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Optokinetic nystagmus in patients with central scotomas in age related macular degeneration
C Valmaggia1, J Charlier, I Gottlob
1Department of Ophthalmology, Kantonsspital, CH-9007 St Gallen, Switzerland. valmaggia@freesurf.ch
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 degrees--10 degrees, 11 degrees--20 degrees, and 21 degrees--30 degrees. OKN was elicited with black and white stripes moving nasally to temporally or temporally to nasally on a screen subtending 54 degrees x 41 degrees at four velocities (15, 30, 45, and 60 degrees /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 degrees--10 degrees and 11 degrees--20 degrees. A significant difference in OKN gain was found between the group with scotomas of 21 degrees--30 degrees and all other groups at stimulus velocities of 30, 45, and 60 degrees/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.
