This is part 3 of the VT series and will focus on problems that can occur with the accommodative system.
To best understand these disorders it is important to dive in a little deeper into what the accommodation process all entails. You can also review Part 1 and Part 2 of our vision therapy series.
What is Eye Accommodation?
If you’ll recall from the previous discussions, accommodation is a process that occurs in the lens of the eye to allow the eyes to focus at various distances.
In particular, during accommodation the lens expands to focus incoming light from a near object onto the retina to produce a clear image.
Accommodation is a very finely tuned process by the eye, if the lens expands too much (over-accommodates) the target will become blurry. Likewise, if the lens does not expand enough (under-accommodates) the target will be blurry.
The blur drives the accommodative process—when blur is detected by the image processing center of the brain it tells the lens to either accommodate more or less until the image becomes clear.
One of the best ways to picture the accommodative process is by thinking about the lens of the eye being similar to the auto-focus on a camera. If an object is blurry the camera lens will move in and out until the image of focus becomes clear. The eye’s lens does this too!
In some individuals, the accommodative system works perfectly without training. In others, however, the lens struggles with fine-tuning itself to the blur—hence an accommodative disorder.
If the accommodation system of one, or both eyes, is off, it can result in eye strain, fatigue, and overall issues when focusing on an up-close object (reading, writing, computer work, etc.).
It is also important to note that accommodation is lost as we age as the lens becomes less flexible over time. Therefore, accommodative disorders are typically only diagnosed and treated in individuals under the age of 30 with healthy, flexible lenses.
To simplify accommodative disorders, the lens can either be too strong/over-functioning—called accommodative excess—or it can be too weak/under-functioning—called accommodative insufficiency.
Accommodation Excess
In accommodative excess, the lens has a hard time relaxing. It prefers to stay in its contracted, expanded, accommodative state.
Patients with accommodative excess often complain of their eyes “feeling stuck” after doing near tasks.
The individual will see well up close, but after 20 minutes or more of near work, the individual will notice he or she has a hard time seeing far away as they cannot get the accommodative system to relax to look far away again.
Accommodation Insufficiency
In accommodative insufficiency, the lens has a hard time contracting to look at an object at near.
Individuals with accommodative insufficiency will struggle to do near tasks such as reading, writing, typing, etc. and often complain of eye strain, blur, and headaches when attempting to do so.
This is because the lens of the eye is not able to contract enough to bring the near object into focus. This is a similar process to what happens in a process called presbyopia.
Presbyopia is part of the natural aging process and occurs as the lens becomes less flexible over time. It typically is not seen until the mid-to-late 40s and is corrected with reading glasses, not vision therapy.
The difference between accommodative insufficiency and presbyopia is that the lens in presbyopia physically is no longer flexible—physically limiting the amount it can change. In other words, presbyopia occurs when the lens is no longer able to accommodate due to aging changes within the structure of the lens.
Accommodative insufficiency occurs when the lens is still young, healthy, and able to flex (i.e. accommodate), however for whatever reason it does not do so. While accommodative insufficiency can also be corrected with reading glasses, vision therapy is an excellent treatment option to help teach the lens how to properly flex and focus on a near target.
Testing for Accommodation Disorders
Accommodative disorders are diagnosed through a variety of tests as part of a binocular vision evaluation.
Sometimes the easiest and simplest solution is a pair of glasses! The lens cannot differentiate accommodative blur from refractive blur and may be “spazzing out” trying to overcome refractive blur.
If glasses are not correcting the problem, a binocular vision evaluation is the next step.
Your eye doctor will check your amplitude of accommodation—the amount or range of accommodation your lens can handle. You will be asked to focus on a small target as it is brought toward your nose. You will be asked to keep that target clear and to let the doctor know when it begins to blur.
This test will be done on each eye individually and with both eyes open together. It will be done multiple times to see if the amplitude of accommodation changes as your eyes tire.
A person’s expected amplitude of accommodation is based on his or her age. Your doctor will know the ranges for your age group and determine if you fall within those ranges for each eye individually and with both eyes together.
Typically, individuals with accommodative excess will have normal amplitudes of accommodation whereas those with accommodative insufficiency will have reduced amplitudes.
Another test used to check accommodation is called a lens rock. Your doctor will have a flipper bar containing both plus and minus lenses. Minus lenses stimulate accommodation whereas plus lenses relax accommodation.
Your doctor will give you a target to look at and set a timer for 60 seconds. He or she will then place a low powered minus lens in front of your eye and ask you to let them know when the target becomes clear.
Then he or she will place a low powered plus lens in front of your eye and ask you to tell them when the target becomes clear. This process will be repeated as many times as possible during the 60 second time limit. This test is again performed on each eye individually, and then together as a pair.
Your doctor will keep track of the number of times the flipper bar is flipped and compare your number to age-normals. If it is reduced, it could indicate an accommodative disorder.
Individuals with accommodative excess will typically have a difficult time relaxing their accommodation, meaning clearing the target image will be more difficult when looking through the plus lenses.
Individuals with accommodative insufficiency will often have the opposite problem. They have a hard time stimulating their accommodative system and therefore will struggle to clear the target image when looking through the plus lenses.
Once your doctor has determined you have an accommodative problem, he or she will determine if it is a monocular problem (one eye only) or a binocular problem. From there, he or she will discuss further testing and create an appropriate vision therapy program designed specially to help your eyes.
Be sure to check back next week to learn about different vision therapy exercises used to help treat accommodative excess and insufficiency!