Purpose: The aim of this study was to investigate the relationship between clinical macular changes and retinal function in age-related macular degeneration (AMD).
Methods: We recruited 357 participants with visual acuity of better than 20/60 in the study eye, including 64 individuals with normal fundi and 293 AMD participants classified into 12 subgroups based upon the International Classification and Grading System. Visual function in the study eye was assessed using two steady-state tests (achromatic 14 Hz flicker [F14Hz] and isoluminant blue color [BCT]) and two adaptation measurements (cone photo-stress recovery rate [CRR] and rod dark adaptation recovery rate [RRR]). The groups were compared on their average psychophysical measurements and ranked according to functional deficiency.
Results: Both adaptation parameters were significantly abnormal when only hard and/or intermediate drusen were evident (compared to controls, P < 0.023) and yielded considerably worse outcomes in cases with more advanced fundus changes (P < 0.001), but provided limited ability to discriminate between these cases (linear trend, CRR t = 0.68, P = 0.50 and RRR t = 1.76, P = 0.08). Steady-state measurements, however, declined gradually along the entire hierarchy of fundus changes (linear trend, F14Hz t = 10.16, P < 0.001 and BCT t = 11.19, P < 0.001) with F14Hz being able to detect significant functional change as early as in the intermediate drusen group, when compared to controls (P = 0.003).
Conclusions: Steady state thresholds (F14Hz and BCT) and clinical signs showed significant concordance across the spectrum of early AMD fundus changes. This suggests that these tests may be an effective tool for monitoring progression of AMD to supplement clinical grading.