Five-Year Changes in Pachydrusen with Late-Phase Hyperfluorescence on Indocyanine Green Angiography

Background/Objectives: Pachydrusen are a drusen subtype associated with the pachychoroid disease spectrum; however, their long-term natural history and pathophysiological significance remain unclear. We investigated 5-year morphological and topographic changes in pachydrusen using diagnostic criteria incorporating late-phase indocyanine green angiography (ICGA) hyperfluorescence. Methods: This retrospective observational study included fellow eyes with pachydrusen from patients with unilateral neovascular age-related macular degeneration. Pachydrusen were defined as sub-retinal pigment epithelium (RPE) deposits ≥ 125 µm in size with corresponding hyperfluorescence on late-phase ICGA. Lesion number, size, and spatial distribution (ETDRS grid and quadrant-based classification) were evaluated at baseline and 5 years. The incidence of macular neovascularization (MNV) and its colocalization with pachydrusen were assessed. Results: Among 57 fellow eyes with pachydrusen, incident MNV developed in 8 eyes (14.0%) during follow-up; the mean time to onset was 25.6 ± 16.3 months. No clear colocalization between pachydrusen and incident MNV was observed. Nineteen eyes completed the 5-year follow-up period. Pachydrusen were predominantly located outside the 6000 µm ETDRS grid at baseline (63.4%) and 5 years (66.3%), significantly exceeding the expected proportion based on the area ratio (p < 0.001). The lesions were most frequently observed in the superotemporal quadrant (52.6%). Over 5 years, 19.8% of the lesions increased in size, 67.2% remained stable, and 12.9% regressed; none of the regressed lesions were accompanied by RPE atrophy. Conclusions: Pachydrusen, defined as late-phase ICGA hyperfluorescence, was predominantly distributed outside the ETDRS grid with a superotemporal predilection and could increase or decrease over a 5-year follow-up period. No colocalization with MNV was observed, and no accompanying RPE atrophy after pachydrusen regression was identified, suggesting that late-phase ICGA-hyperfluorescent pachydrusen may represent a pathophysiology distinct from that of soft drusen.