Abstract
Abstract: :
Purpose: Most patients with age related macular degeneration (AMD) and dense central scotomas in both eyes adopt a preferred retinal locus (PRL) for eccentric viewing. The majority of patients place their PRL to the left or right of their scotoma in visual field space. However it is postulated that the optimal PRL position is inferior visual space as it provides a larger uninterrupted visual span for reading and mobility. The purpose of this study is to investigate which factors determine PRL location and specifically, whether the PRL develops in the area of peripheral retina with best visual acuity. Methods: Normal vision subjects (young and age matched) and patients with AMD (age 55–85 years) are being recruited. All AMD patients are tested on a Rodenstock scanning laser ophthalmoscope to identify the PRL location in their better eye. Foveal position in the AMD patients is determined by a previously described blind spot mapping technique (Kabanarou et al. ARVO 2002). A SMI EyeLink eyetracker is used to assess peripheral visual acuity in both groups. In the normal subjects a circular grid, with tumbling Landolt C optotypes, centred on the fovea with 8 points at each eccentricity of 2.5, 5, 7.5 and 10 degrees is used. A modified grid is used in the AMD patients. Results: In 8 normal subjects tested to date, the best visual acuity was along the horizontal meridian, at each eccentricity. There was no difference between oblique and vertical meridians. In 5 AMD patients, 2 placed their PRL in an island of intact retina inside the scotoma, 2 used PRLs below and right of their scotoma and 1 used a PRL below and left of their scotoma in visual field space. In all the AMD patients the PRL was located near the area of best visual acuity. Conclusions: For normal subjects it appears that visual acuity in the horizontal meridian is better than in oblique or vertical meridians. In AMD patients’ visual acuity is best near the PRL. We can not distinguish whether the PRL develops at the area of best visual acuity or if it improves at the PRL through practise. However it appears that visual acuity is an important factor in determining PRL location even when that location may not be optimal for everyday visual tasks.
Keywords: age–related macular degeneration • visual acuity • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials