Impact of Visual Motion Displayed in a Non-Immersive Head-Mounted Device on the Balance of Patients with Age-Related Macular Degeneration

Abstract

Purpose: Age-related Macular Degeneration (AMD) results in a reduced visual acuity (VA). Head-Mounted Displays (HMD) may be useful for affected individuals, by magnifying, freezing and dragging the view, vertically or horizontally, to relieve from reduced field of vision due to magnification. However, changes in image (size and movements) are susceptible to disturb visuomotor coordination and thus to disrupt postural control. The aim of this study was to evaluate the impact of changes in image on the balance of AMD patients, when using a non-immersive HMD.

Methods: Three groups were included: 12 patients with atrophic AMD (AMDs: age between 62 and 81 years, mean 70; VA between +1.22 and +0.28 logMAR , mean +0.62), 6 older healthy subjects (OH: age between 65 and 75 years, mean 70; VA between 0 and -0.2 logMAR, mean -0.04), and 5 young healthy subjects (YH: age between 30 and 48 years, mean 37 ; VA between +0 and -0.1 logMAR, mean -0,01). Subjects stood in the dark on a stable force plate. A virtual street was projected onto a wall-screen. For comparison, subjects were tested without HMD eyes closed (EC) and eyes open (EO). When tested with HMD, subjects wore a non-immersive binocular opto-electronic device, displaying an image through transparent lenses. They viewed the scene moving successively in vertical and horizontal directions and from one size to another. In non-immersive mode, subjects viewed the scene both onto the wall-screen and in-motion through the HMD. In immersive mode, they only viewed the scene in-motion through HMD. Average velocity of center of pressure (V) was recorded. Each trial lasted 51.2 s and was repeated 3 consecutive times.

Results: Difference between EO and EC was greater in OH than in AMDs and YH (p<.03). V was higher in immersive than in non-immersive mode (p<.01). There was no significant difference between AMDs and OH (p=.7). The postural effects generated by the HMD image did not differ according to groups or modes of presentation. (p=.4).

Conclusions: AMD patients demonstrated a smaller visual contribution to postural control than age-matched healthy subjects. Visual motion generated by the HMD did not induce stronger balance disruption in AMD patients than in healthy subjects, and never exceed sway in EC. Furthermore, immersive condition generated more instability than non-immersive condition for all subjects.

Keywords: 549 image processing • 412 age-related macular degeneration