Can motion parallax provide depth information for low-vision observers?

Purpose. Many people with low, vision do not have binocular depth peieeption (steieopsis) and it is not known what depth cues they use. Motum parallax is a monocular depth cue that can prm ide a vivid and reliable depth percept. We asked whether people with different forms of low vision could use motion parallax to improve depth judgements, and how the improvement compared with that of normal subjects. Methods. Subjects monocularly viewed 3 vertical cylinders and indicated which one was at a diffeient depth than the other two. For motion paiallax trials. observers moved their heads (in a viewing assembly on rollers) from side-to-side over a range of 6-12cm. For static trials, the viewing assemblu was fixed in place. A suicase procedure was used to find the depth difference coiiespondint: to 50 cone detection. Threshold measurements were collected from 10 low vision subjects will a wide range of acuity (-0.02 to 1.68 logMAR). contrast sensitivity (Pelli-Robson 0.0 to 1.8), and field loss. These data were compared to data from normal-vision subjects with a range of simulated deficits in acuity and contrast sensitivity. Results. For low-vision subjects, depth thresholds with motion paiallax were smaller than those with static viewing by a factor of 2.05 (p<0,01 ). The advantage ol motion parallax was lound across the entire range ol acuity, contiast sensitivity and field loss. Likewise, a factor of 1.95 benefit from motion parallax was found for the normal-vision subjects for all levels of acuitv and contrast. Conclusions. These findings indicate that motion parallax is a robust depth cue across a wide range ot visual deficit. Motion parallax can provide useful depth information for people with low vision.