Image Stabilization in Central Vision Loss: The Horizontal Vestibulo-Ocular Reflex

Abstract

For patients with central vision loss and controls with normal vision, we examined the horizontal vestibulo-ocular reflex (VOR) in complete darkness and in the light when enhanced by vision (VVOR). We expected that the visual-vestibular interaction during VVOR would produce an asymmetry in the gain due to the location of the preferred retinal locus (PRL) of the patients. In the dark, we hypothesized that the VOR would not be affected by the loss of central vision. Nine patients (ages 67 to 92 years) and 17 controls (ages 16 to 81 years) were tested in 10-s active VVOR and VOR procedures at a constant frequency of 0.5 Hz while their eyes and head movements were recorded with a video-based binocular eye tracker. We computed the gain by analyzing the eye and head peak velocities produced during the intervals between saccades. In the light and in darkness, a significant proportion of patients showed larger leftward than rightward peak velocities, consistent with a PRL to the left of the scotoma. No asymmetries were found for the controls. These data support the notion that, after central vision loss, the preferred retinal locus (PRL) in eccentric vision becomes the centre of visual direction, even in the dark.

Effect of Visual Feedback on the Eye Position Stability of Patients with AMD

“…We also found that the eyes of the patients do not return to primary position in the dark which means that the central nervous system maintains the eye rotation that allows for eccentric viewing (i.e., the PRL) even when scotomata cannot impair vision. This effect was also found in the VOR data collected from the same patients [28] and is congruent with data reported by White and Bedell [9] in a study of the oculomotor reference of people with bilateral macular disease who tend to report looking "straight ahead" when using the PRL-in other words, during eccentric viewing-reflecting permanent changes in the oculomotor reference. Consistent with this, we found a small indication that eye position control in the dark is related to the patient's eye position control in the light.…”

“…The data presented here were collected along with those in an already published study of the active horizontal vestibulo-ocular reflex (VOR) of patients with AMD and controls performed at a frequency of 0.5 Hz [28]. The VOR is an image stabilization reflex that minimizes the motion of a target on the retina during head movement by producing compensatory eye movements in the direction opposite to those of the head.…”