USING 2 PREFERRED RETINAL LOCI FOR DIFFERENT LIGHTING CONDITIONS IN PATIENTS WITH CENTRAL SCOTOMAS

Purpose, Using a scanning laser ophthalmoscope, it was found that some patients with relative central scotomas reliably used two different p referred retinal loci (PRLs) at different stimulus illuminances. This article describes adaptations in a patient's PRL for fixation when dim ming the stimulus increased the relative scotoma size. Methods. Twenty -eight patients with macular diseases had their dense and relative mac ular scotoma borders mapped with the scanning laser ophthalmoscope. Th e high-illuminance PRL (PRLhi) and low-illuminance PRL (PRLlo) were op erationally defined as the PRLs that patients used to fixate a high or low illuminance stimulus, respectively. The PRLs' abilities to do vis ual tasks and their characteristics at the corresponding illuminances were assessed. Results, The PRL consistently shifted between the PRLhi and the PRLlo as the stimulus illuminance was changed. Brightness per mitting, the visual system prefers to use the PRLhi with generally bet ter performance in visual function such as fixation stability. There w ere no significant differences between the PRLhi and the PRLlo in purs uit and saccadic abilities, when assessed by subjective ratings. The i lluminances that induced shifting ranged from 106 to 3437 trolands. Th e PRLhi was always located within an area of relative scotoma, usually at the fovea or just outside a dense scotoma. The PRLlo was located i n relatively healthy retinal area, and usually below or to the left of the PRLhi in the visual field. Conclusions. In the visual system, two well-defined PRLs can develop when visual function is adapting to mac ulopathy, with the use of each depending on the brightness of objects used in visual tasks. Rehabilitation and treatment strategies should c onsider the existence of multiple PRLs.