Effect of Aging and Visual Impairment on Dynamic Visual Acuity with Telescopic Spectacles During Vertical Motion

Abstract

Telescopic spectacles are frequently prescribed for visually impaired patients, but visual rehabilitation with these costly devices is often unsuccessful. The retinal slip hypothesis suggests that one major cause of rehabilitation failure with telescopic spectacles is the result of patients’ inability to maintain adequate stability of magnified images on the retina during unintended head movements caused by ambulation, tremor, and postural instability. The visual-vestibulo-ocular reflex (VVOR), which normally produces eye movements to compensate for head movements, is overwhelmed when the visual effects of head movements are magnified by head-mounted telescopes, permitting instability of images on the retina.1 It has been demonstrated in normally sighted2 and low vision subjects3 wearing telescopic spectacles that horizontal head motion significantly decreases dynamic visual acuity (DVA), the acuity during relative motion. However, clinical studies suggest that spontaneous vertical head motion is an important determinant of successful rehabilitation with telescopic spectacles.3,4 Although vertical optotype and head motion with telescopic spectacles have been demonstrated to impair the DVA of young, normal subjects through the mechanism of retinal image instability,5 DVA for vertical relative motion has not been similarly studied in elderly or low vision subjects. Impaired VVOR performance in these subjects would be expected to compromise DVA.