Convergence Nystagmus Associated With Arnold-Chiari Malformation

To the Editor. —In the March 1990 issue of theArchives, Mossman et al 1 detailed the neuro-ophthalmologic findings of a convergence nystagmus associated with Arnold-Chiari malformation type I in a 17-year-old boy. This type of nystagmus, occurring usually with lesions of the pretectal region, 2,3 appeared only during neck movements and Valsalva's maneuver, and was absent in the primary position of gaze with the head in the neutral position. We congratulate the authors for the accuracy of the electro-oculographic and magnetic resonance imaging studies of the case, and we agree with their brilliant hypothesis that, even in the absence of an overt pretectal lesion, the appearance of convergence nystagmus might be explained on the basis of transient dysfunction of periaqueductal structures provoked by mechanical and/or hydrodynamic mechanisms occurring during neck movements and Valsalva's maneuver, ie, distortion of the aqueductal region and transient rise of cerebrospinal fluid pressure within the