Comparison of the Peripapillary Structure-Vessel Density Relationship Before and After Axial Length Magnification Correction Using Different Methods.

Abstract

Background: To evaluate changes in OCTA-derived structural and vascular parameters before and after axial length (AL) magnification correction using two different formulas, and to explore their correlations with vessel density (VD).

Methods: This study included 45 high myopic eyes and 45 age- and gender-matched controls. Both 6 × 6 mm² optic nerve head imaging and biological measurement were performed using OCTA. Magnification correction was performed using both the Bennett formula and the device's built-in algorithm. Parameters analysed included retinal nerve fibre layer (RNFL) thickness, superficial vascular complex (SVC) VD, deep vascular complex (DVC) VD, and choroidal VD.

Results: In long AL eyes, uncorrected values underestimated RNFL thickness and SVC VD but overestimated DVC VD and choroidal VD; discrepancies increased with AL. The opposite pattern was observed in shorter eyes. After correction, all vascular parameters except DVC VD showed significant changes in the high myopia group, while non-high myopic eyes showed no significant differences. The two correction methods showed strong agreement across all layers. RNFL thickness correlated strongly with SVC VD, and choroidal thickness (CT) with choroidal VD, both before and after correction. Post-correction, AL was no longer associated with RNFL thickness or SVC VD, while its correlation with CT and choroidal VD persisted. Mediation analysis showed AL fully mediated the CT-choroidal VD relationship, with a stronger effect post-correction.

Conclusions: Magnification correction is crucial in high myopic eyes. Both formulas showed high consistency. Correction eliminated AL's confounding effects on RNFL and SVC VD, while emphasising its mediating role between CT and choroidal VD.