|
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
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.
Vertical Imbalance
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
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 is 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.
Accommodative (Focusing) Problems
To change our focus from distance viewing to near for reading, our brain must interpret how far away the object in space is located and then send a signal to the ciliary
muscle inside our eye causing it to change the shape of the crystalline lens to exactly focus for that distance.
Our focusing ability is greatest in childhood and progressively declines throughout most of our life until after age forty, the focus has declined to require reading lenses
or bifocals. Trauma to the brain may reduce the ability to focus accurately in young people and may lead to the need for reading correction or bifocals. Spasms of accommodation
may occur causing over focusing and may present as a temporary increase in myopia.
Post Trauma Vision Syndrome may impair our ability to interpret spatial relationships and accurately coordinate the focus and convergence mechanism.
|