An Autofluorescence-Based Computational Method to Evaluate Microperimetry Grid Test Patterns in Geographic Atrophy

Abstract

Purpose : Geographic atrophy (GA) is an advanced form of age-related macular degeneration characterized by progressive loss of outer retinal tissue over months to years. Microperimetry (MP) is a test of macular sensitivity and a functional outcome measure in GA. We designed a method to evaluate the effectiveness of a conventional MP grid test pattern in patients with GA.

Methods : Fundus autofluorescence (FAF) images were retrospectively obtained from patients with GA. We excluded images with poor quality due to media opacity, and images where atrophy or borders were indistinct. Areas of GA were segmented by a grader. Conventional 10-2 MP grids with 68 test loci were overlaid on images in Python. The main outcome measure was number of test loci located in the junctional zone (within 250 microns of a GA border).

Results : FAF images were obtained from 34 eyes of 21 patients. Mean age was 84.0 years (SD = 7.6). Fovea-involving GA was present in 14/34 (41%) eyes, and extrafoveal GA was present 20/34 (59%). Unifocal GA was present in 9/34 (26%) eyes, and multifocal GA was present in 25/34 (74%). Mean GA area was 4.3 mm² (SD = 5.5). A mean of 55.7 loci (SD = 14.4; IQR = 52.5–65.0) were external to GA lesions. A mean of 8.7 loci (SD = 4.2; IQR = 6.0–12.0) were located inside the junctional zone. The average locus-to-border distance was 873 microns (SD = 376; IRQ = 635–1065). For unifocal GA, the mean (SD) number of junctional zone loci was 5.8 (1.9), compared to 9.7 (4.3) for multifocal GA (Mann-Whitney U, P = 0.008). Mean (SD) number of junctional zone loci was 6.2 (2.8) for total lesion area less than 2.5 mm², 10.8 (3.1) for total lesion area 2.5 mm² to 7.5 mm², and 11.4 (4.8) for total lesion area greater than 7.5 mm² (Kruskall-Wallis, P = 0.002).

Conclusions : In patients with GA, a conventional 10-2 MP grid with 68 test loci has a small proportion of loci located in the junctional zone of GA. Many loci are located more than 500 microns from a GA border. There are more junctional zone loci when GA is multifocal, and when total lesion area is greater than 2.5 mm².

This abstract was presented at the 2024 ARVO Imaging in the Eye Conference, held in Seattle, WA, May 4, 2024.

 

Figure. Automated identification of microperimetry loci on a segmented fundus autofluorescence image. Blue, grader-segmented geographic atrophy. Purple, extralesional loci. Teal, junctional zone loci. Orange, intralesional loci. Red, foveal center.