Acircularity index and axis ratio of the foveal avascular zone in diabetic eyes and healthy controls measured by optical coherence tomography angiography

Abstract

Given the complexity of the current system used to stage diabetic retinopathy (DR) and the risks and limitations associated with intravenous fluorescein angiography (IVFA), noninvasive quantification of DR severity is desirable. We examined the utility of acircularity index and axis ratio of the foveal avascular zone (FAZ), metrics that can noninvasively quantify the severity of diabetic retinopathy without the need for axial length to correct for individual retinal magnification. A retrospective review was performed of type 2 diabetics and age-matched controls imaged with optical coherence tomography angiography (OCTA). Diabetic eyes were divided into three groups according to clinical features: No clinically observable diabetic retinopathy (NoDR), nonproliferative diabetic retinopathy (NPDR), and proliferative diabetic retinopathy (PDR). OCTAs of the superficial and deep vascular layers centered at the fovea were superimposed to form a full vascular layer on which the FAZ was manually traced. Acircularity index and axis ratio were calculated for each FAZ. Significant differences in acircularity index were observed between all groups except for controls vs. NoDR. Similar results were found for axis ratio, although there was no significant difference observed between NPDR and PDR. We demonstrate that acircularity index and axis ratio can be used to help noninvasively stage DR using OCTA, and show promise as methods to monitor disease progression and detect response to treatment.

Optical coherence tomography angiography analysis of foveal microvascular changes and inner retinal layer thinning in patients with diabetes

“…After controlling for confounding factors, we found that parafoveal vessel density and FAZ circularity index were independently related to mGCIPL thinning in the present study (table 3). Similarly, previous studies have suggested that changes in the FAZ circularity index13 and parafoveal vessel density12 are more reliably correlated with microcirculation impairment in DR. FAZ size shows high variability in healthy eyes, and it is affected by individual differences in ocular magnification such as variation in axial length 21. To our knowledge, this is the first study to report the relationship between changes of OCTA-derived microvascular parameters and mGCIPL thickness in patients with T2DM.…”

“…The FAZ area is enlarged in both DR and retinal vein occlusion due to destruction of the vascular arcades 7 11. Prior studies have qualitatively demonstrated that the FAZ becomes more a circular in DR, with effects on the FAZ perimeter and circularity index 13. Thus, loss of FAZ circularity is a good indicator of vascular dropout, and is associated with disease progression in vascular maculopathy 15.…”

Implication of Deep-Vascular-Layer Alteration Detected by Optical Coherence Tomography Angiography for the Pathogenesis of Diabetic Retinopathy

“…In contrast, another group reported increased fractal dimension in both vascular layers of patients with NPDR compared to control subjects [23]. In patients with PDR, significant FAZ area enlargement and a decrease of FAZ circularity and vessel density was detected in both superficial and deep vascular layers [28]. …”

An evidence‐based approach to the routine use of optical coherence tomography

“…Capillary closure may occur in early stages of DR, worsening as DR progresses; thus measurements such as FAZ size could potentially represent biomarkers for DR progression . Krawitz et al found a strong correlation between acircularity of the FAZ and the presence of DR.…”