Abstract

Recently there has been increased interest in how the visual system compensates for gaps in perception due to scotomas (e.g., Ramachandran, 1992). However, it has been difficult to control the placement of the stimuli so that the stimuli are always at the desired retinal location relative to the scotoma. Lettvin (as cited in Ramachandran, 1992) reports that vertically misaligned lines across the physiological blind spot are perceived as being in-alignment. But, Lettvin also reported that horizontal misaligned lines are not perceived as being in-alignment. This study measures the horizontal and vertical alignment threshold of lines across a scotoma by using a scanning laser ophthalmoscope to place the lines at specific retinal locations relative to the scotoma. In addition, this study measures the horizontal and vertical bias in the perceived in-alignment lines to determine the amount of distortion in spatial position across a scotoma. This spatial distortion is often referred to as metamorphopsia, a perception in which objects appear distorted and/or larger or smaller than their actual size. The measurement of metamorphopsia using a vernier acuity task was proposed by Enoch et al. (Enoch, Baraldi et al., 1988), although the technique has been developed for subjects with ocular media opacities and not subjects with scotomas (Lakshminarayanan, Aziz et al., 1992). This study will determine whether subjects with macular scotomas can have spatial position perception that includes a distortion in the bias and/or a higher threshold for in-alignment mapping from object space to perception space.

© 1993 Optical Society of America