LOCOMOTION IN LOW LUMINANCE WITH NON IMMERSIVE HEAD MOUNTED DEVICE FOR PATIENTS WITH NIGHT BLINDNESS

Abstract

Purpose: Retinitis pigmentosa (RP) is characteristically associated with reduced dark adaptation, which may lead to difficulties for locomotion in dim light specially when lighting abruptly decreases. We tested a non immersive Head Mounted Display (HMD) providing a luminance-enhanced video image to determine its value for affected individuals in dim light condition.

Methods: Nine RP patients were enrolled (age from 23 to 81 years, mean 43). All patients complained of altered dark adaptation. We evaluted visual acuity (VA), horizontal binocular visual field (VF) and dark adaptometry (Goldmann-Weekers - GW). We tested a non-immersive HMD (Essilor Int., Institut de la Vision, Paris, France; Lumus, Rehovot, Israel), which provides a processed video image displayed on transparent lenses. Image was a luminance-enhanced view of the surrounding environment. Patients were asked to walk along a straight corridor (white walls and floor, 30 meters long). Five conditions were explored as follows: (1) in a clear corridor in photopic condition (700 lux), and (2) in dim light (5 lux); (3) in a corridor with 6 obstacles (white boxes 30x35x55cm) laid out on the floor in photopic, (4) and dim light. The last condition (5) in a corridor with 6 obstacles, in dim light, was tested using the HMD. The walking speed was measured 3 times in each condition. Spatial disposition of obstacles was modified between consecutive trials. Patients were exposed to photopic lighting during 5 min before each trial to prevent dark adaptation.

Results: Four of nine patients performed better using the HMD than without: between-groups comparison showed that these four patients increased their walking speed when obstacles were laid out in dim light (mean walking speed without HMD = 0.35 m/s; SD = 0.07, mean walking speed with HMD = 0.47 m/s; SD = 0.06) ;( F (4,152) =12.1; p<.01). For these four subjects, alteration in dark adaptation reduction in VA and VF were more pronounced than for the remaining patients.

Conclusions: Significant HMD benefits were observed in patients demonstrating severe handicap in dim light. However, in patients suffering to a lesser degree from night-blindness, the device did not prove to be invaluable.

Keywords: 549 image processing • 753 vision and action • 702 retinitis