Page 41 - BOAF Journal 1 2012:2707

Behavioral Optometry
BOAF
Volume1 Number1 2012
diagram of this in their book, “The Neurology of Eye Move- ments”. Vestibular dysfunction is a very large area of discus- sion and includes many differ- ent types of conditions and deficits.
One of the most common types of challenges is regarding a mismatch between visual and vestibular input. The vestibular ocular reflex and the optokinetic reflex work together to minimize blur during head movement. Wong stated that many patients with vestibular dysfunction pre- sent with blur during and after head movement. Clinically two lines difference with head shak- ing from right to the left is pa- thognomic of a mismatch. But clinically just one line can be indicative of a challenge in processing.
Typical vestibular dysfunc- tion for this mismatch is the use of habituation activities. The most common type of treatment is the use of gaze stabilization where the patient looks at a chart and moves their head right and left while trying to maintain a clear picture of what they are looking at. An optome- trist can provide significant in- put regarding how the proce- dure is done and how success- ful it may become.
An example is a patient who may note the blur and cannot clear the image during head movement. Often low plus lenses and/or low base in prism may be helpful. This allows a difference in spatial processing that helps the patient to organ-
ize the two inputs more effi- ciently and accurately. One reason is that the gain of the VOR is increased with lenses and prisms. This is described in Werner and Press book, “Clini- cal Pearls in Refractive Care”. Another consideration is the use of proprioceptive feedback by placing your hands to the sides of the target of regard. This pro- vides proprioceptive support to visual localization and also adds several other components. The hands generally give you a larger field of view (an aware- ness of hands and target), which probably improves fu- sion. The hands may also be helpful by providing feedback about the importance of the relationship of central to periph- eral visual input. The goal would be to use these inputs to support gaze stabilization, and slowly remove the support so one can do the task by itself.
Visual Field Loss and Uni- lateral Spatial Inattention (Visual Neglect)
The patient who presents with visual field considerations can be significantly impacted during the rehabilitation proc- ess. A patient who bumps into something to one side could have a visual field issue, poor mobility, weakness to one side and a number of other causes. The important consideration is to evaluate if one is present and determine what appropriate guidance, lenses, prisms, oc- clusion and visual rehabilitation will be beneficial.
The first step is to deter- mine if the field concern is due to a visual field deficit, unilateral spatial inattention (USI) or a combination of the two. The first indicator is usually related to the location of the lesion. Occipital lesions are generally related to a visual field loss. Frontal, temporal and frontal lobe lesions tend to be USI with a preponderance located on the right side. Other performance tests can be used to further evaluate the patient’s condition and their recovery.
Typically finger counting can be done to determine if a loss exists. Secondarily, if the patient is aware of the left side with single presentation, you should present both sides si- multaneously. If the patient is not able to pick up the left side, they have dual extinction, which is based on the competition of attention. This is a strong indi- cator of USI. Other behavioral tests may also be used. They include draw a clock, line bisec- tion and star cancellation tests.
In general, field loss does not commonly recover. But one may consider the use of the Gottlieb Rekindle or PELI prism system to provide a tool for easier access to the field loss. The Gottlieb system uses a sin- gle spherical prism placed tem- porally to the eye. The Peli sys- tem uses two Fresnel prism strips that are placed above and lateral to the eye. Typically these patients will show an im- provement (decrease) of their visual field loss, but not a com-
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