Regional variations in type 1 retinopathy of prematurity: GHANAROP and SUNDROP

Background/aims: To compare the incidence of Zone I Stage 3 retinopathy of prematurity (ROP) without Plus disease between diverse cohorts. Methods: 1164 premature infants (716 from the Stanford University Network for Diagnosis of Retinopathy of Prematurity (SUNDROP) in the USA and 448 from GHANAROP in Ghana) underwent telemedicine ROP screening from January 2023 to March 2025. Retinal images were prospectively graded by the same expert grader using International Classification of Retinopathy of Prematurity, third edition terminology. Treatment-warranted ROP (TW-ROP) was defined as type 1 ROP or aggressive ROP. The telemedicine ROP Severity Score (tROP-SS) was quantified for each examination. Incidence of Zone I Stage 3 without Plus disease, correlation between Plus disease and TW-ROP and correlation between Stage and Plus versus tROP-SS in Zone I disease were analysed. Results: 40% of treated eyes in GHANAROP versus 7.5% in SUNDROP (p=0.002) were Zone I Stage 3 without Plus. Treatment rates were similar between cohorts (2.2%–2.8%), although GHANAROP patients were significantly older (gestational age: 31 years, 2/7 vs 28 years, 5/7; p<0.001) and heavier (1352 g vs 1161 g; p<0.001) at birth. Correlation between Plus disease and TW-ROP was stronger in SUNDROP (Kendall’s Tau 0.73 vs 0.46, both p<0.001). In Zone I disease, Stage correlated poorly with Plus in both cohorts but strongly with tROP-SS (Kendall’s Tau ≥0.90, p<0.001). Conclusions: Zone I Stage 3 ROP without Plus is more prevalent in the Ghanaian cohort, challenging the assumed centrality of Plus disease for intervention in certain populations. Integrated scoring systems incorporating Zone, Stage and Plus may be crucial for accurate ROP classification, especially in low- and middle-income countries with zone-dominated disease.