The influence of visual field position induced by a retinal prosthesis simulator on mobility.

PURPOSE

Our aim is to develop a new generation of suprachoroidal-transretinal stimulation (STS) retinal prosthesis using a dual-stimulating electrode array to enlarge the visual field. In the present study, we aimed to examine how position and size of the visual field-created by a retinal prosthesis simulator-influenced mobility.

METHODS

Twelve healthy subjects wore retinal prosthesis simulators. Images captured by a web camera attached to a head-mounted display (HMD) were processed by a computer and displayed on the HMD. Three types of artificial visual fields-designed to imitate phosphenes-obtained by a single (5 × 5 electrodes; visual angle, 15°) or dual (5 × 5 electrodes ×2; visual angle, 30°) electrode array were created. Visual field (VF)1 is an inferior visual field, which corresponds to a dual-electrode array implanted in the superior hemisphere. VF2 is a superior visual field, which corresponds to a single-electrode array implanted in the inferior hemisphere. VF3 is a superior visual field, which corresponds to a dual-electrode array implanted in the inferior hemisphere. In each type of artificial visual field, a natural circular visual field (visual angle, 5°) which imitated the vision of patients with advanced retinitis pigmentosa existed at the center. Subjects were instructed to walk along a black carpet (6 m long × 2.2 m wide) without stepping on attached white circular obstacles. Each obstacle was 20 cm in diameter, and obstacles were installed at 40-cm intervals. We measured the number of footsteps on the obstacles, the time taken to complete the obstacle course, and the extent of head movement to scan the area (head-scanning). We then compared the results recorded from these 3 types of artificial visual field.

RESULTS

The number of footsteps on obstacles was lowest in VF3 (One-way ANOVA; P = 0.028, Fisher's LSD; VF 1 versus 3 P = 0.039, 2 versus 3 P = 0.012). No significant difference was observed for the time to complete the obstacle course or the extent of head movement between the 3 visual fields.

CONCLUSION

The superior and wide visual field (VF3) obtained by the retinal prosthesis simulator resulted in better mobility performance than the other visual fields.