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(Investigative Ophthalmology and Visual Science. 2000;41:3798-3804.)
© 2000 by The Association for Research in Vision and Ophthalmology, Inc.

Visual Control of Postural Orientation and Equilibrium in Congenital Nystagmus

Michel Guerraz1, Josephine Shallo–Hoffmann2, Kielan Yarrow1, Kai V. Thilo1, Adolfo M. Bronstein1 and Michael A. Gresty1

1 From the Medical Research Council Human Movement and Balance Unit, National Hospital for Neurology and Neurosurgery, London, United Kingdom; and 2 College of Optometry, Nova Southeastern University, Fort Lauderdale, Florida.

PURPOSE. To investigate how humans with congenital nystagmus (CN) use visual information to stabilize and orient their bodies in space.

METHODS. Center of foot pressure (COP) and head displacements in the lateral plane were recorded using a sway platform and Schottky barrier photodetector, respectively. In experiment 1, a comparison was made of the oscillatory characteristics of body sway with eyes open compared with eyes closed. Experiment 2 studied the postural readjustments made in response to absolute or relative motion (motion parallax) of objects in the visual scene, generated by lateral displacement of background scenery.

RESULTS. Experiment 1 revealed that subjects with CN were not able to use visual information to stabilize COP but were able to stabilize the head at frequencies lower than 1 Hz. Experiment 2 showed that in response to the displacement of a visual display, for both absolute motion and motion parallax, subjects with CN reoriented their body in space in a manner similar to control subjects.

CONCLUSIONS. The results suggest that despite involuntary eye movements, subjects with CN use orientation cues to control their posture, but not dynamic cues useful to control the rapid oscillations that are particularly important at the level of COP. These findings suggest that in CN, visual control of posture is restricted by low-frequency sampling of the visual scene.






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