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

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 for fixation was different from the eccentricity of the area with highest retinal sensitivity in the same eye (7.53 degrees [2.47 degrees ] vs 9.30 degrees [2.93 degrees ], 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.