Visual function and distribution of the preferred retinal loci in patients with AMD

Abstract

Purpose: Patients with AMD adapt to loss of central vision by developing preferred retinal loci (PRLs) in the eccentric, functional part of their retina. A PRL serves as a pseudo-fovea and is used in performing visual tasks. PRLs typically occur close to the border of the scotoma and most are in locations that correspond to the lower and left visual fields (VFs). This is a retrospective, observational case series study that examines whether visual acuity and ocular motor control during fixation correlates with the PRL’s location in the VF and whether the frequency distribution of the PRL locations differs for the better-seeing (BE) and the worse-seeing (WE) eye.

Methods: A total of 137 eyes with AMD were included; based on their acuity measures, 88 were BE and 49 were WE. Visual acuity was measured at 6m. Fixation stability, PRL location, and PRL distance from the former fovea were evaluated with the MP-1 microperimeter. Fixation stability was measured with a bivariate contour ellipse area (BCEA). PRL location was categorized based on 5 areas in the VF: central, superior, inferior, left, and right.

Results: For the BE, the PRL frequency distribution was significantly different for the 5 locations, χ²(4)= 19.9, p= .001. Most PRLs occurred in the inferior (31%) and left (32%) VFs, and the least in the right (7%) VF. Acuity and BCEA were best for PRLs in the central and superior VF, but PRL distance from the former fovea was smallest in these locations. Acuity and BCEA in the inferior VF were similar to those in the left VFs. Acuity correlated with BCEA and PRL eccentricity in the inferior VF [r(25)=0.51, p=0.007, and r(25)=0.47, p=0.013, respectively] and left VF [r(26)=0.55, p=0.003, and r(26)=0.40, p=0.033 respectively], but not in the superior or right VF.<br /> For the WE, the PRL frequency distribution was not different for the 5 locations. Acuity correlated only with PRL eccentricity in the inferior VF [r(9)=0.65, p=0.031]. No other relationships were significant.

Conclusions: The PRL occurs most frequently in functional VFs that are preferred for locomotion and left-to-right reading although a PRL in the left VF is not adequate for reading. The relationship between BCEA and acuity provides valuable information for rehabilitation, but should be applied only for the BE.