Transient Monocular Visual Loss
What causes it?
If transient vision loss affects only one eye, ischemia is the principal cause.
But watch out for this trap: patients who suffer hemifield transient visual loss often wrongly attribute it to the eye with the temporal field loss! They do not notice the nasal field loss in the other eye. Yet if they describe a missing half-field or could not read well during the episode, presume transient binocular visual loss.
There are five ways that an eye can become briefly ischemic:
- embolism originating in an or in the heart
- carotid or ophthalmic artery stenosis with a brief dip in blood pressure
- impending occlusion of the circulation to the retina or optic nerve
- optic disc edema which impedes retinal circulation
- vasospasm of retinal arterioles: this is the presumed mechanism when there is no evidence for any other mechanism
What to do?
It depends on the patient's age.
If age 40 years or above, presume a thromboembolic cause, prescribe aspirin, 325 mg/day. Get a prompt ophthalmologic exam, and if unrevealing, get a prompt evaluation for a carotid embolic source or a hypercoagulable state. Endarterectomy may be indicated for high grade cervical carotid stenosis.
If under age 40, presume vasospasm but get a prompt ophthalmologic exam anyway. If it is unrevealing, complete a screening work-up for blood dyscrasias and thromboembolic disease by ordering basic chemistries and carotid ultrasound, but expect the entire evaluation to be negative. If so, no treatment is necessary.