A 31-year-old Japanese male with unilateral bouts of transient visual loss lasting for variable periods of time has been observed. In spite of the prolonged duration of some of these attacks (the longest attack lasted 7 1/2 hours), the patient sustained a relatively small amount of functional damage to the retina. Although the exact mechanism underlying these bouts of transient visual loss remains unknown, a discussion of the possible causes of such episodes, as well as the reasons for the relative preservation of vision in spite of the length of these attacks, is included.