Assessment of the foveal avascular zone morphology in healthy subjects using swept-source optical coherence tomography angiography.

Abstract

Purpose : To study the morphology of the foveal avascular zone (FAZ) from optical coherence tomography angiography (OCTA) utilizing manual and automatic methods.

Methods : Prospective IRB-approved study in 43 healthy subjects with a normal eye exam who underwent OCTA imaging. 3x3 mm macular scans were obtained with swept-source OCTA imaging (PlexElite 9000, Zeiss, Dublin, CA). One eye per subject was included for analysis. Scans with signal strength <7 and motion artifacts through the FAZ were excluded.

FAZs were manually traced in ImageJ (NIH, Bethesda, MD) by three trained graders (NHF, CAH, and REH) and analyzed for area (mm²), circularity and roundness indexes. In addition, OCTA scans were analyzed for FAZ area and circularity by the Advanced Retinal Imaging (ARI) network (Zeiss) proprietary algorithms. Paired t tests were used to compare methods. Statistical analysis and intraclass correlation were performed by SPSS version 27.0 (IBM, Armonk, NY, USA).

Results : 43 eyes met inclusion criteria. The mean FAZ area by manual tracing was 0.27 mm² (SD±0.15). The mean area for the three graders were 0.27 ±0.15, 0.27 ±0.15, and 0.26 ±0.15; single measures intraclass correlation coefficient (SMICC) was 0.99. The mean FAZ area by ARI algorithms was 0.24 ± 0.19. FAZ area as measured by manual (average of graders) and ARI was not significantly different (p=0.25).

The mean circularity by manual tracing was 0.52 ±0.12. The mean circularity for the graders were 0.56 ±0.12, 0.46 ±0.12, and 0.54 ±0.14; SMICC was 0.85. The mean roundness by manual tracing was 0.82 ±0.12. The mean roundness for graders were 0.82 ±0.11, 0.81 ±0.13, and 0.82 ±0.13; SMICC was 0.94. The mean circularity by ARI was 0.75 ±0.099. Manual FAZ circularity was less than ARI circularity (p<0.0001), while manual roundness was greater than ARI circularity (p<0.01).

Conclusions : Our study provides FAZ metrics in normal subjects as assessed by OCTA. We demonstrate high intraclass correlation among manual grading methods. Given its higher intraclass correlation coefficient, roundness may be a preferred metric over circularity in the assessment of FAZ circularity.

This is a 2021 Imaging in the Eye Conference abstract.

 

Figure 1. FAZ area (left) and circularity indexes (right) of 43 healthy subjects by manual (ImageJ) and automated (ARI) methods. ARI, Advanced Retinal Imaging.