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Optokinetic Nystagmus Elicited by Filling-in in Adults with Central Scotoma

¹ From the Department of Ophthalmology, Kantonsspital St. Gallen, Abtwil, Switzerland; and the ² Department of Ophthalmology, University of Leicester, Warwick Medical School, Leicester, United Kingdom.

PURPOSE. Filling-in is the perceptual completion of physiological, pathologic, or artificial scotomas. Three patients are described, in whom optokinetic nystagmus (OKN) was present during filling-in.

METHODS. Three patients with age-related macular degeneration with large central scotomas were included in the study. OKN was elicited with black and white stripes moving nasally to temporally or temporally to nasally at four velocities. OKN gain was measured using infrared oculography.

RESULTS. While looking at the OKN stimuli, the patients either did not see the stimulus (without perceiving a positive scotoma) or filled in the scotoma and perceived the stripes. Simultaneously with filling in the scotoma, OKN eye movements were elicited in all three patients. The filling-in phenomenon was present for all stimulus directions and velocities, appeared within seconds, and was followed immediately by eye movements corresponding to OKN. OKN gains during filling-in were similar to those of age-matched control subjects without scotomas. No asymmetry was noted between temporal to nasal or nasal to temporal stimulation.

CONCLUSIONS. Motion-sensitive areas of the visual cortex may be activated and trigger the generation of OKN, supporting an active process. Alternatively, OKN is suppressed when subjects are not filling-in, while the subjects are fixating the central scotoma or edges of the scotoma. That the subjects did not perceive positive scotomas suggests that an active process is more likely.

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