Visual stabilization of posture in retinitis pigmentosa and in artificially restricted visual fields

Purpose. To investigate the relationship between retinitis pigmentosa (RP) progression and the visual contribution to posture stabilization; to examine the extent to which visual-field diameter affects the visual contribution to posture stabilization. Methods. Posture information was recorded in 35 subjects with well-characterized RP and in 20 subjects with normal vision. Data were collected as each subject stood in a dark environment and as each subject viewed a stationary visual display. In both conditions, somatosensory feedback was concurrently altered. Data were also collected on 10 additional subjects with normal vision wearing field-restricting goggles (visual-field diameters ranged from 26.5 down to 6°). Results. RP progression is accompanied by a steady decrease of the visual stabilization of posture, from normal values at the onset of the disease to the absence of visual stabilization and, eventually, to visual destabilization of posture. Decreasing visual field diameter in the subject with normal vision resulted in a linear decrease of the visual stabilization of posture. However, subjects with RP with comparable visual-field loss showed significantly lower visual stabilization than normal subjects with artificially restricted fields. Moreover, subjects with normal vision with restricted visual fields as small as 6° failed to show visual destabilization of posture. Conclusions. Most likely, the additional reduction in the visual stabilization of posture shown in subjects with RP, as well as the visual destabilizing effect manifest in the late stages of RP, is caused by anomalous processing of visual information in the remaining visual field.