Focusing, eye teaming, and eye tracking dysfunctions
Accommodative (focusing), Vergence (eye teaming), and Oculomotor (eye tracking) Dysfunctions
Accommodation is the ability of a child or young adult to adjust their focusing system (change focus as you would in a camera) to allow a sharp image to reach the retina (back of the eye). As an object is brought closer to the face, accommodation / focusing has to increase to keep an image clear. This process is controlled by the lens inside of the eye (behind the iris / colored part of the eye). As the lens becomes rounder, accommodation / focusing increases. In children, the amount of focusing power (amplitude), the ability to stay focused on something for a period of time comfortably (sustainability), and the ability to quickly change that focus between different distances (facility) should be high. With age, the lens loses its elasticity resulting in the reduction of both the amplitude (amount of power) and facility (ability to change it quickly) and sustaining close working distances becomes uncomfortable – which is why we need to wear reading glasses when we get older.
Vergence is the simultaneous inward (convergence) or outward (divergence) turning of the eyes allowing both eyes to look at the same place at the same time. If the eyes do not both point at an object at the same time, the object will appear double (see two of something when it should be one). When looking at an object far away, the eyes diverge (turn out) and seem parallel to each other. When an object comes closer, the eyes have to converge (cross) to keep that image single. The accommodative (focusing) and vergence (eye teaming) systems are very closely interlinked. Thus, the amplitude, sustainability, and facility of the vergence system may decrease with age but not always. In children and young adults, the muscles controlling the movement of the eyes are healthy and have enough strength to control the movement of the eyes. The exact problem in vergence dysfunction is not known, but incorrect eye teaming may stem from a miscommunication between the eyes and the brain on where the eyes should be pointing.
Oculomotor dysfunction occurs when the eyes are unable to quickly, smoothly, or accurately move from one object to another. In order to process visual information accurately, the eyes must be able to properly track objects and jump from one object to another. Good oculomotor skills are critical as they are used in reading, writing, math, copying information, finding something/someone in a background, sports, art, and many other aspects of the visual world. Oculomotor dysfunction, like vergence dysfunction, is usually due to faulty development of eye muscle control.
The brain is not able to process information that it gets from the eyes unless it is clear and distinct. The ability to find and track something and keep it clear and single is crucial for proper visual function and learning.
Symptoms commonly associated with accommodative, vergence, and oculomotor dysfunction include
→ blurred vision
→ difficulty reading
→ blurry vision after sustained reading
→ blurry vision at the end of the day
→ ocular discomfort
→ ‘pulling’ sensation around the eyes
→ eye tiredness or fatigue
→ double vision
→ rubbing eyes when reading
→ avoidance of reading
→ sleepiness when reading
→ squinting, rubbing, or closing an eye
→ motion sickness
→ loss of concentration
→ skipping words / lines
→ problems understanding what you read
→ problems remembering what you read
→ problems copying from the board
→ difficulty with math
→ difficulty with sports
→ seeing words move on a page
→ burning or tearing of the eyes
→ poor eye-hand coordination
→ difficulty following a moving target
→ poor judgement in depth
→ decreased efficiency or productivity
→ need to use finger to keep place
An accommodative, vergence, or oculomotor dysfunction can have a negative effect on a child’s school performance, especially after third grade when the child must read smaller print and reading demands increase (changing from learning to read to reading to learn).
Many children do not report any problems because they do not realize that they should not be having these problems. They think that everyone sees and feels this way.
Although these conditions may change with time, they rarely resolve when left untreated.
Glasses, vision therapy, prisms, and sometimes surgery should all be used appropriately to provide the best visual and functional outcome for a child. The goal of optometric vision therapy is to allow a child to perform their daily tasks comfortably under sustained conditions.
A specific therapy regimen is designed to address the underlying condition and relieve any associated ocular, physical, or psychological symptoms. The duration of treatment depends on the particular patient and their combination of symptoms and problems. The child will be seen by an optometrist trained in vision therapy once a week for 40 minutes and homework will be assigned for the rest of the week – vision therapy will be minimally useful if the homework is not performed as assigned. The completed homework should be brought in at the next appointment.
The first stage of therapy will work to equalize the ability of each eye to quickly and accurately perform the required tasks. This will be followed by integrating the two eyes together and then work to make these skills automatic and effortless. Periodic re-evaluations will be performed in the course of therapy to evaluate its progress and effectiveness. Glasses may sometimes need to be worn for reading even after therapy is concluded.