people who do not want to wear glasses at all will opt for monovision LASIK.  The authors of TheLaserSite recommend that patient’s over the age of 36 ask their doctors to demonstrate monovision correction with free, trial contact lenses.  It is important to understand that a natural decrease in the near-point focus of the eyes occurs around the age of 40.  Laser close to the age of 40 will correct the distance vision, but problems at near will gradually increase.  If you are under 40, your doctor can demonstrate what your vision at the age of 45-50 will be like.  To do this, the doctor can put drops in your eyes that mimic “over 40” vision, and then can demonstrate how monovision correction will help you to see far and near without glasses or contact lenses post LASIK.  Laser cannot correct the problems experienced at close range that occur after 40.  If you are over 40 and need glasses to see far and take your glasses off to read, when the laser makes you farsighted, your eyeglass needs will flip-flop.  Instead of needing glasses for distance, your distance will be better and you’ll need to put glasses on to read.  Aside from monovision you may choose undercorrection, in which case the laser will bring to around 20/40 for distance (slightly blurry) but you will maintain some near vision

WHAT HAPPENS IF: If you are left farsighted you have the option of wearing glasses, contact lenses, or having an enhancement procedure to correct the difference.

RISK 19: It is possible that you may be left with a film over your vision called “haze” that can last up to 1 year.

DISCUSSION:  Healing haze cannot be controlled for during surgery.  Although somewhat mysterious, healing haze is believed to be the result of the bodies healing process.   The eye responds to the trauma of surgery by depositing proteins underneath the flap that aid the healing process.  You can have 20/20 vision and things can look “hazy” with small amounts of haze.  Healing haze is analogous to having a thin veil over your vision.  Large amounts of haze can decrease your vision as low as 20/60; although rare and getting rarer, healing haze is one of the more common side effects of laser vision correction.  Haze is much more common with PRK surgery and is becoming rarer in LASIK procedures.

WHAT HAPPENS IF:  If you experience haze, your doctor will monitor its progression or regression.  Haze almost always disappears after 1 year, but in most cases it regresses within the first 3 months of healing.  Haze rarely occurs to such an extent as to impede day to day functioning.  Severe haze may be treated with Mitomycin C, .02% eyedrops

RISK 20:  It is possible that you may be left with glare at nightime that takes the form of streaks radiating from light sources or halos around light sources

DISCUSSION:  Negative clearance is when the pupil size exceeds the optical zone diameter of the ablation from lasik. Glare happens after LASIK surgery in people who have pupils that increase in diameter greater than 6 mm in dim illumination if the zone that the surgery is performed in is 6 mm in diameter.  Glare can happen in pupils that expand less than 6 mm, but it is not as common to see this as it is in larger pupils.  Glare that occurs with smaller pupils tends to decrease as the eye heals up to around 6 months after surgery.  It is important to accurately assess pupil size in the preoperative evaluation, and patients with large pupils should be explained the risk of night glare.  To understand glare symptoms better, think of the cornea as a clear dome that vaults the colored part, or Iris, of the eye.  The pupil is a hole in the center of the iris that gets larger in dim illumination and smaller in bright illumination.  The pupil is a regulator of how much light enters the eye.  LASIK surgery changes the curvature of the cornea in a zone with a diameter of 6 mm to 8 mm.  At this writing, 6 mm zones are approved in the USA and 8 mm zones are approved in Canada and elsewhere.  The edge of the 6 mm zone will cause light to bend differently than within zone itself, so if the pupil (which lets light into the eye) gets larger than the zone, light from the edge of the zone enters the eye and causes the glare.


In this diagram, notice the zone of the cornea labeled LASIK ZONE.  This zone is larger than the pupil diameter (in black), so light refracted from the edge of the zone bypasses the pupil.  This patient would not experience glare from the edge of the LASIK zone

In the diagram above, notice the zone is smaller than the pupil, so light refracted from the edge of the zone enters the eye through the pupil and results in glare.  This patient may experience glare from LASIK surgery.  Most glare will reduce for up to 6 months after LASIK surgery.

WHAT HAPPENS IF: If glare happens as a result of LASIK, most of the time it diminishes with time or gets less noticeable.  It is also possible that it may remain for life.  Most patients who have complained of glare say the glare is not much worse than the glare they experienced in contact lenses, however there are patients who suffer from extreme glare at accordig to some reports.  Some suggestions to decrease night glare include night driving glasses, especially if laser is performed for monovision correction, diluted miotic eyedrops at night and retreatment with a larger optical zone.  Driving with a light on in the car may help also, but poses some risk.  Night vision dramatically improves up to 3 months after surgery and can continue to improve for 6 months or longer.  Generally most of the improvement takes place in the first 6 months.  If night glare is present past 6 months, it is most likely permanent..

RISK 21: It is possible that a patient may lose a line of “best-corrected” acuity on the eye chart.

DISCUSSION:  Vision based on an eye chart at your doctor’s office is assigned a ratio such as 20/20 or 20/40 and so on.  If you read the smallest line of most eye charts, you read 20/15.  The next line up is 20/20, then 20/25, 20/30, 20/40 and so on.  Vision of 20/20 is thought of as perfect vision, although many people can be corrected with lenses better than 20/15 vision.  What does the ratio signify?  The person with 20/20 can move to a distance of 40 feet away from a target and recognize it when the person with 20/40 vision must be 20 feet away from the same target before they can recognize it.  If a person has 20/60 vision, the 20/20 person can see from 60 feet an object that the 20/60 person needs to move up to 20 feet to see and so on.  Best-Corrected acuity refers to the best a person’s vision can be corrected with contacts or glasses. Researchers noticed that after PRK and LASIK, the best a small percentage of people post-surgically could achieve on the eye chart was 20/20 even with glasses or contacts where prior to surgery they could achieve 20/15.  These people had lost the ability to see one line on the eye chart.  In the real world, the difference between 20/15 and 20/20 is almost imperceptible. Some people will notice even this slight change in their visual ability.  This can be a problem when a person whose best corrected vision is 20/40 (glasses or contacts do not correct them any better than 20/40).  If they have PRK or LASIK and they lose a line of acuity, they will end up 20/50 and this can affect their ability to operate a motor vehicle, so a patient with best corrected acuity of 20/40 may not be a good candidate for PRK or LASIK.  If a patient has irregular astigmatism (ask your doctor), this may be a contra-indication for the LASIK procedure.  Treatment of significant degrees of irregular astigmatism have resulted in loss of best corrected visual acuity.   If your doctor finds a changing refraction or irregularities on corneal topography, she/he should monitor it and await stabilization before proceeding with the procedure.  Irregular astigmatism may be caused by contact lens use, both hard and soft, incipient Keratoconus (a condition of pathological progressive steepening of the cornea), Pellucid Marginal Degeneration (genetic corneal abnormality), history of corneal surgery, corneal scars or  severe dry eye.  It is more common to lose lines of best corrected visual acuity with PRK surgery than LASIK.

WHAT HAPPENS IF:  There is no way to restore the lost line.  Your eye doctor can refract and try to prescribe as best as possible after LASIK for this problem.  Irregular astigmatism that persists or continues to change is a contraindication for LASIK

RISK 22:  It is possible that a patient may experience dry eyes after LASIK surgery

DISCUSSION:  Eye comfort in terms of dryness is related to the apposition of the eyelid to the surface of the eyeball as well as the presence of the necessary components of the tear layers.  When the eyelids are touching the eye surface with the appropriate amount of tension, they help to spread the components of the tears over the eye evenly moisturizing the cornea and conjunctiva (surface) of the eye.  When the eyelids do not close fully or are altered in some way such as old age or trauma, dry eye syndrome may result.  In LASIK surgery, the curve of the cornea is flattened, so it is possible that an eyelid that previously was in proper apposition to the corneal dome may no longer spread tears effectively over the eye surface because the dome was flattened.  Most complaints of dryness after LASIK surgery decrease with time, however there are reports of people suffering dryness symptoms long after the surgery. If you have dry eyes before surgery and wear contact lenses, if your eyes feel dry only with contacts and are OK without the contacts, you are at less of a risk for dry eyes post-op PRK or LASIK.  If your eyes are dry with or without contact lenses, you are more likely to have dryness after PRK or LASIK.  Most dry eye symptoms resolve over time after LASIK and are treated with artificial tear solutions, specifically Genteal eyedrops, until resolution.

WHAT HAPPENS IF: There are several solutions for the dry eye problem.  Use of preservative-free artificial tears is the first solution.  Genteal eyedrops are not preservative free, but the preservative (Sodium Perborate) breaks down on contact with the tear enzymes, so little preservative is left by the time it comes in contact with the corneal surface.  After a few weeks of using artificial tears, most patients notice a decreased need to continue. If the use of eyedrops isn’t working, the tear drainage system of the eye can be clogged with silicone plugs called punctal plugs.  This painless, non-invasive, non-surgical procedure often helps stop dry-eye symptoms.  There are reports of severe, unresolvable dry eye after PRK and LASIK in rare instances. LASIK is less associated with dry eye problems than PRK.

RISK 23:  It is possible that  a patient may have epithelial ingrowth after LASIK surgery

DISCUSSION:  Epithelial Ingrowth is a condition in which the surface layer of cornea (the epithelium) grows underneath the flap, interfering with healing and vision.  Epithelial ingrowth happens because epithelial cells (skin cells) are dragged by the microkeratome under the flap and sealed beneath it when the flap is layed down.  It may also occur when a flap is cut irregularly, allowing growth to enter under the flap.  Some cells may start to grow underneath the flap, creating a layer of epithelium that interferes with the vision or the healing of the flap-edge.  Epithelial ingrowth is more common in Hyperopic (farsighted) procedures.  If you are farsighted and are having LASIK, request that your surgeon use extra lubrication with Celluvisc eye drops while running the microkeratome.  This has a possibility of decreasing problems related to the flap edge, including epithelial ingrowth.  In the case of epithelial ingrowth, the flap must be lifted, the growth removed and the flap replaced.  In some cases, several flap-lifts must be performed until the growth is halted.  If the growth goes unchecked it can damage or “melt” the flap, resulting in poor vision, scarring of the cornea and haze.  The epithelial cells release the enzyme Collagenase in response to the hypoxic (low levels or no oxygen) environment under the flap.  Collagenase can melt the flap slowly.  Epithelial ingrowth has occured in up to 2% of LASIK eyes, but with new procedural and mechanical improvements, the risk has lessened to less than .5% of cases. Recurrence of the ingrowth occurs in more than 10% of cases and usually occurs 1 week to 3 months after LASIK surgery.  Cases have been reported where ingrowth occurred over 1 year later.

WHAT HAPPENS IF:  Epithelial ingrowth is an annoyance and an inconvenience and most of the time is treated successfully.  If left untreated, the ingrowth can grow throughout the underside of the flap causing flap melt, flap dislocation and loss of flap tissue.  This may have severe consequences visually.  Early identification is the key to successful treatment and TheLaserSite doctors stress regular follow up as recommended by your surgeon or laser clinic.  The flap will need to be lifted and cleaned and followed regularly every week to ensure no regrowth occurs

RISK 24:  It is possible that a patient may have a condition called Lamellar Interface Keratitis (LIK) also called “Sands of the Sahara” after the healing process has begun

DISCUSSION:  “Sands of the Sahara” appear to the clinician as sandy appearing deposition of material in the anterior stroma of the cornea, just beneath where the flap.  Sands of the Sahara is believed to be caused by excessive immune reaction to the trauma of surgery, much like severe haze.  It tends to occur 24 to 72 hours postoperatively.  It tends to occur unilaterally (in one eye) in more than 70% of cases.  It is more common in males than in females.  Other names for Sands of the Sahara include Sands, LASIK Interface Keratitis (LIK), Non-Specific Diffuse Interface Keratitis (NSDIK) or Diffuse Lamellar Keratitis (DLK).  It is interesting to note that multiple simultaneous cases have been reported from certain surgeons and centers.  One of the proposed causes of LIK is  bacterial proteins autoclaved onto the surgical tools encourage an immune response underneath the flap. The autoclave kills the bacteria, but their protein coats remain seared on the instrument and instigate the inflammation under the flap.  Patients may request that the surgeon use disposable instruments to decrease risk of LIK.  Sands occurs in approximately 1/500 cases.  There is also a more severe form that occurs in 1/300 of the 1/500 cases

WHAT HAPPENS IF:  Sands of the Sahara causes temporary blurred vision, mild to moderate burning and stinging, dryness and glare at night time.  If Sands occurs, the patient is put on topical steroid eye drops, and healing can take 2 to 4 weeks, depending on the severity of the inflammation.  Outcomes generally are good after treatment, although vision may be compromised due to the severity of the inflammation

RISK 25: It is possible that you may be left with a sub-conjunctival hemorrage after surgery.

DISCUSSION:   Subconjunctival hemorrage is a benign leakage of a tiny blood vessel under the conjunctiva (thin, transparent layer of tissue over the sclera, or white-part of the eye)  This is caused by superficial pressure during surgery.  Although it may look as though your eye is bleeding, the redness resolves over a 2-3 week period and is of no visual consequence, although cosmesis of the eye may appear undesirable during this period.

WHAT HAPPENS IF:    If you have a conjunctival hemorrage, refrain from taking any aspirin products, as they may make the bleeding increase.  It may be worse upon awakening after sleeping, and it may help to elevate the head slightly during sleep if there is a small hemorrage after surgery.  This will confine the redness to the inferior part of the eye where it may resolve faster or not be as noticeable.  Also, it is possible that cool compresses may help in the resolution of sub-conjunctival hemorrages.

RISK 26: It is possible that LASIK treatment may initiate development of Keratoconus in an otherwise previously healthy eye which may result in need for a Corneal transplant in the future

DISCUSSION:  Keratoconus is a condition where the cornea steepens, gradually taking on the shape of a cone.  The tip of the cone is usually displaced inferiorly and nasally, creating high levels of astigmatism for the patient.  The tip of the cone also may become ectatic (thinner) and ultimately may require a corneal transplant.  In order to safeguard against this, your surgeon will perform a test that ensures a minum corneal thickness post-operatively of at least 250 micrometers.  Before LASIK enhancement surgery, ask your surgeon if you have this has been taken into account.  Excessively steep corneas in some cases scar on the surface due to decreased wetting by the tear film.  This may also necessitate corneal transplantation.

WHAT HAPPENS IF: Should Keratoconus develop, you will be referred to a contact lens specialist who will fit you with rigid gas permeable contacts.  Keratoconics do not see well in eyeglasses, so it will be necessary to wear contact lenses.  The progression of the keratoconus will be monitored closely and in rare cases of corneal scarring, you will be referred to a corneal specialist for a corneal transplant procedure.  It is unknown whether patients who end up with Keratoconus have a predisposition or whether it is caused by thinning secondary to the Laser procedure.  This is extremely rare.

RISK 27:  It is possible that the total optics of the eye’s visual system may be degraded after LASIK surgery depending on patient prescription and corneal curvatures.

DISCUSSION:  The  visual outcome of LASIK surgery is highly dependent on the curvature of your cornea after surgery.  Corneal curvatures can range from extremely flat to extremely steep, and if surgery creates an extremely flat cornea, there can be a degradation in the optics of the eye.  Example:  Extremely flat corneas are measured in diopters and an extremely flat measurement would be between 32 and 35 diopters.  If you have a preoperative eye examination and your cornea curves are found to be 44 before surgery and your prescription is –10.00  (that is –10.00 diopters), your final corneal curvatures will be 34 (44 corneal diopters – 10.00 operative diopters removed).  The outcome is very flat and the patient may experience decreased vision. 

RISK 28:  It is possible that the patient experiences optical abberations following the procedure.  These abberations include blur, fog, flare, soft focus and monocular diplopia

DISCUSSION:  The cornea has a precise aspheric surface prior to LASIK surgery and the flatterning of the cornea can lead to abberations in the optics of the entire visual system.  Blur has been discussed in the Overcorrection and Undercorrection  section and can be treated with eyeglass lenses, contact lenses or enhancement procedures.  Fog occurs when the optical integrity of the cornea is damaged.  The cornea is tightly packed with collagen so little light is scattered within the cornea, allowing for clear transmission.  If the packing of the cornea is disrupted by fluid, debris or swelling, light is scattered and the result can be foggy vision.  Fog generally will regress over time.   Certain lighting can cause the fog to be more apparent, such as a sodium vapor lamp, which emits long-wavelength orange light that is scattered more easily than  a mercury vapor lamp which emits blue, short wavelength light.  Flare is caused by the pupil margin being larger in diameter than the ablation zone (see section on GLARE risk)  Flare can be eliminated by constricting the pupil so it is within the optical zone of the surgery.  Surgeons are developing masking methods and topography assisted lasers to help smooth out treatment zones and decrease the risk of flare and glare.

 Asphericity of the cornea allows for no increase in spherical abberation as the pupil expands.  When the asphericity is altered as it is in LASIK, the decreased asphericity can cause light to be focused at different points not coincident with the retina..  This results in soft focus under low-light conditions, where images seem to have a slight fuzziness or decreased sharpness in conditions of low light.

When the pupil is larger than the optical zone and lighting conditions are just right (usually at night looking at a bright object), two retinal images can be formed, one being the normal corneal image and the other caused by defraction of the edge of the optical zone of the surgery.  Bi-refraction as it is called can cause monocular diplopia (double image in one eye).  This can also appear as image ghosting.  If the surgeon increases the optical zone and creates Positive Clearance (see Negative Clearance: Risk of Glare section), this can improve on the image ghosting problem.  However,  this also necessitates incresing depth of the original ablation and may cause  other optical aberrations or undesirable corneal thinness.

Scanning lasers that use minimal transmission multi-zone technology can help to reduce depth of ablation zone while increasing the available optic zone.  Scanning lasers can increase the optic zone to 10 mm in some cases, reducing risk of optical aberrations.

EXCIMER LASERS: TECHNICAL SPECIFICATIONS

Conventional laser surgery uses a full-area, broad beam laser system.  Flying spot Scanning laser systems have certain advantages over broad beam systems.  In these systems, software directs the X and Y axis scanners and controls small diameter laser spots to remove material in a pattern that produces the desired profile.  For myopia, the system would make a series of overlapping laser shots in a spiral out from the center of the cornea.  As the spiral expands, the software reduces the number of pulses per position, reducing the amount of material removed at each position.  This laser produces a smoother corrective profile.  Broad Beam laser systems have uniform beam intensity and energy levels of 100 to 200 mJ/cm2 at low repetition rates (10 to 50 Hz).  Flying spot scanning laser systems use beam diameters between 1 and 2 mm with a typical treatment requiring several thousand shots at 50 to 200 Hz.  A benefit of scanning systems is their ability to correct non-spherical corneal irregularities such as astigmatism in which the axes are not orthogonal.  This technology enables smoother, more accurate profiles, so it is even more important that surgeons consider other irregularities in the anatomy of the eye when using the laser.  Future technologies will account for optical aberration not only from the anterior surface, but also from the posterior surface of the cornea, the anterior chamber, the lens, vitreous and retina of the eye

Each pulse of excimer UV energy possesses 6.4 eV which has the ability to cleave 3.5 eV carbon-carbon bonds.  Excimer UV light energy has a wavelength of 193 nm.  The excimer, short for excited-dimer, consists of an inert gas and a halide (usually flourine).  These are excited to higher energy states by subjecting them to thousands of electron volts.  Lasers have beams that are either homogenous, gaussian or reverse guassian.  A homogenous laser is one in which the beam profile is flat; a guassian laser is one in which the center of the beam is deepest and the depth decreases in a guassian fashion towards the periphery of the beam, and a reverse guassian has the deepest profile toward the periphery, getting more shallow toward the center of the beam in a guassian distribution.  Fluence is a measure of the rate of ablation of corneal tissue.  For excimer laser refractive surgery, fluence must be above 50 mJ/cm2  and has the same effect on corneal tissue up to 120 mJ/cm2.  Fluence increase is directly related to beam quality increase due to increasing beam homogeneity.  Increased fluence is also associated with increased laser-shockwave effect, decreased optics of ablation and increase in thermal energy delivered to the cornea.  Fluence is directly related to quality of the laser gas and voltage of the laser.  The ablation rate of most excimer laser systems is .25 microns per pulse. 

Most excimer lasers are class IV lasers.  Class IV lasers are defined as a laser with a wavelength from 180 to 400 nanometers and a pulse energy greater than 0.38 mJ in less than .25 seconds. For instance, the Visx STAR excimer laser system will fire with a pulse energy of 45.2 jJ at a rate of 5 pulses per second.  It can therefore fire a maximum of 2 pulses in a .25 second period for a total output of 90.4 mJ in that period. 

MPE = Maximum Pulse Energy

MPE/pulse = (3 mJ/cm2) / (2700) = 1.1 microJoule/cm2
(2700 assuming 10 surgeries a day and 270 pulses per procedure)*
*these numbers for VISX STAR laser only; others may vary

Surgical Formulae:

There needs to be an unviolated base of Cornea underneath the flap of at least 250 microns thickness post-operatively.  Flap thickness is approximately 160 microns, so a residual 410 microns has to be left on the cornea post-operatively for maximum visual results.

On a Cornea with a 6 mm Optical zone (U.S.), 12 microns of tissue are removed per diopter of power needed, so if your correction is –4.00, 48 microns of tissue may need to be removed. Pachymetry is the measurement of corneal thickness.

Pachymetry - 410
  12 mic/diopter

this formula tells you how much cornea you are safely able to  treat with a 6.0 Optic zone (standard only in the US).

Munnerlyns Formula – tells the surgeon how deep of an ablation to create.  The depth of the ablation increases exponentially with the square of the optical zone size

Depth of Ablation = diopters of correction X ablation diameter squared
                                                                      3

Masking

Masking is used by a surgeon to achieve a desired custom ablation of the cornea.  A mask of a certain curvature or shape is placed over a segment of the cornea so the laser affects the adjacent areas differently than the masked area.  The mask can be erodable and may be made out of silicone, plasstic or a biomaterial, so the laser gradually erodes certain parts of the mask more than others and the ablation result is a gradual change along the masked area of cornea.  This is useful for blending the optical zone of the surgery creating a smoother, better transition of the periphery and lessening risk or symptoms of flare and glare.  Topography-Assisted Lasers allow the ablation to follow the peaks and valleys and asphericity of each individual cornea based on the corneal topography.

THE LASERS

This section is to be used in conjunction with the section Broad Beam vs. Scanning Lasers. That section describes the differences between the major types of lasers. 

NIDEK EC 5000

Creates the smoothest pattern available underneath the flap. Scanning slit technology, slit size 2 X 9 mm.  The slit oscillates and rotates, creating a smoother surface.

LASERSITE LSX

Uses a scanning spot, .8 to 1.0 mm.  Has an active and passive tracking system (SX) which follows subtle eye  movements and decreases chance of decentered ablations  The LASERSITE LSX is the smallest laser in the world at this writing.

Bausch and Lomb Technolos 217A

Formerly the Chiron Technolas, this laser uses a scanning spot 2mm in diameter.  It is ergonomically desirable and as such, the laser of choice for many surgeons.  This laser is not available in the US currently and is used mostly in Canada.  The ablating transition zone used with this laser extends the true optical zone from 6 mm out to 8 or 9 mm.  This is advantageous in surgeries involving large pupils or high levels of astigmatism.  There may be a decreased risk of glare at nighttime with the B & L 217 A.

Autonomous

Uses a scanning spot less than 1.0 mm (800 micrometers) in size and LADAR tracking         to follow the pupil as it moves.  LADAR is a military technology that was applied to the excimer laser.  Autonomous has the ability to provide topography-assisted customized ablations.  The laser lases in a manner that the next laser pulse avoids traveling through the plume of the previous pulse and as also eliminates occurrence of central islands.  The pupil of the patient must be dilated for this laser.

Visx Star S2

Scanning Spot 1.2 to 6.5 mm in diameter

Summit Apex

The top laser for correction of hyperopia (farsightedness).  Ablatable disc allows for custom ablations.  Uses Axicon lens for better hyperopic transition zone

Baush and Lomb Orbscan Topolink

The future of lasers includes topography-assisted lasers; lasers that are guided by the patients corneal topography.  This results in a customized ablation.  This particular laser will use wavefront technology to measure the total optical aberration of the eye and account for differences in internal curvatures and powers in it’s ablation.

Technomed

Another laser that utilizes the Dresden Wavefront Analyzer

Wavelight

WHAT TO REASONABLY EXPECT FROM LASER VISION CORRECTION

It is important to know what to reasonably expect from PRK and LASIK vision correction.  If you expect to lose dependence on vision correction devices such as contacts or glasses and don’t expect 20/20 vision, you may be pleasantly surprised.  There is no way to predict the outcome exactly, but most people achieve vision of 20/20.  Think of 20/20 vision as a very pleasant side effect, which happens most of the time.   You may reasonably expect to be able to operate a motor vehicle without correction, wake up and see your alarm clock, get in and out of the shower, go to the movies, all without need for contacts or eyeglasses.  It is possible that you may want the vision a little sharper and may use a very thin prescription for night driving or tweaking the vision to 20/20, but go without glasses and contacts most of the time.   Refer to DATASITE web link for statistics on visual outcomes.  There have been instances where people have regressed to their original prescription and, although uncommon, this is a possible outcome.  Fortunately, you have the option of an enhancement if medically feasable, you can wear contacts or glasses after PRK and LASIK

Do not expect your newly corrected vision to remain stable forever. PRK and LASIK surgery is very effective at reducing your prescription, but it will not stabilize your vision over time.  Your vision may change in the ensuing years, but you most likely will never regress anywhere near your original prescription.  Ask you post-operative doctor to prescribe glasses after surgery to decrease eyestrain for nearwork and computer use, a common cause of nearsighted regression in young patients.

HOW CAN I TELL IF I AM A LASIK CANDIDATE?

The most important consideration for candidacy is a thorough understanding of  all the risks of LASIK.  LASIK is an elective procedure.  If you choose not to have LASIK, it is unlikely that any risks of LASIK will happen to you.  If you elect to have the procedure, you accept all the risks and as long as you understand them you may be a good candidate.  You also must have reasonable expectations.  The purpose of Laser Vision Correction is to reduce or eliminate your dependence on prescriptive eyewear.  Think of 20/20 vision as a very pleasant side effect that happens most of the time.  No one can guarantee 20/20 vision, so reduction or elimination of dependence on prescriptive eyewear is a more realistic expectation than 20/20 vision.  If your expectations are realistic, you are one step closer to being an ideal Laser Vision Correction candidate. The final determination is based on the parameters of your eyes.

If you are Myopic (nearsighted) the laser can correct:
Up to 15 diopters of myopia
Up to 6 diopters of astigmatism
Recommended pupil size less than 6 mm, although this does not limit candidacy

If you are Hyperopic (farsighted) the laser can correct:
Up to 5 diopters of hyperopia, possibly 6
Up to 3 diopters of astigmatism
Anterior Basement Membrane Dystrophy is a contra-indication

Astigmatism – Up to 8 D of astigmatism can be corrected for.

HOW LONG BEFORE LASER VISION CORRECTION SHOULD YOU STOP WEARING CONTACT LENSES?

While many doctors differ in their procedure as when to discontinue contact lenses before Laser refractive surgery, a recommended conservative schedule is as follows:

Soft lenses:  At least 10 days
Soft Astigmatism lenses:  At least 2 weeks
Rigid Gas Permeable or Hard lenses:  6 weeks for every 10 years of contact lens wear.

THE PROCEDURE ITSELF – THE EXPERIENCE

Patients who wear soft contact lenses should be out of the lenses for 1 to 2 weeks prior to surgery; the longer the better.  Patients who wear hard or gas permeable contact lenses may need to be out of lenses for 4- 6 weeks or more.  Ask you doctor her or his recommendation.  Your doctor will perform a preoperative PRK or LASIK evaluation where your vision will be tested with and without cycloplegic eyedrops.   The health of the front and back of the eye will be examined, you will be educated to the facts as the doctor sees them and you will be given a consent document to review.  The consent document will be presented to a staff member at the laser center.  The staff member will review the consent document to make sure you fully understand risks and have reasonable expectations.  Once it is signed, the patient is escorted to an examination room.  Pretesting is performed with Corneal Topography, Auto-refraction and pacymetry (testing of corneal thickness) A surgical cap is donned and antibiotic eyedrops are given 2 or 3 times.  The surgeon should then come by and speak to you briefly, review the records and make sure everything is in order.  They will then escort you into the laser suite and you are laid down on the surgical table.  While you wait, the surgeon and assistant check and recheck the laser to insure it is functioning at the desired level.  The surgeon may demonstrate some of the sounds and sights that you will experience so there will be no surprises and you may request this.  The surgeon will then place a patch over one eye and instill a drop of anaesthetic in the other eye.  The surgeon may also instill more antibiotic drops at different points during the surgery. When the anaesthetic starts to work, the surgeon will insert a thin, metal device in between your lids to hold them apart during surgery.  This device is the lid-spreader.  Above you you will see a red light, not unlike the color of the display on an alarm clock.  The surgeon will ask that you hold very still and look at the red light and will use a surgical marker to mark your corneas with a water soluble ink called Gentian Violet.  The markings assist in lining up the microkeratome (lathe) that is used to make the flap and to ensure that at the end of the procedure the flap is laid down in the proper orientation.  A drop of balanced salt solution is placed on the eye.  The suction device will then be placed on the eye and you will hear a drone-like motor which is the suction of the microkeratome onto the eye.  As the microkeratome suction occurs, your vision will dim and may go black temporarily.  The surgeon then tests the pressure of the eye to make sure the microkeratome is firmly in place and to make sure the eye pressure isn’t too high, then the surgeon steps on a foot pedal and the patient hears a whirring noise.  The whirring noise is the mircrokeratome lathe as it runs across the eye making the flap.  The microkeratome is removed after the flap is created and your vision comes back, albeit blurrier.  The patient is now asked to look at the red light up above.  The surgeon takes a surgical tool and lifts the flap back.  The surgeon then drys off the surface of the exposed cornea.  The surgeon then lines up the laser with the area of the cornea to be lased and when the patient is fixating appropriately, steps on the foot pedal and starts lasing.  The laser sounds like a clipboard banging on a table top.  (click here for link to view a video clip of the patients view)  CLAK! CLAK! CLAK!  The sounds are the acoustic energy of the laser breaking the molecular bonds on on the exposed corneal stroma.  The surgeon will coach the patient through this, instructing them to keep their head and eyes still and look at the red light.  Often there is a sulfur-like smell that emanates as the laser evaporates the tissue within the cornea.  When the appropriate power has been lased, the surgeon washes underneath the flap with balanced salt solution as she/he lays it down.  This is to remove any debris that may be left on the interface between the flap and the lased surface. 

After manipulating the flap to insure it is resting properly, the surgeon removes the lid spreader, asks the patient to blink a few times to insure the flap is suctioned down.  More balanced salt solution may be applied at this time.  After words the flap is tested for stability, the eye is patched and the other eye undergoes the same procedure.  After both eyes have been lased, the patient sits up off the table and often is able to see across the room right away!  The patient is given some more antibiotic eyedrops and possibly anti-inflammatory eyedrops and asked to sit with their eyes closed for 20-30 minutes.  They then are given sunglasses and can go home.  Sunglasses are recommended over eye patching by most surgeons.  Patches can be used to protect the eye at bedtime for the first 3 or 4 nights while sleeping. That evening, there may be slight dryness or discomfort, but over the counter analgesics can help and it is wise to get bed rest for several hours.

CHOOSING A SURGEON

By now you have a thorough understanding of the surgical process of Laser Vision Correction.  Do not choose surgery just from an advertisement and walk into a clinic and have it done.  Find a reputable clinic; one a friend or family member recommends.  Choose surgery from someone who a doctor you trust recommends.  Your referral doctor should be someone you are comfortable with and trust to guide you through the process smoothly and efficiently and to ensure you receive the best surgical care available from the surgeon and the laser clinic.  The learning curve for a surgeon is approximately 1000 eyes, not 1000 patients; that equals 500 patients (2 eyes per patient).  When you ask doctors how many surgeries they have done, be sure the number you get is LASIK surgeries.  If they tell you they’ve done 10,000 refractive procedures, they may be including cataracts, corneal transplants and other refractive surgeries that have little bearing on their expertise with the LASIK procedure.  Ask for the amount of LASIK procedures they have performed.

THE HEALING PROCESS

The most important visit of the post-operative period is the one-day visit.  During the visit, your post-operative doctor will evaluate the sealing of the flap, the formation of haze (rarely formed at 1 day), edema (fluid in the cornea), interface debris (dust and particulate matter left over from the surgery that was trapped under the flap), post operative vision and corneal curvature.  Edema is very common at 1 day and may be the cause for slight blurriness at this point.  Edema recedes rather quickly during the first week and this is the cause of shifting vision during this time for some people.  Often there may be a red spot on the white part of the eye.  This benign breakage of a blood vessel may occur due to the trauma of the surgery or the stress that the eye is under during surgery, but it will resolve within a week or two.

POST OPERATIVE VISITS

WHAT TO DO AND WHAT NOT TO DO DURING YOUR FIRST WEEK POST-OPERATIVELY

Don’ts:  
You may not rub the eye for any reason whatsoever
You may not wear eye makeup: foundation is fine, but try to keep it away from   the eyes
You may not go swimming
Do not bend over and lift heavy objects
You must avoid strenuous exercise
You may not not put anything in your eyes that was not prescribed for the post-op period
Do Not Squeeze your eyes or put pressure on your eyes.

Do’s   
You may shower and get your face  wet

You may gently wipe your eye lids with a soft tissue

Make sure you take the drops prescribed in the first week as directed

WHAT TO CONTACT YOUR POST-OPERATIVE DOCTOR FOR IMMEDIATELY IF IT OCCURS:

SHARP PAIN THAT LASTS LONGER THAN 30 SECONDS IN ONE EYE
SUDDEN ONSET OF VERY BLURRY VISION IN ONE EYE THAT LASTS MORE THAN 30 SECONDS

THE ONE WEEK VISIT

This visit is important because it is the first time the eye pressure will be checked post-operatively.  During the LASIK procedure, the eye is subjected to a very high pressure in order to make the flap.  It is important to make sure the pressure returns to normal to prevent damage to the inside of the eye.  The rest of the visit is to assess what was assessed at the 1 day visit.  Typically if haze is going to be present, it has started to show itself at the one week point.  A refraction to assess vision prescription is performed also.

THE ONE MONTH VISIT

Everything performed at the one day and one week visit should be performed at the one month visit also.  At one month, the doctor has a pretty good guess as to what your vision will heal to, but there can still be significant shifts and changes due to edema and haze.

THE THREE MONTH VISIT

Except for rare cases, vision is stabilized at the three month visit.  Prescription, eye curvature, pressure and evaluation of the cornea are performed. Final evaluation of acuity (ie 20/20, 20/30, 20/40 etc.) is performed.  If there is residual blur left over, the doctor may offer the option of enhancement surgery to be performed at this time.

THE SIXTH MONTH VISIT

The sixth month visit is a maintenance check up to ensure everything is going smoothly and the patient has no significant complaints or findings

THE ANNUAL EXAMINATION

The annual examination and future annual eye examinations are important.  Your doctor must follow you to insure your vision does not regress or that any of the rare complications that can happen 1 year or more post-operatively are not happening to you.  Your doctor will dilate your eyes and check for retinal thinning, tears or holes that can lead to retinal detachment.  Your doctor can also make recommendations to delay or slow down regression or help you to determine if an enhancement surgery is in order.