Focal electroretinogram and microperimetry testing of photoreceptor-retinal pigment epithelium function in intermediate age-related macular degeneration

Purpose: To compare the performance of focal electroretinogram (FERG) and fast mesopic microperimetry in evaluating macular function of intermediate age-related macular degeneration (iAMD) subjects with preserved visual acuity. Methods: Cross-sectional, observational study. Participants with drusen >125 µm and VA ≥80 ETDRS letters and age- and sex-comparable healthy subjects were consecutively enrolled in the study. Three photopic FERG recordings of the central 9° of the macula with luminance modulated stimuli flickering at 42.5 Hz and a fast mesopic microperimetry with a custom pattern of 3 central (CS) and 3 paracentral (pCS) stimuli at 1.2° and 6° from fixation were acquired. Results: Overall, 112 eyes of 77 participants (age 73.0 ± 7.1 years, 47 iAMD eyes) were analysed. Mean FERG amplitude, CS and pCS (all p < 0.05) were lower in the iAMD group. A significant association was observed between FERG amplitude and iAMD (OR 9.58, p < 0.001) in multiple logistic regression analysis. Z-scores of FERG were lower than microperimetry in iAMD (p = 0.002) but not for healthy participants. AUC of the ROC curve was greater for FERG than microperimetry (0.895 versus 0.644 and 0.675, both p < 0.05). Conclusion: Focal ERG objectively measures a cumulative response originating from the photoreceptor-RPE complex of the central 9° of the macula and demonstrated high accuracy in identifying decreased central macular function in iAMD patients with preserved visual acuity, performing better than fast mesopic microperimetry. Focal ERG should be considered a reliable technique for measuring retinal sensitivity of iAMD patients.