Swept-source OCTA assessment of iris vasculature as a biomarker for myopic macular degeneration severity

To investigate the vessel area density (VAD) and morphological features of the iris in patients at different stages of myopic macular degeneration (MMD) using swept-source optical coherence tomography angiography (SS-OCTA).

In this retrospective case-control study, 106 eyes of 106 high myopia patients (axial length (AL) ≥26 mm) were included and classified into different MMD categories according to the International META-PM Classification. The VAD of iris, iris volume (IV), area of anterior iris surface (IS), area of posterior IS, and average iris thickness (IT) were evaluated using SS-OCTA. Associations among iris vasculature, iris morphology, and MMD categories were investigated.

Full-range, inner-region, and intermediate-region VAD of the iris decreased significantly with increasing MMD severity (all P-trend <0.001), whereas outer-region VAD did not show a significant linear trend. The area of IS was larger in eyes with MMD 2 and MMD 4 compared to the other two groups (all P <0.05). The full-range and outer-region VAD of iris was negatively correlated with AL, while the inner-region VAD of iris was positively correlated with the area of anterior and posterior IS, especially in eyes with MMD 2 (all P <0.05). Multivariate linear regression revealed that greater full-range, inner-region and intermediate-region VAD were all significantly associated with milder MMD, whereas greater outer-region VAD was significantly associated with shorter AL.

Iris blood flow, quantified by VAD, decreased with increasing MMD severity. Iris VAD may represent a promising candidate biomarker for non-invasive monitoring of MMD severity. Additionally, the association between VAD and AL or iris morphology varied across MMD categories.