Early macular microvascular attenuation in moderate myopia: projection artifact-removed and magnification-corrected optical coherence tomography angiography in an Iranian adult cohort.

BACKGROUND

This study aimed to evaluate macular and peripapillary optical coherence tomography angiography (OCTA) parameters in mild and moderate myopic eyes compared with emmetropic controls, utilizing built-in projection artifact removal (PAR) and rigorous magnification correction.

METHODS

This prospective cross-sectional study included 218 eyes (90 emmetropic, 59 mild myopic, and 69 moderate myopic) of adults aged 20-52 years. Macular and optic disc OCTA scans were acquired using the RTVue-XR Avanti system with the built-in 3D-PAR algorithm enabled. Lateral magnification correction was performed post-hoc using the full Littmann-Bennett method ([Formula: see text]), with quadratic scaling applied to area measurements to ensure absolute mathematical precision. Eyes with axial length (AL) > 25.8 mm were excluded to minimize segmentation artifacts associated with posterior staphyloma and globe deformation.

RESULTS

Deep macular vessel density (VD) demonstrated a significant stepwise reduction across groups: emmetropia (45.92% ± 8.83) → mild myopia (41.44% ± 7.94) → moderate myopia (39.64% ± 10.74) (ANOVA P < 0.001). In contrast, superficial macular VD showed no statistically significant difference between mild myopia and emmetropia, with a significant decline observed only in moderate myopia (P < 0.05). The Foveal Avascular Zone (FAZ) area was significantly enlarged in moderate myopia (0.35 ± 0.12 mm², P < 0.001) but remained stable in mild myopia. In multivariable regression, spherical equivalent (SE) was the dominant independent predictor of deep VD reduction (Standardized β = -0.41, P < 0.001).

CONCLUSIONS

Retinal microvascular attenuation appears to begin early in the deep capillary plexus (even in mild myopia), whereas superficial plexus and FAZ changes are features of more advanced severity. These findings suggest that DCP vessel density is a sensitive population-level indicator of early pathophysiological remodeling, although its current diagnostic utility for individual clinical monitoring is limited by measurement variability relative to the effect size.