Effects of early glaucoma on vection responses

Abstract

Purpose: Vection is the illusion of self-motion induced in stationary observers by large moving scenes. We have previously shown that patients with mild glaucoma have longer vection latencies but vection duration is the same; i.e., the neural responses involved in cancelling the illusion remain intact. No relationship between visual field sensitivity and vection responses was found. The purpose of this follow-up study was to investigate whether vection responses correlate with estimated loss of retinal ganglion cells (RGC).

Methods: Twenty-one eyes of 14 patients with mild glaucoma and 9 control eyes were exposed to a random-dot pattern at 40cm viewing distance in a dark room. The pattern was projected for 2 minutes on a large screen and rotated clockwise at 45 deg/s to induce a sensation of self-rotation. Vection latency, vection duration, and objective and subjective measures of tilt were recorded. Visual acuity, visual field sensitivity, and optical coherence tomography (OCT) exams were obtained for each eye. Medeiros et al.’s combined index of structure and function (CSFI) was used to estimate the amount of RGC loss. This index incorporates measures from both visual field and OCT tests.

Results: All control eyes but only 62% of eyes with glaucoma responded to vection, and only these were included in the analysis. CSFI for controls (mean 3 ± 5%) was significantly smaller than that for glaucoma group (mean 17 ± 12%). Visual acuity was not different between the two groups. Latency for controls (mean 7 ± 4s) was significantly shorter than for the glaucoma group (mean 27 ± 31s), but vection duration and tilt angles were the same for the two groups. In the glaucoma group, objective measure of the body’s maximum tilt angle during vection correlated with CSFI [r(11) = -.55, p = .026] and with cup-to-disc ratio [r(11) = -.71, p = .006].<br /> Clinical characteristics of eyes with glaucoma that did not respond to vection were not different from those that did, except for acuity (i.e., worse by one line for those who did not respond to vection).

Conclusions: More than one third of eyes with mild glaucoma did not respond to vection. Those that did had a delayed response and the objective measure of the body tilt was associated with the estimated number of RGC loss. These results suggest that vection can detect anomalies in early glaucoma.<br />