Latent nystagmus: Release and suppression at will

Purpose. The authors report the cases two unusual patients with infantile convergent strabismus and latent nystagmus. Methods. Electronystagmography was used. Results. The two patients were able to release and suppress their nystagmus at will. With voluntary effort, the nystagmus became as strong as it was when brought out by occlusion of the squinting eye and, in one of the patients, even stronger. The nystagmus beat toward the fixing eye, and the slow phases had slightly decreasing velocity or were linear. Both patients were able to evoke and to stop the nystagmus in front of visual contours and, one of them, also in the dark. Conclusions. This phenomenon could be the result of voluntary control of the visual input contributed by the amblyopic eye and/or a direct influence of will on the slow eye movement and fixation systems. A mechanism related to vergence eye movements is less likely. The ability to release and suppress a latent nystagmus at will is unusual and, to the authors' knowledge, has not been described before.