Eye and Vision Care Glossary
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Aberration (ab-er-a-shun)
Failure of light rays from a source of light to form a perfect point image after going through optical elements of a system. Aberrations may appear as skewed images, blurry or double images, images with a tail like a comet or appear as halo-like rings. They types of aberration are Chromatic, Distantial, Longitudinal, Marginal, Meridional, Monochromatic, Spherical, Aspheric, Coma, Astigmatism and others at higher orders.
Aberrometer (ab-er-ah-meter)
A machine designed to measure the aberrations in an optical system. The first technology designed to measure aberrations was designed for a telescopic system by Hartmann and Schack and is known as the Hartman-Shack aberrometer. Many more aberrometers are now available and improvements in the field of aberrometry have led to advancements in optics throughout many fields including telescopy, microscopy, ophthalmology.
A-beta-lipoproteinemia
Autosomal recessive disease where gene for synthesis of beta-lipoprotein is absent. Can lead to pigmentary changes in the retina and cataract – symptoms may include flashing lights in peripheral vision, night blindness, glare and blurry vision.
A.B.O
American Board of Opticianry; American Board of Ophthalmology
Accomodation (a-komm-uh-da-shun)
Accomodative
Inside of the eye there is a physiological lens that is clear unless a cataract develops. The physiological lens is attached to a musculature known as the ciliary body by circumferential threads known as zonules. The physiological lens changes shape as the muscle acts to tighten or loosen the zonules, which in turn changes the shape of the physiological lens in response to the distance at which objects are viewed. For instance, when viewing objects at distance (greater than 20 feet or 6 meters) the ciliary body relaxes, the result of which causes the zonules to tense and pull the physiological lens to it’s flattest state, it’s natural state being rounder. When the ciliary body contracts in response to the object being viewed approaching the eye (getting closer), the zonules loosen and the physiological lens approaches it’s normal, more spherical shape, which adds power to the optical system of the eye allowing for focus at near. From the age of 11 on, the physiological lens gradually hardens and, around the age of 40, is sufficiently hardened so that the ciliary mechanism starts to loose it’s ability to alter the shape of the lens, leading to Presbyopia, commonly known as “bifocal” age.
Accomodative-Convergence
Muscles responsible for altering accommodation via the ciliary mechanism are tied into muscles responsible for turning the eyes inward. As we look from distance to near, our eyes must turn inwards to the point of focus at near, and when we look back towards distance, the lines of sight, hence the eyes, must become more parallel to one another. Accomodation does not occur without convergence of the eyes and convergence of the eyes does not occur without an effort to accommodate.
Accomodative Excess
Excess focus directed at a near point stimulus. The system of the eye over-accomodates which can lead to trouble refocusing at distance, headaches, eyestrain and distance blur
Accomodative Insufficiency
Inability to adjust the accommodative system sufficiently to focus in on a near point target. When looking from a distance to a near point such as book text, there may be a slight delay in the ability of the accommodative system to clear the print. Can lead to eyestrain, headaches and blurry near vision.
Acetazolamide (A-seat-a-zol-amide)
Also known as Diamox. An agent used to lower the pressure within the eye, specifically used for cases of acute attacks of glaucoma
Achromatopsia (A-kroma-tope-sia)
Total color blindness. Very rare
Acuity, Visual
Detail, sharpness or acuteness of vision. As light travels through the optics of the eye, optical elements bend it and shift it and focus it towards the retina. If the power of the eye is equivalent to the distance the light has to travel to focus to a “point” on the retina, the best acuity is achieved. If the power is weak, the light focuses at an imaginary point behind the retina and if the power is too strong the light focuses at a point in front of the retina. Focus anywhere other than exactly on the retina diminishes visual acuity.
Adducens Oculi
The Internal rectus muscle
Adduction
The rotation of the eye toward the midline (nasally)
Adenokeratoconjunctivitis
Pink eye, also known as conjunctivitis, caused by a virus from a class of viruses known as the adenovirus. Usually transimitted via upper respiratory infections such as the common cold.
Adie’s pupil
Adie’s syndrome
Afferent Pupillary Defect
Inability of the pupil to respond to light directly shone upon it. Dependent on the neurosensory connection of the pupil to the midbrain.
Age Related Macular (Mack-You-Lar) Degeneration (AMD)
A condition in which the area of the eye responsible for central vision, the macula, becomes damaged, leaving people with a blind spot known technically as a “scotoma” within the persons line of sight that overlaps everything they look at. Moderate to advanced AMD results in the inability to recognize peoples faces, read text, thread a needle and other activities that make it difficult to function when attempting to discern detail. Several culprits for AMD are suspected including (1) genetic predisposition (2) accumulation of proteins, lipids or calcific deposits within the macula (3) accumulation of VEG-F protein (4) exposure to ultra-violet radiation over time (5) eye surgery (6) weakening of vessel walls within the choriod (the layer of blood vessels immediately underneath the retina and macula or (7) weakening of the basement membrane known as Bruch’s membrane that separates the choroids from the sensitive retina and macular area. Two types of AMD exist; Dry AMD and Wet AMD. Dry AMD is responsible for 90% of all vision loss related to AMD and is a less severe form of the disease. Dry AMD is responsible for damaging vision from between 20/60 to 20/150 in the majority of cases. Wet AMD is more devastating and can lead to central vision impairment of 20/400 or worse. Treatments for dry AMD do not exist although one company, TLC Vision, is developing a technology known as Rheopheresis (Rheo Therapy) that has shown some benefit in clinical studies. Treatments for wet AMD focus on blocking the VEG-F protein and some such as Macugen and Lucentis have shown some promise at halting the progression of the disease at the time this glossary was written. Lucentis has actually been shown to restore some vision in patients who have suffered severe vision loss from wet AMD. Many more therapies are being developed, including optical therapies that will be able to restore some useful vision after the progression of the disease is halted. These include the Implantable Miniature Telescope (IMT - Vision Care Ophthalmics) and LiquiLens Intra Ocular Lens for Treatment of AMD (Vision Solutions Technologies). By the time this glossary gets published the IMT will be to market. The IMT is a device that provides improvements for some people with advanced disease for distance vision. LiquiLens will be entering clinical trials within 12 months and is a device that improves reading vision in people with AMD.
Agnosia
Total or partial loss of the ability to perceive/recognize objects
Alcaine
Proparacaine HCl. Eyedrop used to numb the cornea or surface of the eye
Alexia
Inability to understand or recognize the written word.
Amaurosis
Amaurosis Fugax
Total blindness that occurs as a result of an event within the visual system, not a change in the eye itself.
Amaurosis, Leber’s Congenital
Recessive hereditary disease where partial or complete blindness occurs. Thought to be a defect in the mitochondria of the retina, specifically the central retinal region known as the macula.
Ambermatic
Lenses that change shade from amber to dark grey as one moves from overcast or dark environments to lighter environments respectively
Amplitude of Accomodation
The ability to accomdate is known as the “amplitude” of accommodation and as we age, our “amplitude” of accommodation decreases linearly
Amblyopia (am-blee-ope-ia) a.k.a. “Lazy Eye”
A condition in which signals from the eye to the brain are interrupted and unable to provide the full cadre of impulses that usually would allow for perfect vision. The interruption can be in the retina, the optic nerve or within the brain itself and may be due to uncorrected or high vision errors such as farsightedness or astigmatism, an idiopathic congenital or pathological physiological defect in the optic nerve, an eye turn where one eye is underused because of an opacity within the optics or a strabismus (eye turn i.e. crossed-eyes or uncrossed-eyes). An amblyopic eye can be corrected in most children if caught early enough. Studies show that it is best to correct an amblyopic eye before the age of 7, although it can be corrected later. Methods of correction include eye patching the good eye for various periods of time, pharmacological patching where eyedrops are used to blur the good eye so the patient is forced to use the poor eye, surgery to straighten the eyes and get them working together, or vision therapy. Adults with amblyopic eyes are unlikely to get much benefit out of these methods of correction although studies
American Academy of Ophthalmology
Association of board certified ophthalmologists.
American Academy of Optometry
Professional organization for optometrists started in 1922. Provides certification for optometrists who complete advanced training above and beyond graduate degree (O.D.) and residency training.
American Association of Ophthalmology
Founded in 1956 which merged into the American Academy of Ophthalmology in 1981
American Board of Ophthalmology (ABO)
Founded in 1916 – determines adequacy of training, professional preparation and competence of ophthalmologists who seek to be certified as specialists.
American Board of Opticianry
Accreditation and licensure organization for opticians. Founded in 1947
American College of Optometric Physicians
Founded in 1978 to promote various educational measures and encourage involvement of optometric practice in the diagnosis and management of various eye pathologies.
American Ophthalmological Society
Formed in 1869 – high requirements for membership including excellent professional performance and adherence to the highest ethical standards in ophthalmology.
American Optometric Foundation
Founded by optometrists to support the advancement of vision care through research efforts and education.
American Optometric Student Association
Ametropia
The state of the eye in which, with the lens and accommodative mechanism of the eye relaxed, light rays entering the eye are not focused exactly on the retina
Amplitude of Accomodation
See Accomodation, Amplitude
Amsler Grid (amz-ler)
A square grid of straight lines printed on paper or cardboard with a fixation point dead center. If a doctor notices a finding within the retina, most likely close to or within the macula of the eye, he/she may recommend use of this simple home screening so a patient may assess the function of the retina over time. A positive Amsler Grid test occurs when while fixating on the center fixation point of the grid, the lines or any part of the lines around the fixation point or elsewhere on the grid appear distorted, bent, broken or missing. The test is performed with each eye individually occluding the non-tested eye and at 14 inches infront of the face. Amsler grid is a good way to follow changes in the macula of the eye and a positive test (indicating any change in the appearance of the grid since the last test) should be reported to an eye doctor immediately. Blurred lines or double lines do not constitute a positive test and the test should not be performed with progressive “no line” bifocals as there may be false positive distortion due to the optics of the lenses – also be careful not to look through the line of a bifocal – either top of the bifocal or bottom will produce a more accurate result.
Angiogram , Flourescein (an-jee-ogram)
(Angiography, Flourescein)
(Angiography, Ocular)
Method of viewing vascular abnormalities within the retina of the eye. Flourescein is injected through the arm vein and as it courses through the blood vessels of the eye, photographed with a system sensitive to fluorescence. The result is a series of photographs or video displaying the blood flow throughout the retina and areas where vessels may leak, have formed new networks or have specific defects.
Aniridia (an-i-ridia)
Complete or partial absence of the iris, or colored part, of the eye
Aniseikonia (an-ice-i-cone-ia)
Unequal image sizes – if the visual angle of a particular image being viewed differs between the two eyes (ie one is larger than the other), the two eyes may have difficulty merging the image seen from both eyes individually at the optic chiasm. This may result in double vision or, more likely, suppression of the image provided by one eye or the other.
Anisometropia (an-ice-oh-metro-pia)
Unequal prescriptions in one eye as compared to the other. More frequently used to refer to a difference in refractive error between the two eyes greater than 1 diopter. Too great an anisometropia may result in double vision or, more likely, favoritism of one eye over the other and suppression of the image in the non-favored eye.
Ankyloblepharon (ankle-o-blefaron)
Paritial or total adhesion of the eyelids to one another
Aphakia
A condition in which the physiological lens of the eye is removed and not replaced with a synthetic intra-ocular lens. This condition is rarely congenital and is usually caused by removal of a cataractous physiological lens.
Aplanatic
An optical system free from optical distortions such as astigmatism, coma and higher order aberrations.
Arcus
(Arcus Senilis)
Abnormal deposition of one or more serum triglycerides anterior to the limbus of the eye. The limbus is the junction where the conjunctiva and sclera come together and meet the cornea of the eye. The cornea, being an avascular tissue may have serum triglycerides that “leak” into it from the vasculature surrounding the cornea, usually the choroids or vessels within the plexus of vessels that serve the sclera and conjunctiva. This creates the appearance of an annular deposit around the cornea, kind of a white-gray ring that indicates to an eyedoctor the patient may have high serum triglyceride levels of one kind or another.
Arteritis, Temporal
A disease of unknown etiology wherein there is widespread inflammation of the arteries, particularly those of the temporal arteries Vision may be temporarily or severely impaired as a result of an occlusion from these arteries that enters the retinal vasculature, similar to a stroke of the eye.
ARVO
Association for Research in Vision and Ophthalmology
Aspheric
Not spherical; similar to a section of a cone or a three-dimensional parabola. The true shape of the cornea of the eye is aspheric. Aspheric optics assist in decreasing spherical aberration responsible for nighttime glare and other optical degradations.
Asteroid Hyalitis
(Asteroid Hyalosis)
Opacities of calcium soaps occurring within the vitreous body (central part) of the eye – usually age related. More frequently found in males and not associated with any pathological condition. Usually unilateral although cases have been found where they are bilateral.
Asthenopia (Ass-then-opia)
Term used to describe eyestrain.
Astigmatism
A condition in which the optics of the eye are such that rays that enter are not focused at any one particular point, usually the result of having a stronger “bend” in the optical system in one meridian than the other. An eye without any astigmatism would have a front-surface shaped something like a slice off a round ball such as a basketball. In an eye with astigmatism, the front-surface would be shaped more like a slice off a football, where one meridian is a steeper curve than the other meridian, each meridian causing light to focus at a different point than the other. The steeper meridian would focus further from the retina while the flatter meridian would focus closer or behind the retina as it is a weaker curve.
Astrocytoma
Tumor of the central nervous system derived from glial tissue, specifically astocytic glial tissue, often occurring within the retina. Successfully treated surgically.
Atropine
Belladonna alkaloid (poison) with action as a dilating agent (mydriatic or cycloplegic) in it’s sulfate form. In the eye it paralyzes the pupil sphincter muscle responsible for shrinking the pupil by blocking the effects of acetylcholine within the parasympathetic nerves of the pupil. This allows for a pharmacological expansion of the pupil parameters enabling clinicians to gain a better look inside the eye.
Autorefraction
Automated method for standard refractions. Objective measure of refractive error where clinicians subjectively determine refractive error by substituting a series of lenses in a standard refraction.
A/V
Abbreviation for “arteriole to venule diameter”.
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