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Optokinetic nystagmus in patients with central field defects
  1. LUC CREVITS
  1. Department of Neurology, Neuro-Ophthalmology Unit, Ghent University Hospital, De Pintelaan 185, B-9000 Ghent, Belgium
  1. luc.crevits{at}rug.ac.be

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Editor,—We read with interest the article by Valmaggia et al 1 who studied optokinetic nystagmus (OKN) in patients with macular degeneration. They noted abnormalities of OKN gain only in patients with large central scotomas. Therefore, an intact macula seems not to be necessary for the generation of OKN. This implicitly suggests an important role of the peripheral retina in eliciting an OKN. In this context, it is interesting to note that we observed an inversed OKN in some patients with defects of the central visual field.2 An inversed OKN is an OKN with fast phases in the direction opposite to the stimulus. The eyes in which an inversed OKN was provoked more easily or at lower stimulus velocities had the largest central field defects. It was a prerequisite to elicit an inversed OKN that the attention was actively directed to the central field defect itself, but could also be influenced by a remarkable property of the more peripheral retina to induce an OKN in the inversed direction, counteracting the OKN in the classic direction. In this central-peripheral interaction, we proposed an important role for spatial-selective attention.3 It would be very interesting to find a method to monitor direction of attention simultaneously with OKN.

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