Abstract

Telescopic spectacles are telescopes mounted in spectacle frames for use as aids for the visually impaired. Although their magnifications ranging typically from 2-8× offer substantial potential visual advantage, these devices are also subject to two significant limitations: first, their field of vision is limited, and second, they magnify the visual effects of head movements. The field limitation creates problems with orientation in the environment, and requires visual search to locate the target of interest for detailed scrutiny. The visual-vestibulo-ocular reflex (VVOR) normally produces eye movements equal in velocity but opposite in direction to head movements in order to stabilize images of fixed objects on the retina. Normal VVOR gain, eye velocity divided by head velocity, is thus ordinarily equal to 1.0. When telescopic spectacles are worn, however, the visual effects of head movements are magnified, so that a VVOR gain equal to telescope magnification is ideally required. For high velocity head movements, the VVOR is overwhelmed and actual gain is less than ideal, permitting instability of images on the retina,¹ and consequent reduction in dynamic visual acuity, the acuity during motion.² However, due to the limited visual field extent, rapid searching head movements would be desirable to minimize search time. What search strategy represents an optimal balance between these two effects? We studied visual search strategies for several types of targets.

© 1993 Optical Society of America