Preferred Retinal Loci Relationship to Macular Scotomas: A10-Year Comparison

Abstract

Age-related maculopathy is the leading cause of vision loss among adults in developed countries, and its prevalence is expected to double over the next decade (Congdon et al., 2004; Friedman et al., 2004). The two forms of age-related maculopathy--exudative and nonexudative--are capable of affecting the macula, with potential symptoms including decreased contrast sensitivity, decreased visual acuity, abnormal adaptation to the dark, and central or pericentral scotomas (Jager, Mieler, & Miller, 2008). When a central scotoma impairs the ability of the fovea to distinguish detail, one or more preferred retinal loci (PRL) (Schuchard & Raasch, 1992; von Noorden & Mackensen, 1962; White & Bedell, 1990), also known as pseudo-foveas (Guez, Le Gargasson, Rigaudiere, & O'Regan, 1993), naturally develop at eccentric retinal locations and become the new points of fixation. The location of the PRL varies from person to person, as does the ability to maintain steady fixation with the PRL and to use it for reading and activities of daily living (Dalgleish & Naylor, 1963; Fletcher, Schuchard, & Watson, 1999; Timberlake et al., 1986; Whittaker, Budd, & Cummings, 1988). Fletcher and Schuchard (1997) reported the results of a study examining patterns of PRL ability and location relative to macular scotomas. They mapped dense scotomas and determined the location of the PRL in 1,339 eyes in 825 persons with a scanning laser ophthalmoscope during a standard low vision rehabilitation evaluation. Fletcher and Schuchard created a scoring system to measure the pursuit ability, fixation stability, and saccadic ability of the PRL. They determined the characteristics of dense scotomas within 2.5 degrees of the PRL or fovea. Of the 1,339 eyes, 84% (1,130) demonstrated an established PRL, ranging in size from 1.0 degrees to 9.0 degrees in diameter, and 82.5% had a central dense scotoma. The PRL had no dense scotomas on any border in 14.8% of the eyes. It had one, two, or three borders with a dense scotoma in 39.7%, 19.0%, and 9.0% of the eyes, respectively. Ring scotomas, bordering the PRL on four borders, were present in 17.4% of the eyes. Of the eyes with one scotomatous border, most had a field defect located either superior (39.0%) or to the right (33.7%). It was less common for the eyes to have field defects to the left or inferior, with 19.9% and 7.5% of the eyes, respectively. This report presents a 10-year comparison of these previous findings. It examines whether the PRL characteristics of persons with low vision remained steady over the ensuing decade. Changes in PRL and visual field characteristics among persons with low vision over time could have implications for the approaches of low vision rehabilitation professionals to training in eccentric viewing and other rehabilitation techniques. METHODS The study used 271 persons who were referred to the Frank Stein and Paul S. May Center for Low Vision Rehabilitation at California Pacific Medical Center (CPMC) in San Francisco between 2005 and 2007. All consecutive patients with low vision were included in the study, regardless of age, gender, race, and other demographic variables. Participants were excluded only if they lacked the cognitive or physical ability to complete a macular perimetry examination, as determined by the clinical impression of the ophthalmologist. Approval from the institutional review board was obtained from CPMC for the retrospective analyses of charts. As part of the standard low vision rehabilitation evaluation, an ophthalmologist measured visual acuity with the Early Treatment of Diabetic Retinopathy System chart (Ferris, Kassoff, Bresnick, & Bailey, 1982). The characteristics of the scotoma and PRL were measured with a Scanning Laser Ophthalmoscope (SLO; SLO-101, Rodenstock, Dusseldorf, Germany). The SLO was outfitted with a smart microperimetry (MacKeben & Gofen, 2007) program with a gaze-contingent display that automatically monitors eye movements, blinks, and other factors. …