Ten-Year Parapapillary Gamma Zone Expansion and Axial Elongation in High Myopia Based on SS-OCT Imaging

Purpose: The parapapillary gamma zone is a hallmark structural change of the optic nerve head (ONH) in pathological myopia and is closely linked to axial elongation. Cross-sectional studies suggest strong correlations between gamma zone and axial length (AL), but longitudinal data characterizing gamma zone progression and its impact on AL are scarce. Methods: In this 10-year prospective study, 205 participants with bilateral high myopia (spherical equivalent ≤ -6.0 diopter [D]) from the Zhongshan High Myopia cohort were followed. A novel swept-source optical coherence tomography (SS-OCT)-based algorithm was developed for automated three-dimensional quantification of Bruch's membrane opening (BMO) displacement and gamma zone parameters, including area, angular extent, maximal radial extent, and spatial distribution. Associations among BMO and gamma zone metrics and myopia progression (AL, spherical equivalent, and AL change rate) were analyzed using linear and nonlinear regression. Results: The study included 205 individuals (mean age = 14.84 ±2 .26 years). In multivariate analysis, a larger area of BMO (mean = 3.65 ± 1.06 mm²) was associated with greater AL (P = 0.039) and inversely related with spherical equivalent (SE; P = 0.001). The gamma zone area (mean = 1.71 ± 2.20 mm²) was significantly correlated with AL (P < 0.001) and SE (P = 0.003) after adjusting for confounders. The gamma zone area was used to stratify the participants into four quartiles (Q1-Q4). Quartile Q4 showed a markedly greater rate of AL change than each of the lower quartiles (P < 0.0001), which remained evident even after Q1 to Q3 were merged. Conclusions: Progressive gamma zone enlargement is strongly associated with axial elongation in high myopia. Once the gamma zone exceeds a critical area threshold, the AL accelerates rapidly, likely reflecting compromised biomechanical counterforce from Bruch's membrane (BM). Longitudinal gamma zone monitoring may provide a valuable prognostic marker for identifying eyes at risk of accelerated and potentially irreversible myopic progression.