Macular Edema Resistance in Retinal Vein Occlusion and the Protective Role of PAMM Subtypes

Purpose: To characterize eyes without macular edema (ME) at presentation in retinal vein occlusion (RVO), evaluate incidence and predictors of ME during follow-up, and assess the prognostic significance of paracentral acute middle maculopathy (PAMM) subtypes. Design: Retrospective cohort study. Participants: 405 treatment-naïve RVO eyes. Methods: Clinical and imaging features were compared between eyes with and without baseline ME. PAMM was classified as arteriolar, fern-like, or globular. Peripheral ischemia was quantified using ultra-widefield fluorescein angiography. Main Outcome Measures: Predictors of ME at baseline and during follow-up identified with logistic and Cox regression. Cumulative ME risk in eyes with PAMM assessed with Kaplan–Meier and multinomial regression analyses. Results: At baseline, 72 eyes (18%) were ME-free. These eyes were younger (49.8 ± 16.6 vs. 65.8 ± 13.6 years), more frequently had CRVO (85% vs. 50%), and fewer systemic comorbidities. PAMM was a strong protective factor against baseline ME (OR 0.05; statistically significant). During follow-up, cumulative ME incidence reached 42% at 1 year and stabilized thereafter. Higher baseline central macular thickness (HR 2.39/100 µm; statistically significant) and ischemic index (HR 1.03/1%; statistically significant) were risk factors, while age <50 years and early anti-VEGF therapy were protective. Globular PAMM, frequently associated with a cilioretinal artery, identified the lowest ME risk profile. Conclusions: Younger patients with CRVO often present without ME. Although nearly half of these eyes develop ME over time, baseline imaging—particularly presence and subtype of PAMM—helps stratify risk. Globular PAMM defines a paradoxical ischemic profile with preserved vascular integrity and minimal susceptibility to fluid accumulation.