Latitudinal variation in morphological patterns of lens opacity among patients with cataracts.

To characterize age-related cataract (ARC) morphology and subtype distribution across Yunnan (China), Vietnam, and Sri Lanka, and to assess associations with region, age, sex, and preoperative best-corrected visual acuity (BCVA). We reviewed 390 patients (657 eyes) who underwent phacoemulsification with IOL implantation at tertiary eye hospitals in Yunnan, Vietnam, and Sri Lanka from 2019-2024. traumatic, congenital, metabolic, or secondary cataracts (e.g., post-uveitic), and combined procedures (e.g., cataract-glaucoma surgery). ARC subtypes were classified using LOCS III as pure cortical (CC), nuclear sclerotic (NSC), posterior subcapsular (PSC), or mixed (e.g., CC/NSC, CC/PSC). We collected demographics, preoperative BCVA (decimal notation), ocular comorbidities, and surgical indications. Regional differences were tested with ANOVA or Kruskal-Wallis; correlations used Spearman's rank test (α = 0.05, two-sided). A sensitivity analysis used one eye per patient-selected as the more advanced cataract-to address bilateral inclusion. ARC subtype distribution differed significantly by region (χ2 = 105.33, df = 12, p < 0.001). CC/PSC was most common in Yunnan (34.7%) and Vietnam (56.6%); Sri Lanka had the highest proportion of pure CC (31.9%) and CC/NSC. Mean preoperative BCVA was better in Yunnan (0.43 ± 0.23), intermediate in Sri Lanka (0.25 ± 0.25), and worse in Vietnam (0.19 ± 0.24); all pairwise differences were significant (ANOVA F = 36.65, p < 0.001; Kruskal-Wallis H = 79.58, p < 0.001). Females comprised 60-68% of cases across regions. Age correlated positively with NSC (r = 0.37, p = 0.008) and CC/NSC (r = 0.47, p = 0.001). BCVA correlated inversely with mixed cataracts (r = - 0.67, p < 0.001) and pure PSC (r = - 0.32, p = 0.021). All key findings held in the single-eye sensitivity analysis (p < 0.001 for both BCVA and subtype distribution). ARC morphology differs markedly across Yunnan, Vietnam, and Sri Lanka-CC/PSC dominates in Yunnan and Vietnam; pure CC and CC/NSC predominate in Sri Lanka. These patterns may reflect regional differences in UV exposure, nutrition, healthcare access, or genetic background. As a retrospective observational study, causal inference is limited-but the findings provide clear, testable hypotheses for future prospective research.