Concept of a functional retinal locus in age-related macular degeneration

Abstract

Purpose: Preferred retinal loci used for eccentric fixation in patients with age-related macular degeneration (AMD) may be different from the eccentric neighbouring loci of highest retinal sensitivity. This study was designed to highlight the conceptual difference between the 2 and the concept of a functional retinal locus encompassing both the preferred retinal locus and the locus with highest retinal sensitivity. Design: Prospective, nonrandomized, observational case series. Participants: We recruited 15 adults with documented AMD, low vision, and best-corrected visual acuity of 20/50–20/400 in the better eye. Methods: Automated microperimetry methods were used to assess topographic retinal sensitivity and location of preferred retinal loci. Results: Mean (SD) age for the group was 85.1 (6.5) years. Mean (SD) best-corrected visual acuity measured was 0.88 (0.25) logMar units (20/150). The mean (SD) eccentricity of the preferred retinal locus used forfixation was different from the eccentricity of the area with highest retinal sensitivity in the same eye (7.53° [2.47°] vs 9.30° [2.93°], respectively; p < 0.0003). The oculomotor efficiency score measured 82%. The mean (SD) retinal sensitivity at the preferred retinal loci was inferior to that of loci with highest retinal sensitivity (5.83 [4.26] vs 8.60 [3.06] dB, respectively; p < 0.0007). The highest correlation was measured between potential visual acuity estimates and estimates of retinal sensitivity at the highest retinal sensitivity loci ( p < 0.0048). Conclusions: Preferred retinal loci and highest retinal sensitivity loci are not identical in AMD cases. A new concept of functional retinal locus is proposed to define their relation. A new concept of an oculomotor efficiency score is proposed to define oculomotor abilities when macular function is lost.