Hemianopsia - Vision Loss After A Stroke Or Brain Injury

Almost 800,000 people suffer a stroke every year, and it is the most common dis­ability among American adults.' A stroke occurs when there is an interruption of the blood flow to an area of the brain.

There are two types of strokes: an isch­emic stroke, occurring when a blood clot blocks a blood vessel, and a hemorrhagic stroke, occurring when a blood vessel in the brain ruptures and causes dam­age. Some strokes are preceded by brief episodes of stroke symptoms known as transient ischemic attacks (TIA), which are temporary interruptions of blood supply to the brain. Because a TIA can occur hours, days, or weeks before a full stroke, it behooves us to be aware of the symptoms and signs—temporary episodes of weakness, numbness, paralysis of the face, arm or leg (especially on one side of the body), difficulty speaking or understanding simple statements, and loss of balance or coordination.' These symptoms can occur on only one side of the body. To that list should be added any re­port of momentary diplopia, transient loss of visual field, or a passing episode of blurry vision.

Every primary-care optometrist can—and should—as a minimum perform the following work-up on a patient present­ing with any signs:-    History of stroke-related signs and symptoms Best-corrected visual acuity-    Pupil reflexes Cover test, phorias, ocular range of motion-    Threshold visual field testing-    Dilated fundus examination-    Stethoscope auscultation of the ca­rotid arteries for bruitsWhether a clinical ocular deficit is discovered, any transient visual episode should trigger a call to the patient's inter­nist or cardiologist to urge the physician to schedule the patient for a physical. In addition, I proactively write the patient an Rx for carotid Doppler testing and/or a CT scan—this starts the ball rolling. When a patient presents with a known, previously documented stroke, pay at­tention to current complaints of persist­ing hemianopsia, diplopia, or eyelid dys­function. These conditions can often be treated by the primary-care optometrist.

Consider using alternate patching or prism for diplopia. For hemianopsia, prescribe separate pairs of glasses for both distance and near for or consider Side Vision Awareness Glasses designed by the author. Lid massage may help lid paresis.

Because adaptation by a head turn or suppression has not yet occurred. Diplopia also causes symptoms of dizziness, poor balance, trouble read­ing, psychological stress, asthenopia, and headaches. Patients with double vision may mention those complaints but not say "double vision" unless asked.

Most stroke survivors with a known cerebrovascular accident (CVA)-related diplopia have been instructed to patch the deviating eye. This makes the patient happy because the patch resolves the dip­lopia. Unfortunately, patching the deviat­ing eye for too many weeks can embed the binocular dysfunction, reducing the possibility of gaining binocular vision.

Therefore, as a minimum, ensure that the eye patch is alternated daily from the right eye to left eye. To keep the schedule simple, I tell patients to patch the right eye on even-numbered calendar days and to patch the left eye on odd-numbered calendar days.

Keep in mind that when patching to compensate for diplopia, the patient may be annoyed or uncomfortable because of the reduced peripheral vision caused by the patch. In those cases, selective oc­clusion can be used by cutting a piece of Transport surgical tape into a small

rectangle to block central vision in front of the pupil of the deviating eye. The tape blocks double vision and allows the pa­tient to retain an awareness of periphery in the occluded eye, which feels more comfortable and is safer than a tradi­tional eye patch.

Some patients with obvious large an­gles of paretic strabismus do not complain of diplopia. That is because the angle of strabismus is so large that the patient can concentrate on the image straight ahead of the non-strabismic eye while ignor­ing (but not necessarily suppressing) the diplopic image located way off center. Although patients may not complain of diplopia, they may still have behavioral symptoms of confusion, poor balance, or poor ambulation due to visual con­fusion induced by the ambient diplopic image. This problem requires consulta­tion with an OD skilled in treating bin­ ocular vision dysfunction.

Stroke-related binocular dysfunctions with mild-to-moderate paretic angles of strabismus often are capable of gaining a wider range of motion of the effected eye. This can be achieved by having the patient monocularly track a moving tar­get (pursuits) in the direction of the re­strictions several times per day for a few weeks.

Many patients are told by non-optometric doctors that double vision may resolve on its own within a vague timeline of months without mentioning vision ther­apy or prism. It is dismaying that people with stroke-related hemiplegia are rec­ommended to have physical and occupa­tional therapy, but patients with diplopia are given only an eye patch and not af­forded a chance for binocular rehabilitation. I suggest prescribing prism glasses as a stopgap measure to help the patient feel more comfortable.

Simple vision therapy procedures using a Brock string or red-green tranaglyphs may help until vision therapy is initi­ated. Never prescribe a ground prism into glasses until a two- to three-month trial with a Fresnel prism has shown the angle of deviation to be steady and that the double vision has been resolved.

It is important to prescribe the total amount of Fresnel prism with the pris­matic compensation broken up between the two eyes to allow the Fresnel-induced reduction in contrast to be distributed evenly between both eyes.

For example, if an esotropia-related diplopia is resolved with 20 D base-out prism, it may seem simple to prescribe a single 20 D base-out Fresnel prism before the deviating eye. However, the patient will usually complain of blur in the eye with the Fresnel prism. Two 10 D base-out prisms are a better choice because they equalize the 20 D Fresnel-induced poor contrast, which reduces patient complaints.

Furthermore, splitting the prism power between two eyes allows the freedom to fine tune the prism power when, or if, the patient's angle of deviation changes. Peel off one of the Fresnel prisms and replace it with another power as clinically in­dicated. Keep in mind that the angle of the paresis measured when viewing at distance may be very different than at near, so separate prismatic distance glasses and reading glasses are often required.

When prescribing compensating prism for vertical diplopias, remember that the angle of deviation usually varies depend­ing on head position. Be sure to prescribe the vertical prism with the patient's head in a straight-ahead position and warn the patient that a chin-up or chin-down head position will likely cause him to see double in spite of the prism.

A patient whose diplopia is resolved with prism may begin to complain again of diplopia in a few months. Never as­sume that a renewed complaint of diplo­pia implies a worsening of the condition. It may mean that the strabismic angle is decreasing.

Do not be disheartened if a rare patient can't fuse binocularly with any amount of prism. A prism bar may seem to neu­tralize the diplopia while the patient is in the chair, but you may find that when you prescribe Fresnel prisms, the patient still complains of double vision. At times despite re-measuring, fine tuning, and changing prism power, the patient con­tinues to not fuse the diplopic images.

Some neuro-related diplopias are diffi­cult to resolve because of damage in the brain pathways responsible for the binoc­ular vision reflex, and horror fusionalis, when it occurs, is difficult or impossible