A novel, wearable, electronic visual aid to assist those with reduced peripheral vision

Abstract

Purpose: To determine whether visual-tactile sensory substitution utilizing the Low-vision Enhancement Optoelectronic (LEO) Belt prototype is suitable as a new visual aid for those with reduced peripheral vision by assessing mobility performance and user opinions.

Methods: Sighted subjects (n = 20) and subjects with retinitis pigmentosa (RP) (n = 6) were recruited. The LEO Belt was evaluated on two cohorts: normally sighted subjects wearing goggles to artificially reduce peripheral vision to simulate stages of RP progression, and subjects with advanced visual field limitation from RP. Mobility speed and accuracy was assessed using simple mazes, with and without the LEO Belt, to determine its usefulness across disease severities and lighting conditions.

Results: Sighted subjects wearing most narrowed field goggles simulating most advanced RP had increased mobility accuracy (44% mean reduction in errors, p = 0.014) and self-reported confidence (77% mean increase, p = 0.004) when using the LEO Belt. Additionally, use of LEO doubled mobility accuracy for RP subjects with remaining visual fields between 10° and 20°. Further, in dim lighting, confidence scores for this group also doubled. By patient reported outcomes, subjects largely deemed the device comfortable (100%), easy to use (92.3%) and thought it had potential future benefit as a visual aid (96.2%). However, regardless of severity of vision loss or simulated vision loss, all subjects were slower to complete the mazes using the device.

Conclusions: The LEO Belt improves mobility accuracy and therefore confidence in those with severely restricted peripheral vision. The LEO Belt's positive user feedback suggests it has potential to become the next generation of visual aid for visually impaired individuals. Given the novelty of this approach, we expect navigation speeds may improve with experience.

Fig 1. Components of the LEO Belt.

Images of the LEO Belt showing the location of the eight vibration transducers, including two mounted on the ankles, which vibrate at increasing intensity to signify distance to an object between 0.5-2m (1). The 3D camera is belt-mounted with portable battery (1 and 2, profile view). The top centre transducer also contains the vibration on/off button (3a). The belt is formed of an Intel RealSense 3D camera (3b), Intel Compute Stick (3c) and portable battery (3d).

Fig 2. Experimental protocol.

Visual representation demonstrating the three steps of the experimental protocol. Sighted subjects (blue) were allocated goggles (A-C) to reduce their vision before completing the mazes. Visually impaired subjects (red) completed the mazes in both bright and dim light. Half of the sighted subjects (blue semicircle) repeated the mazes with the variants in a different order.

Fig 3. Maze variants.

Diagrammatic and photographic images of the four maze variants used (A to D), showing that each variant contains seven objects and four directional changes.

Fig 4. Analysis of confounding variables.

Repeated maze attempts from sighted subjects revealed that maze variant (A to D) used had no significant effect on time taken to complete each maze, measured in seconds, (p = 0.380) (a) or ADREV error/time scores (p = 0.182) (b). Age of all subjects, in years, was found to not be statistically correlated with change in ADREV error/time score (p = 0.9187) (c).

Fig 5. Time taken to complete mazes.

Time taken to complete the mazes increased when using the LEO Belt compared to without the LEO Belt. This occurred for all subjects regardless of the stage of reduced peripheral vision (p<0.001) (a). Sighted subjects were slower when using the device (grey) whilst wearing goggle A (p = 0.002), goggle B (p = 0.017) and goggle C (p = 0.018) compared to without (white) (b). The mean increase in time taken was greater for visually impaired subjects with unmeasurable VFs compared to measurable VFs (c). Time taken was not significantly correlated with number of errors made by sighted subjects (p = 0.694) (d). This was also true when focusing only on those wearing goggle C (p = 0.47) (e).

Fig 6. Change in number of errors and confidence scores when using the LEO Belt.

Results from sighted subjects show significant decrease in number of errors when wearing goggle C (p = 0.014) with the LEO Belt (grey) compared to without it (white) (a). Trends from visually impaired subjects show reduced errors in the group with measureable VFs, but increased errors in those with unmeasurable VFs, when using the LEO Belt (b). Self-reported confidence of sighted subjects increased when using the device when wearing goggle C (p = 0.004) (c). Visually impaired subjects had increased confidence overall, most notably in the group with measureable VFs in dim lighting (d).

Fig 7. ADREV Error/Time results.

Sighted subject results suggest poorer performance when using the device (grey) compared to not (white) whilst wearing goggle A (p = 0.001) and B (p = 0.005) but no change with goggle C (p = 0.944) (a). Visually impaired subjects with measurable VFs performed better with the device on average whilst those with unmeasurable VFs performed worse (b).

Fig 8. Questionnaire feedback.

Questionnaire responses revealed user opinions and suggestions for improvements following using the LEO Belt. Opinions were collected from both sighted (white) and visually impaired (grey) subjects on ease to wear, use and comfort of the device (a). Visually impaired subjects were also asked if they owned the device when they would use it (b). Sighted and visually impaired subjects were both asked their views on the future usefulness of the device to others (c) or themselves (d) respectively. All subjects offered suggestions to improve the LEO Belt, shown in a word cloud (e).