Quantitative optical coherence tomography angiography of macular vascular structure and foveal avascular zone in glaucoma

Abstract

Objective: The study aimed to evaluate the quantitative characteristics of the macular vessel density (VD) and foveal avascular zone (FAZ) in glaucoma using optical coherence tomography angiography (OCT-A).

Design: Cross-sectional, age- and sex-matched case-control study.

Methods: Fifty-two eyes of 52 patients with primary open angle glaucoma and 52 eyes from 52 healthy participants were recruited retrospectively. OCT-A was performed on a 3 x 3-mm macular region centered on the fovea. OCT-A scans were manually graded to define the FAZ. Parafoveal VD in superficial and deep retina were analyzed in the circular- and quadrant-segmented zone. The FAZ parameters included size, perimeter, and circularity index. The regression analysis among VD and FAZ-related parameters and ocular parameters was performed, and the diagnostic ability was calculated with refractive error adjusted.

Results: For both groups, the mean age and the sex ratio was not different between groups. With refractive error adjusted, the average macular VD was lower in glaucoma than in the control group for superficial (P = 0.013), deep (P<0.001), and the whole retina (P = 0.002). There were increased FAZ perimeter and decreased FAZ circularity index in glaucoma when compared with controls (P<0.001). In the multivariate regression models, FAZ circularity index were significantly associated with decreased peripapillary RNFL thickness (P = 0.007) and macular GCIPL thickness (P = 0.009) measured by OCT. The refractive-error adjusted area under receiver operating characteristics was highest for FAZ circularity index (0.905; 95% CI, 0.844-0.966), followed by temporal deep retinal VD (0.870; 95% CI, 0.803-0.937) and FAZ perimeter (0.858; 95% CI, 0.784-0.932).

Conclusions: Decreased macular VD, increased FAZ perimeter, and decreased FAZ circularity index were observed in eyes with glaucoma using OCT-A. With refractive error adjusted, these parameters showed considerable diagnostic value for glaucoma. FAZ circularity index may be a novel biomarker representing disruption of the parafoveal capillary network in glaucoma, as supported by its association with structural parameters.

Fig 1. Macular vascular density at the different levels of 3 x 3-mm retinal vascular plexus.

(A) Superficial retinal vascular plexus in circular segmentation. (B) Superficial retinal vascular plexus in quadrant segmentation. (C) Deep retinal vascular plexus in circular segmentation. (D) Deep retinal vascular plexus in quadrant segmentation. For the circular segmentation, vascular density was calculated in three circular regions of different radius after excluding the adjacent inner circle area. Each region corresponding to C1, C2, and C3 had a 1.5-mm, 2-mm, and 2.5-mm radius from the center. The central area of 1-mm radius was excluded, most of which included the FAZ area. Similarly, quadrant segmentation was performed in four sectors, namely, temporal (T), superior (S), nasal (N), and inferior (I) in the region of 1-mm to 2.5-mm radius.

Fig 2. Representative cases with different foveal avascular zone (FAZ) assessment.

Two healthy cases (A, B) and four glaucoma cases (C, D, E, F). (A, B) Healthy eyes have a relatively smaller FAZ size and a higher circularity index. (C, D) Glaucoma patients with remarkable foveal capillary dropout, which is reflected in lower circularity index. (E, F) Advanced glaucoma patients with notably enlarged FAZ size (E) or distorted FAZ shape (F).

Fig 3. Refractive error-adjusted receiver operating curves for whole retina macular VD, FAZ perimeter, FAZ circularity index, peripapillary RNFL thickness, and macular GCIPL thickness.