Abstract
OBJECTIVE: To propose and evaluate the risk-stratification potential of Fundus Stretch Index (FunSI), a centile-based retinal metric that quantifies the geometric deviation of the fundus from what is expected for a given spherical equivalent refraction (SER). DESIGN: A population-based cohort study. PARTICIPANTS: Phakic eyes of 25 222 adults (SER: 0 D to –12 D) with adequate-quality fundus photographs at baseline (2009–2010), individually linked to routinely collected health records until 2022. METHODS: Quantile regression was used to estimate the 5th to 95th centiles of 10 dimensionless fundus imaging features (e.g., arterial/venous tortuosity and disc tilt), conditioning on SER. Fundus Stretch Index was computed as the sum of an eye’s SER-specific centile position across all imaging features, normalized to 0-1, such that an eye consistently ranked in the worst centile (fifth or 95th, depending on the direction of change as myopia increased) for its SER would have a value of 1. Cox regression was used to test the association between baseline FunSI and the risk of rhegmatogenous retinal detachment (RD), adjusting for baseline SER, age, sex, ethnicity, Townsend deprivation index, diabetes, hypertension, and ocular trauma; and primary open-angle glaucoma (POAG), adjusting for the same baseline covariates (excluding ocular trauma) plus intraocular pressure and corneal hysteresis. MAIN OUTCOME MEASURES: Rhegmatogenous RD and POAG onset. RESULTS: A total of 25 030 and 24 835 adults aged 40-69 years without any prior history of RD/breaks and glaucoma of any subtype were analyzed, respectively. The event rates (new cases per 10 000 person-years) were 4.9 for rhegmatogenous RD and 15.0 for POAG. Higher baseline FunSI was associated with an increased risk of developing rhegmatogenous RD (adjusted hazard ratio per 1 standard deviation [0.09], 1.26; 95% confidence intervals, 1.08-1.48; P = 0.004) and POAG (1.11; 1.01-1.22; P = 0.03). The addition of FunSI led to a much clearer improvement in the concordance index for the rhegmatogenous RD model compared with the POAG model. CONCLUSIONS: Fundus Stretch Index is an explainable approach to characterizing myopia at the retinal level. Two individuals may share similar baseline risk factors such as SER, but an overall geometric difference in their fundi, as quantified by FunSI, may reveal a difference in their long-term risk of sight-threatening diseases. FINANCIAL DISCLOSURES: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.