Strabismus affects much more than the alignment of the eyes. Vision is a complex process that involves 2/3 of the connections in the brain to produce vision, make sense of visual information (visual perception) and integrate vision with the other senses. Strabismus affects several aspects of vision, including:
AMBLYOPIA (Lazy eye)
Strabismic amblyopia is caused by certain types of strabismus, or eye turn. With strabismus, one eye turns in, out, up or down. When the eye is turned relative to the other it interferes with normal binocular vision functioning. As a result of this eye misalignment amblyopia develops in one eye. Along with reduced vision, the brain also develops suppression, a process by which the visual input from one eye is ignored by the brain. Suppression cannot be treated with glasses, contacts, or LASIK and instead one must restore binocular vision functioning through an active process.
BINOCULAR VISION (Eye teaming)
The ability to use the two eyes together is a crucial visual skill. Difficulty with eye teaming results in a number of symptoms, including: double vision, headaches, eyestrain, difficulties with reading fluency, skipping or re-reading lines of text, words moving on the page, difficulty concentrating during visual tasks and fatigue. Optimum binocular vision functioning is important for both academic and athletic success.
OCULOMOTOR FUNCTION (Eye tracking)
When a strabismus is present it creates a situation where both eyes do not work efficiently. Binocular vision dysfunction makes eye tracking more difficult, especially when the individual alternates between fixating with two eyes, the right eye and the left eye. The constant changing of binocular vision status results in a constantly changing visual input, meaning the brain receives inconsistent information about the direction and speed of a moving object.
CONTRAST SENSITIVITY (Ability to distinguish differing shades of gray)
Contrast sensitivity is an important aspect of vision. Low levels of contrast sensitivity impair mobility. Contrast sensitivity helps one judge the terrain. For someone with poor contrast sensitivity a sloped incline and a set of stairs may look the same, making it difficult to navigate through the world. Conversely, excellent contrast sensitivity helps athletes track moving objects and perform at high levels.
DEPTH PERCEPTION (3D vision)
Depth perception is important for many reasons. For some, the ability to see depth lets them enjoy their favorite movie in 3D. For others, depth perception is important for work or hobbies. Depth perception is important for everything from driving, hitting a baseball, and threading a needle. The importance of depth perception is easily realized by covering one of your eyes. It is much more difficult and uncomfortable to move through the world while only using one eye.
SUPPRESSION (Ignoring one eye)
Suppression is a neurological response to stress on the binocular vision system. When strabismus is present, one eye fixates (looks at the target) while the other is turned away from the target. This creates a situation where the brain begins to ignore the visual input from the turned eye. With time the brain begins to rely on the visual input from the fixating eye to eliminate double vision, eyestrain, or other symptoms. Suppression must be properly treated to restore proper binocular vision functioning.
VISUAL-MOTOR INTEGRATION (Eye-hand coordination, gross and fine motor abilities)
When strabismus negatively impacts the aspects of vision just discussed, it also makes motor tasks more difficult. Many motor tasks are driven by the eyes and vision. The eyes tell the body when and how to react. People with strabismus may appear clumsy or have difficulty with athletics. It is possible for someone with strabismus to achieve some success with visual-motor tasks, however it is extremely difficult for them to achieve their full potential.