Abstract
Purpose :
Recipients of electronic visual prostheses such as the Argus II and ICVP are required to control their gaze, to avoid subjective shifts caused by the efferent copy of the eye movement commands. Moreover, eye and hand movement recordings are used in ICVP phosphene mapping procedures. Little is known about fixation stability and saccadic eye movements in people who are blind, so a small study was conducted to examine this.
Methods :
Subjects with acquired blindness or ultra-low vision and control subjects were seated in front of a 36” diameter concave spherical cap, wearing a VIVE Pro Eye Headset to record their eye movements, and two Polhemus G4 trackers on both index fingers. The index fingers were placed on designated locations (center or 25° left and right) on the cap labeled with tactile dots. Subjects were instructed to perform three timed tasks using their (unseen) fingers as proprioceptive references: fixation, saccade and smooth pursuit. Each task was repeated three times. Data analysis was performed by comparing the dispersion of gaze during fixation, and the speed of saccades
Results :
Across all obtained fixation data in 5 blind subjects, the average dispersions of gaze at the center, 25° right and 25° left are, respectively, 1.03(±0.19)°, 1.42(±0.34)° and 1.30(±0.23)°, significantly larger than those of 4(?) normally sighted subjects, 0.55(±0.16)°, 0.71(±0.21)° and 0.85 (±0.20)°. Across all obtained saccade data, the average saccade speed in the blind is 70.00 (±4.86)°/s, significantly slower than that of the normally sighted: 209.90(±9.28) °/s. Blind subjects on average completed 3 accurate saccades with slightly smaller amplitudes than 25° per trial, while normal subjects completed 10, but with a tendency to exceed 25°. All obtained smooth pursuit data showed variable results, and will be analyzed further.
Conclusions :
As anticipated, the larger gaze dispersion in fixation and slower saccade speed indicate impaired oculomotor control following adventitious vision loss. Nonetheless, these blind individuals are capable of holding fixation and making targeted saccades. Further studies will examine possible effects of duration and time course of preceding vision loss on the decrease in eye movement control.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.