The Development Of The Preferred Retinal Locus In Macular Disease

Abstract

Abstract: : Purpose: Patients with macular disease and central scotomas must use a peripheral, preferred retinal locus (PRL) in place of their damaged fovea for visual tasks. The mechanism by which the PRL develops is not fully understood. This study investigates the development of the PRL over the first twelve months after onset of dense scotoma in the second eye of patients with macular disease. Methods: Twenty patients with age–related macular disease (AMD) and five with juvenile macular disease (JMD) were recruited. All patients had developed a scotoma in their better eye within the previous two weeks. Patients attended for baseline assessment within two weeks of recruitment and for up to 5 repeat visits over the next 12 months. At each visit, best corrected visual acuity and contrast sensitivity were recorded. Scotoma size and fixation characteristics were determined using a scanning laser ophthalmoscope. An infrared gazetracker was used to record eye movements during fixation, a saccade task and reading. Reading speed was measured using MN–Read style sentences displayed on a monitor at three times threshold acuity size. Results: At the exit point from the study, reading speed had improved by more than 10% in 9 of the patients (36%), deteriorated by more than 10% in 10 patients (40%) and remained constant in the remaining 6 patients. PRL location was not associated with reading speed at baseline or exit from the study. Half of the patients changed their principal PRL location over the course of the study. There was no difference in reading speed between those who changed their PRL and those who did not. Lack of awareness of PRL use ("pseudofoveation," where patients describe themselves as looking straight ahead when using their PRL) was the most significant predictor for improved reading speed: reading speed increased by 25%, on average, in the patients who had pseudofoveated and fell by 45% in patients who did not pseudofoveate. Median time to pseudofoveate was 1 month for JMD patients and 6 months for AMD patients. Conclusions: Patients reading speed can improve over time without any active intervention or training. Although reading speed does not appear to be affected by PRL location, pseudofoveation is an important indicator of successful adaptation. JMD patients make this adaptation more quickly than AMD patients. This information is of relevance for clinicians working in the rehabilitation of patients with macular disease.

Keywords: low vision • age–related macular degeneration • reading