There are many contributing factors around how our eyes develop, change and adapt over time. In this article, we will discuss how myopia (nearsightedness) develops, how it evolves over time, how extended periods of close work (focusing on near objects) can intensify myopia into adulthood, and what can be done to lessen its effects.
Development of Myopia Over Time
Myopia: How It Develops
Myopia, also known as nearsightedness or short-sightedness, is one of the most common eye conditions in children and adults, affecting approximately 42% of Americans, up from 25% in 1970.
Myopia is characterized by the ability to focus on objects up-close while struggling to see things far away. The reason for this focus error is the shape of the eyeball: as the eyeball develops and grows, it either becomes elongated or the surface of the eyeball becomes too steep, making the focal point land in front of the retina. Myopia is thought to be progressive, often worsening over time.
Myopia Peaks At Adulthood
Although classified as a progressive condition, the development of the visual system (including the eyeball) is normally complete by adulthood. This means the curvature of the eyeball that causes myopia is completed - it will not worsen or become more elongated at this point. Changes in distance vision should not continue to progress on a regular basis (excluding astigmatism) after the development of the visual system is completed through natural growth
So then, logically speaking, myopia should not get progressively worse as we enter our adult years. But prescriptions are increasing both in strength and frequency. What is the cause? There must be additional factors at play.
To further understand, let’s review how our eyes work. More particularly, how our eyes focus on near objects as opposed to far.
The Near Reflex Triad
The Near Reflex Triad is the process the eye takes in order to adjust and fixate on a near object. The Near Reflex Triad is made up of three functions: Accommodation, Convergence and Divergence.
Accommodation is the process of adjusting focus for viewing near objects. Viewing distance objects differs from looking at near objects in how the musculature of the eye adjusts the focus mechanism, called the Lens. When viewing distance objects (objects greater than 20 feet or 6 meters from our eyes), the eyes are aligned straight ahead and the line of sight of each eye is approximately parallel to one another. Light from the distance target enters the eye and is focused on the retina, or light -sensitive tissue on the back of the eye. When looking from a distant target to a near target, the eyes must change focus.
The eyes must also turn in towards each other to bring proper focus onto the near object, in a process called Convergence. This change in focus only occurs when looking from distance to near. When looking up from near work, or near to distance, the eye un-focuses (releases Accommodation) and the eyes straighten and the lines of sight go from being converged on a near target to being parallel again.
The process of going from a position of convergence (looking at near) and Accommodation (focusing at near) to being straight and unaccommodated for distance viewing is called divergence.
How They Work Together
The processes of convergence and divergence are controlled by the musculature surrounding the eye. These muscle actions for convergence and divergence are intertwined with the muscle that controls the focus for the lens of the eye so when the eye converges, the eye muscle focuses the lens for near and when the eye diverges, the eye muscle unfocuses the lens for distance. The eye muscles receive information for when to converge or diverge, direct the eyes to the left, the right, up or down based on information shared between the retina (image positioning information) and the nuclei (eye movement information).
If an object passes to the left of you, the image of the object will fall on an area of the retina that corresponds to your left side. The nuclei will receive this signal and relay another signal to the eye muscles to look left in order to move the image of the object towards the area of the retina where the image is best viewed. Muscles inside the eye then control the process of Accommodation and Unaccommodation. When the act of focusing occurs, the mind assumes that a near object is to be viewed and convergence action kicks in.
Simply stated, there is no convergence without Accommodation and no Accommodation without convergence. There is no divergence without Unaccommodation and vice-versa.
Factors That Can Lead to Myopia Progression In Adulthood
So now we know:
- How the Near Reflex Triad works; and
- That the visual system is fully-formed at adulthood.
So then how does the worsening of myopia continue into adulthood? There are 2 possible reasons, both of which are functions of close work.
Over-Focus of Near Objects
As explained earlier, Accommodation is the process of moving a distance point of focus to a near point of focus by increasing the convexity of the lens.
Conversely, Spasm of Accommodation, or Pseudo-Myopia, is a condition that occurs when the convexity achieved for the near point of focus “locks in” and won’t release again to view distant objects clearly.
The resulting blur of Pseudo-Myopia is not a consequence of continued development of the visual system, or myopia progression. It is due to an over-focus of near objects, often seen in college students or people who work exclusively in front of computer screens. Unfortunately, this condition is often misdiagnosed, resulting in an unnecessary eyeglass prescription and inadvertent worsening of distance vision.
An Example of “Locking In”
An example of Spasm of Accommodation, or “locking in” is often seen in college students.
Many patients in their late 20’s and early 30’s report having perfect vision until sometime during or immediately after their college years. The first change they report is a blur of distance objects after reading, studying or hours of computer work - and having to blink or squint to see far away again. The person is looking at a distant object, but their eye hasn’t let go of the focus from the book or computer screen. The person is unable to relax Accommodation. Vision for distant objects gradually returns, but slower and slower until the distance vision is permanently blurry.
With this in mind, they make an eye appointment where their main complaint to their eye doctor is distance blur. Because of this, they are prescribed eyeglasses for distance. The good news is that they do see better. The bad is they become dependent on the glasses, and the problem due to the near focus and “locking in” was never addressed.
However, if it was clear that the problem was the change in focus from distance to near, they may have been prescribed reading glasses to help them focus at near and solved the problem. This could have halted the need for full-time glasses for distance, and the resulting dependence on the distance prescription. Distance glasses clear blur, but the problem of near over-focus remains and the cycle of annual prescription changes and increases continues. If the near point vision problem is not addressed, the progression of pseudo-myopia will eventually lead to more dependence on the distance prescription.
Lack of Peripheral Vision
The latest research on myopia is showing that depriving someone of peripheral vision might be another cause of an increase in myopic prescriptions in adulthood.
When we look out at a distance, we use our central and peripheral vision. When we look close to read or do computer work, we use less of our peripheral vision. Lack of stimulation of the periphery over long periods of time can lead to a distance prescription that is geared towards correcting myopia.
In order to minimize the effect, one should increase their reading distance or computer working distance.
What Can Be Done?
As a Patient
For the reasons stated above, it is increasingly important to explain your vision problems in detail to your eye care professional.
Communicating how your vision symptoms began, when they crop up or worsen, all work-related or environmental conditions that may affect your vision, previous eye or health conditions and medications in your eye exam are important for your eye care professional to properly diagnose your vision problems and to prescribe the proper treatment.
As an Eye Care Professional
Similarly, your optometrist or eye care professional should ask you all the above questions in order to effectively and properly diagnose your vision problem. However, diagnosis does not work in a vacuum and all eye care practitioners are not created equal. At Shady Grove Eye and Vision Care, we take the time with every patient to ask the right questions in order to facilitate the proper care and treatment options.