Abstract
Purpose :
Retinal prostheses are currently constrained by the number of implantable electrodes. To overcome this hardware limitation, we propose a complementary, software-based design where we spatio-temporally modify images streaming in from the video camera before they are transferred to the implanted electrodes. We hypothesize that specific patterns of image movement will improve visual acuity. Here, we explore the effects of image movement on the acuity of normally-sighted adults. Results from these experiments will be used to rationally design video-modulation algorithms to enhance vision in patients with implanted retinal prostheses.
Methods :
On each trial, subjects were presented with a Landolt C for 330 ms and asked to report whether it was right- or left-facing. Randomly interleaved trials featured three types of image movement: jitter, continuous, and no movement (static). Eye position was monitored to ensure central fixation. In Experiment 1 (n = 8 subjects), the C was centered on the screen with 5° or 7.5° radius and 0.25° thickness. Imposed movements were rotational to hold retinal eccentricity constant across all conditions. In Experiment 2 (n = 19), the Landolt C underwent translation instead of rotation; again, continuous, jitter, and static conditions were interleaved. The C (radius = 0.5° and thickness = 0.25°) was presented in eccentricity bands of 3° ± 1°, 5° ± 1°, or 7° ± 1°.
Results :
In Experiment 1, visual acuity, quantified using d’, was significantly improved by continuous motion (mean ± SEM: 4.54 ± 0.33) but not jitter (1.84 ± 0.18) relative to the static condition (2.03 ± 0.23). In Experiment 2, we observed the opposite effect where acuity was significantly improved by jitter (1.46 ± 0.10) but not continuous motion (0.97 ± 0.09) relative to the static (1.12 ± 0.10) condition. Table 1 lists the results from repeated-measures ANOVA tests and post-hoc comparisons with Bonferroni corrections.
Conclusions :
Our initial results support the hypothesis that image movement improves visual acuity, allowing us to develop algorithms that improve the functioning of implanted prostheses (e.g. Argus II). Ongoing work seeks to elucidate the mechanisms (e.g. attention) that may explain the opposite results in Experiments 1 and 2 to further refine motion algorithms for acuity improvement.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.