Visual rehabilitation, or Neuro-Optometric rehabilitation, can help vision problems as a result of neurological disorders or trauma to the nervous system. The use of special therapeutic lenses and/or vision therapy can effectively treat the visual consequences of brain trauma including: double vision, light sensitivity, visual inattention, loss of peripheral vision, poor visual information processing and difficulties with spatial perception.
Vision is Our Dominant Sense
More than just sight, vision is the process of deriving meaning from what is seen. It is a complex, learned and developed set of functions that involve a multitude of skills. Research estimates that eighty to eighty five percent of our perception, learning, cognition and activities are mediated through vision. The ultimate purpose of the visual process is to arrive at an appropriate motor and/or cognitive response. There is an extremely high incidence, greater than 50%, of visual and visual-cognitive disorders in neurologically impaired patients (traumatic brain injury, cerebral vascular accidents, multiple sclerosis etc.).
The areas of vision affected by brain injury can be broken down into four general categories:
- Visual Acuity
- Visual Field
- Oculomotor Abilities
- Visual perception
Visual Acuity: This refers to clarity of sight. It is commonly measured using the Snellen chart and noted, for example, as 20/20, 20/50, 20/200 etc. Visual acuity can be blurred due to various refractive conditions, for example, myopia (nearsighted), hyperopia (far-sighted), astigmatism (mixed), and presbyopia (age related loss of focusing).
Snellen chart is used to measure visual acuity.
Sometimes the refractive error will undergo a sudden change in prescription after a brain injury. This shift may be in response to other changes in the brain or visual motor systems. In some cases, it is appropriate to change the prescription, while in other cases it is best to wait and address the visual motor difficulties first.
Eye disease and/or injury can also interfere with good visual acuity and medical management is needed. For example, dry eye is a commonly overlooked source of blurred vision in brain injured patients. Brain injured patients commonly have more difficulties with dry eye due to decreased blink rates and poor-quality tear production. When dry eye is appropriately treated, improvement in clarity and comfort are often noted.
Visual Field: This is the complete central and peripheral range, or panorama of vision. Various neurologic conditions, such as stroke, cause characteristic losses of the visual field, for example hemianopsia. The person may, or may not, also demonstrate a visual neglect, which is a perceptual loss of vision or inattention to one side of the visual field. This will often interfere with visual motor integration on the side of the visual field loss.
Oculomotor Abilities
- Fixation– The ability to steadily and accurately gaze at an object of regard. This is most dysfunctional in nystagmus, which is an uncontrollable shaking of the eyes.
- Pursuits– The ability to smoothly and accurately track or follow a moving object.
- Saccades– The ability to quickly and accurately look or scan from one object to another.
- Accommodation– The ability to accurately focus on an object of regard, sustain that focus of the eyes and change focus when looking at different distances.
- Vestibular Ocular Reflex (VOR)- A reflex that helps the brain coordinate vision with vestibular (inner ear) information. Patients with VOR difficulties often have trouble with eye movements, but may also have complaints of dizziness or poor balance.
- Binocular Vision or Eye Teaming– Binocularity is the ability to coordinate both eyes together as if they were a “team”. There are several areas or types of difficulties that relate to eye teaming.
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- Eye Alignment– This also can refer to eye posture. Sometimes there is a visible misalignment of the eyes called a tropia or strabismus. Sometimes this is due to damage to one of the three cranial nerves that controls eye movements. This often causes a limit in the range of motion in the affected eye creating a sudden onset of double vision.
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- Eye Phoria Dysfunctions– Even if the eyes are straight and “align” with each other, they can still have difficulty posturing closer, farther or higher than the target. This is especially true as objects are brought closer or when reading. Eye phoria dysfunctions can cause eye fatigue and strain or double vision.
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- Convergence– The ability to accurately aim the eyes at an object of regard and to track an object as it moves towards and away from the person. Convergence insufficiency is the most common type of eye teaming problem after a brain injury. Eye teaming problems can cause blurry, distorted or double vision, eyestrain, headaches and decreased attention/comprehension, especially when reading.
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- Stereopsis– Stereopsis or depth perception is the ability to integrate information from both eyes to create a single, three dimensional image (3-D vision). Loss of depth perception is commonly related to poor eye alignment and convergence problems.
Visual Perception
- Peripheral/Spatial Awareness– Also sometimes called useable field of view. This is the volume of information the person can be aware of while fixating on something. This is intimately related to oculomotor and visual motor skills.
- Localization– The ability to accurately locate an object in real space. This is related to, but a separate skill than stereo vision or depth perception testing.
- Egocentric Midline Shift- This is a shift in the perception of where “midline” or straight ahead exists. It can be the result of a binocular vision disorder or due to damage to higher levels of the brain that process spatial information.
- Oculocentric Midline Shift– This is a shift in the perception of “midline” or where straight ahead exists in one eye.
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