Vision plays a significant role in balance. Approximately twenty percent of the nerve fibers from the eyes interact with the vestibular system. There are a variety of visual dysfunctions that can cause, or associate with dizziness and balance problems. Sometimes these are purely visual problems, and sometimes they are caused from other disorders such as stroke, head injury, vestibular dysfunction, deconditioning, and decompensation.
Visual Dysfunctions Causing Dizziness and Balance Problems
Aneisokonia is a condition where an excessive difference in prescription between the eyes causes a significant difference in magnification of images seen between the eyes. When this magnification difference becomes excessive the effect can cause disorientation, eyestrain, headache, and dizziness and balance disorders. Treatment is with contact lenses, or special magnification size matched lenses called isokonic lenses.
Normally the eyes work in perfect synchrony. However, following trauma, fever, stroke, deconditioning, or sometimes for no apparent reason, one eye will aim higher than the other will. When mild and not enough to cause double vision this is called hyperphoria. If excessive to the point of causing double vision, it is termed hypertropia. In an effort to adjust to the vertical misalignment of the eyes, the person will frequently tip their head to mechanically help align the eyes. This in turn can cause disorders in the fluid of the inner ear and resultant dizziness and balance disorders. Treatment is with therapy to correct the muscle imbalance and prisms.
Binocular Vision Dysfunction
Binocular vision refers to how the eyes work together as a team. It is the coordination of convergence and divergence (eye teaming and alignment) with accommodation (focusing). Following trauma, fever, stroke, deconditioning, or sometimes for no apparent reason dysfunctions can occur causing the eyes to be weak or overactive. When this occurs, the eyes will manifest a tendency to drift outwards or inwards. This in turn can cause eyestrain, double vision, muscle spasm and excessive peripheral visual stimulation, which in turn can trigger dizziness and balance problems. Treatment is with lenses, prisms and therapy.
Double vision is among the most disorienting and devastating vision disorders. People suffering from double vision will often times go to great lengths to alleviate the double image because it is so bothersome. Many will actually even patch, or cover an eye, thereby eliminating the vision from one eye just to get rid of their double vision. Double vision is caused when the two eyes do not align, or work together and one eye actually turns out, in, up, or down compared to the fellow eye. The overall encompassing term for this is strabismus. The disorientation from double vision will frequently trigger dizziness and balance problems. Treatment is with lenses, prisms, therapy, partial selective occlusion and rarely surgery.
Ambient Visual Disorder
The ambient visual process frequently becomes dysfunctional after a neurological event such as a Traumatic Brain Injury (TBI) or Cerebral Vascular Accident (CVA). Persons can often have visual symptoms that are related to dysfunction between one of two visual processes: ambient process and focal process. These two systems are responsible for the ability to organize oneself in space for balance and movement, as well as to focalize on detail such as looking at a traffic light. Distortions of the spatial system may cause an individual to misperceive their position in the environment. This in turn can cause dizziness and balance problems with the person showing a tendency to lean to one side, forward and/or backward. Treatment is with specially designed prisms and partial selective occlusion. These techniques work effectively in conjunction with physical and occupational therapy attempting to rehabilitate weight bearing for ambulation.
Eye Movement Disorders
Eye movement disorders typically show up as instability of visual gaze (nystagmus), jerkiness of pursuits (eye tracking), or jerkiness of saccades (visual scanning). Eye movement disorders may be congenital, or acquired. When acquired, some of the typical causes are brain injury, stroke, vestibular dysfunction, multiple sclerosis, and other neurological disease or disorder.
When there is an acute adult onset of nystagmus the brain does not register that it is the eyes that are shaking. Rather, the brain interprets that it is the world and objects in it that are moving. This is called oscillopsia and will frequently cause dizziness and balance problems.
As always, treatment is first aimed at correcting (if possible) the underlying cause for the nystagmus, or other eye movement disorder. Concurrently, the following neuro-optometric rehabilitation approaches may be helpful.
If there is diplopia, prism, and/or partial selective occlusion is indicated. Visual exercises may also help expand the range of single binocular vision. Head position and direction of gaze may help compensate for the oscillopsia by finding a null point where the nystagmus is decreased. Partial selective occlusion can be helpful where (typically) the nasal or temporal aspect of the lenses in eyeglasses are partially occluded with tape. A centimeter or less is usually sufficient. Nasal occlusion helps improve peripheral ambient vision, and temporal occlusion helps block peripheral stimulation. Low amounts of base-in prism can also help stabilize peripheral vision and thereby help the oscillopsia.