Amblyopia affects much more than the ability to see 20/20. 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. Amblyopia affects several aspects of vision, including:
VISUAL ACUITY (Clarity of vision)
Individuals with amblyopia experience blurry vision in one or both eyes. When present in one eye, a child may adopt an abnormal head posture (tilt or turn) to compensate for the vision in one eye. When present in both eyes, a child may sit closer to the television or hold a book closer than expected when reading. Children with blurry vision rarely complain because their level of visual functioning is 'normal' for them. Children with one blurry eye complain even less often because they are able to use their better-seeing eye to perform daily tasks.
ACCOMMODATION (Eye focusing)
Accommodation is often reduced in individuals with amblyopia, meaning that they have a difficult time making things clear or keeping them clear. This makes many aspects of classroom learning more difficult. 80% of learning occurs through vision, and when a child has a vision condition it can negatively impact learning. Difficulties with eye focusing can make copying notes from the board, reading and other near activities more difficult. While a child may be able to read an eye chart from across the room during a vision screening, they may find it extremely difficult to see clearly when trying to read and learn.
BINOCULAR VISION (Eye teaming)
Amblyopia is not only one eye seeing blurry but is also a form of binocular vision dysfunction, meaning the eyes have difficulty working together in a coordinated manner. 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.
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 amblyopia is present, one eye may see much better than the other. This creates a situation where the brain begins to ignore the visual input from the lesser-seeing eye. With time the brain begins to rely on the visual input from the better-seeing 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 motor and fine motor abilities)
When amblyopia 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 amblyopia may appear clumsy or have difficulty with athletics. It is possible for someone with amblyopia to achieve some success with visual-motor tasks, however it is extremely difficult for them to achieve their full potential.
VISUAL-AUDITORY ABILITIES (Ability to connect visual and auditory information)
If a child with amblyopia sees someone mouth a word, what they hear can actually be different from what was said. When a child is learning they are required to match visual materials (pictures, words, etc) with auditory materials (the sound of the word, etc). A pilot study recently published in the Journal of the American Medical Association - Ophthalmology indicated that children who have amblyopia may also have impaired visual-auditory speech perception.