Association of Self-Reported Task Difficulty with Binocular Central Scotoma Locations

Abstract

Purpose: To determine if the location of binocular central scotomas relative to fixation, predicts the difficulty that low vision patients are likely to have with driving, reading, and mobility tasks.

Methods: This study was conducted in accordance with the tenets of the Declaration of Helsinki and Johns Hopkins Institutional Review Board. Perimetry: Central scotomas were mapped with a video haploscope tangent screen in 284 patients. The haploscope consisted of 2 flat panel displays, one per eye, imaged at infinity through 9mm diameter exit pupils centered on the patient’s pupils. The patient’s refractive error corrections were incorporated into the optical paths. Infrared video cameras where used to monitor ocular alignment and fixation stability. The patient fused the two 50^o h x 40^o v displays and the fixation cross was imaged at the center of both displays, thereby providing binocular fixation, while test stimuli were presented monocularly at 43 locations in a 25^o square grid around fixation. Self Reported Difficulty Ratings: Patients rated difficulty of a subset of 120 reading, 50 mobility and 22 driving tasks in the Activity Inventory on a five point scale. Rasch analysis was used to estimate self-perceived ability for driving, reading and mobility for each patient. Analysis: Unpaired, two tailed t-tests were performed on distributions of each ability measure for each test location in the central field comparing patients who detected the stimulus to those who did not.

Results: Driving: Scotomas below and to the lower right of fixation and a single point 10^o above and to the right of fixation were associated with significant decreases in self-perceived driving ability. Reading: Scotomas from 7.5^o left of fixation to 12.5^o right of fixation and scotomas below and to the lower right of fixation were associated with significant decreases in self-perceived reading ability. Mobility: Scotomas below and to the upper right of fixation were most strongly associated with decreases in self-perceived mobility function.

Conclusions: Driving difficulty is associated with scotomas that fall on the instrument panel and rear view mirror when gazing straight ahead. Reading difficulty is associated with scotomas that could interfere with text preview and navigating to the next line. Mobility difficulty is associated with scotomas that could interfere with identifying information below the line of sight.

Keywords: 584 low vision • 642 perimetry • 669 quality of life