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

Abstract

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. Retrospective cohort study. 405 treatment-naïve RVO eyes. 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. 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. 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. 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.