Case report Neuro-Ophthalmology 0165-8107/02/US$22.00 Neuro-Ophthalmology – 2004, Vol. 28, Nos. 5–6, pp. 221–229 c  2004 Taylor & Francis Ltd. DOI: 10.1080/01658100490889650 Accepted 12 March 2004 Effects of visual fixation and convergence on periodic alternating nystagmus due to MS Siobhan Garbutt 1,3 Nimish Thakore 2 Janet Rucker 1 Yanning Han 1 Arun N. Kumar 1 R.J. Leigh 1 1 Departments of Neurology and Biomedical Engineering, Veterans Affairs Medical Center, University Hospitals, and 2 Metrohealth Medical Center, Case Western Reserve University, Cleveland, OH, USA, and 3 Department of Ophthalmology, Great Ormond Street Hospital for Children NHS Trust, and Department of Visual Science, Institute of Child Health, London, UK Correspondence and reprint requests to: R. John Leigh, M.D. Department of Neurology University Hospitals 11100 Euclid Avenue Cleveland, OH 44106-5040 USA Tel: (216)-421-3040 Fax: (216)-231-3461 E-mail: rjl4@po.cwru.edu Acknowledgements: Supported by NIH grant EY06717, Office of Research and Development, Medical Research Service, Department of Veterans Affairs and the Evenor Armington Fund (to Dr. Leigh). We are grateful for suggestions during discussion with Drs. U. B¨ uttner, B.Cohen, D. Riley, J. Sharpe, and D. Zee. Abstract We studied a young woman with multiple sclerosis, who de- veloped periodic alternating nystagmus (PAN) with a period of oscilla- tion of about three minutes. Neither visual fixation of a stationary target nor large-field optokinetic stimulation substantially influenced the cycle of PAN. During convergence, induced by fixation of a near target, PAN was suppressed by over 70%. Treatment with baclofen abolished her nys- tagmus, but optokinetic and pursuit responses remained impaired. Con- vergence during viewing a near target did not increase the response (gain) of her vestibulo-ocular reflex. We postulate that visual drives were able to suppress PAN independently of any effects on vestibular responses and were prevented from exerting effects on velocity storage and vestibular gain adjustment by demyelinating lesions affecting her pontine nuclei and cerebellar circuits. Key words Optokinetic nystagmus; baclofen; cerebellum; multiple sclerosis; vergence Introduction Periodic alternating nystagmus (PAN) is a spontaneous horizontal nystagmus, present in primary gaze, that reverses direction approximately every two minutes. Although PAN was once viewed as a clinical curiosity, it is now as well understood as any form of ac- quired nystagmus. 1 An early insight by Kornh ¨ uber 2 was that PAN was related to a naturally occurring phenomenon—the reversal phase of Periodic alternating nystagmus 221