Distinguishing Dry vs. Wet AMD With 3-D Computer-Automated Threshold Amsler Grid Test

Abstract

Purpose: : To study non-exudative (dry) and exudative (wet) age-related macular degeneration (AMD) with the 3-D computer-automated threshold Amsler grid (3D-CTAG; Fink and Sadun, J Biomed Opt 2004).

Methods: : 63 AMD (34 dry, 29 wet) eyes were tested with paper Amsler Grid and 3D-CTAG at 5 contrast levels (5%, 10%, 20%, 40%, and 100%). Indices used to analyze the findings were: Lost Area Grade (LAG) = (scotoma area at highest tested contrast level / scotoma area at lowest tested contrast level) x scotoma depth [%]; Preserved Area Grade (PAG) = (intact visual field area at lowest contrast level / intact visual field area at highest contrast level) x scotoma depth [%]; and Difference Area Grade (DAG) = |PAG - LAG| to quantify scotoma shape.

Results: : 25/34 (74%) dry AMD and 6/29 (21%) wet AMD eyes had no abnormalities on the paper Amsler grid. Of these, 5/25 (20%) dry AMD eyes exhibited defects when tested with 3D-CTAG and all 6/6 (100%) wet AMD eyes had defects when tested with 3D-CTAG.Dry AMD exhibited cylindric 3D scotomas at lower contrast, which were absent at higher contrast levels (i.e., relative scotomas). Wet AMD eyes had large scotomas at low contrast, then a step-down progression of smaller cylindric defects at increasing contrast levels (i.e., small central absolute scotomas with surrounding relative scotomas).The mean number of defects observed with 3D-CTAG was 0.44 for dry AMD and 1.24 for wet AMD (p = 3.15e-5). The mean LAG was (29.50 ± 41.73)% for dry AMD vs. (66.74 ± 30.91)% for wet AMD. Mean PAG was (36.18 ± 47.49)% for dry AMD and (89.32 ± 21.06)% for wet AMD. Mean DAG was (6.68 ± 15.19)% for dry AMD vs. (22.58 ± 26.44)% for wet AMD (p = 0.006).

Conclusions: : 3D-CTAG increased the sensitivity for the detection of wet AMD from 79% to 100% and discriminates between wet and dry AMD. Wet AMD had more defects and a larger difference between the LAGs and PAGs. The shape of wet AMD 3D-CTAG scotomas is likely due to central neovascular membranes surrounded by edema. Adding a third dimension to central visual field testing enables quantification of relative scotomas to further characterize edema on a functional level. Furthermore, characterizing the shape of scotomas by 3D-CTAG may provide a quantitative outcome measure for therapies directed at treating leakage and edema in patients with AMD.

Keywords: age-related macular degeneration • contrast sensitivity • visual fields