PURPOSE: A possibly unique individual with infantile nystagmus syndrome presented with incessant oscillopsia but good stereopsis when viewing binocularly; her nystagmus was greatly reduced with left eye occlusion. We have attempted to explain this and to identify an intervention that preserves binocular vision while maximizing perceptual stability. CASE REPORT AND METHODS: Eye movements were recorded and analyzed for duration of foveation (% time when the target was on or near the fovea and the eye was moving at < or = 4 degrees /sec) under different viewing conditions. Changes in foveation were compared with the patient's reports of her perceptual stability. RESULTS: In her right gaze null with her right eye fixating, foveation was 52.9%. This fell to 32.3% for the same eye in primary position and to 0.8% when viewing binocularly in primary position. When viewing binocularly oscillopsia was incessant; when viewing with her right eye vision was stable except in left gaze. Prism correction of her phoria greatly reduced her oscillopsia when viewing binocularly while preserving stereopsis; foveation went up to 33.7%. CONCLUSION: The patient's ability to maintain good foveation only when viewing with her right eye forces her to choose between stereopsis and stable vision. This may result from the rare combination of (1) requiring good foveation for oscillopsia suppression and (2) nystagmus deteriorating under the stress of maintaining binocularity. There may be many other infantile nystagmus syndrome patients who do not develop oscillopsia but may suffer sufficient asthenopia from a phoria to exacerbate their nystagmus.