Diplopia from a recent stroke is confusing to the patient 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 survivor with a known cerebrovascular accident (CVA)-related diplopia has 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 Transpore 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 binocular 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.