A 27-year-old woman reports having had 3 episodes of transient " darkening" of vision in her right eye. Each episode lasted 3 to 5 minutes without any associated symptoms. Her general health is excellent; her only medication is an oral contraceptive. She has no history of migraine. Her examination, including visual fields, is entirely normal. What evaluation and therapy should be undertaken? Transient monocular vision loss (TMVL) of abrupt onset typically represents a focal retinal, choroidal, or optic nerve functional deficit due to ischemia. Historical clues are important, such as asking your patient what area of the visual field was lost; the duration of the loss; and the pres-ence of any neurological symptoms, such as headache, numbness, or weakness. In your patient, the absence of scintillations and headaches and the fact that the vision loss is monocular makes a diagnosis of migraine less likely. A careful history, asking for associated systemic symptoms, is important, although none are reported by your patient. The differential diagnosis of TMVL in young individuals includes several entities. Vasospasm in the eye is thought to be due to spasm involving the retinal circulation and often affects the same eye every time. These patients have a stereotypical pattern of "patchy darkening" of vision for approximately 1 minute, followed by poor acuity for 1 to 5 minutes, followed by a return to base-line. There are no scintillations and no neurological abnormalities on examination. In my opinion, the best "investigation" is a thorough history and neuro-ophthalmic examination. Vasospasm is a benign condition that rarely leads to any permanent visual damage. I have found that the fre-quency of the TMVL events can sometimes be reduced by the use of calcium channel blockers.