Evaluation of the Iris Vessel Density for Primary Glaucoma Diagnosis Using Anterior Segment Optical Coherence Tomography.

Introduction: This study aimed to evaluate the iris vessel density within a 15 mm × 12 mm area in primary glaucoma using anterior segment optical coherence tomography (AS-OCT) and anterior segment optical coherence tomography angiography (AS-OCTA).

Methods: The study involved 30 normal eyes and 31 eyes with primary glaucoma, comprising 15 with primary open-angle glaucoma and 16 with primary angle-closure glaucoma. OCT/OCTA images of the iris obtained were evaluated and a univariate logistic regression model was used to assess the correlation between the iris vessel density and primary glaucoma, area under the receiver operating characteristic (AUROC), and clinically relevant performance metrics of different regions (superior, inferior, temporal, and nasal regions) were compared. Additionally, the trabecular iris angle (TIA) in both the nasal and temporal regions to elaborate the mechanism of using iris vessel density for primary glaucoma detection.

Results: Across all regions, the vessel density in the glaucoma group was significantly lower than in the normal eyes. The nasal 6-12 mm annular region of the iris demonstrated the highest diagnostic ability (AUROC = 0.870, p < 0.001), followed by the temporal 3-6 mm annular region (AUROC = 0.837, p < 0.001). All AUROC exceeded 0.8, with p values below 0.01, indicating strong diagnostic accuracy. Furthermore, TIA in primary glaucoma was smaller than normal individuals. Compared with the nasal region, the temporal region exhibited higher correlation with TIA, where TIA500 demonstrated the largest diagnostic value in the temporal region (AUROC = 0.995, p < 0.001). Moreover, a strong correlation was observed between iris vessel density and TIA in the 6-12 mm region. Based on the clinical parameter metrics, the detection ability of iris vessel density in the nasal region and TIA in the temporal region are more significant.

Conclusion: Iris vessel density is significantly reduced in primary glaucoma. The wide-field AS-OCTA of iris provides a comprehensive perspective of microvascular structures, facilitating precise comparison and evaluation of vessel changes in different regions associated with glaucoma. Specifically, the vessel density in the larger annular region on the nasal region has significant diagnostic value, enhancing understanding of disease mechanisms and progression.