BACKGROUND Reports on the impact of a loss in the central field of vision on optokinetic nystagmus (OKN) are varied. A study was therefore undertaken to reassess the role of the central retina in the generation of OKN in a large group of patients with age related macular degeneration.
METHODS Four groups of 20 patients were examined: a control group without scotoma and three groups with absolute central scotomas measuring 1°–10°, 11°–20°, and 21°–30°. OKN was elicited with black and white stripes moving nasally to temporally or temporally to nasally on a screen subtending 54° × 41° at four velocities (15, 30, 45, and 60°/s). OKN gain was measured using infrared oculography.
RESULTS There was no significant difference in OKN gain between the control group and those with scotomas of 1°–10° and 11°–20°. A significant difference in OKN gain was found between the group with scotomas of 21°–30° and all other groups at stimulus velocities of 30, 45, and 60°/s (p<0.05). OKN gain significantly diminished with increasing stimulus velocity (p<0.05). No statistically significant difference was found in OKN gain between stimuli moving temporally to nasally and nasally to temporally.
CONCLUSION Abnormalities of OKN gain were noted only in patients with large scotomas. An intact macula is therefore not necessary for the generation of OKN.
- optokinetic nystagmus
- age related macular degeneration
- central scotoma
- visual field defect
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