Intrasession Repeatability and Interocular Symmetry of Foveal Avascular Zone and Retinal Vessel Density in OCT Angiography

Transl Vis Sci Technol. 2018 Jan 19;7(1):6. doi: 10.1167/tvst.7.1.6. eCollection 2018 Jan.


Purpose: To measure intrasession repeatability and interocular symmetry of the foveal avascular zone area (FAZA) and superficial retinal vessel density (SRVD) using AngioVue Analytics optical coherence tomography angiography (OCTA).

Methods: Fifty healthy individuals were prospectively enrolled. OCTA scans (3 × 3 and 6 × 6 mm) were acquired twice in right and once in left eyes. FAZA (with and without rescaling) and SRVD for 18 regions (whole, fovea, parafovea, six parafoveal subregions, and nine square zones) were compared between two scans in right eyes (repeatability) and between both eyes (symmetry). Coefficients of repeatability (CRs) and limits of agreement (LAs) were calculated.

Results: Axial length-based image size rescaling had negligible impact on the intrasession CR of FAZA in both 3 × 3- and 6 × 6-mm images. The intrasession CRs for the foveal SRVD were 3.3% and 6.1% in the 3 × 3- and 6 × 6-mm OCTA images, respectively. Age and axial length did not influence test-retest variability of FAZA or SRVD. The interocular LAs in FAZA (0.039-0.059 mm2) was comparable to its CR. However, the interocular LAs in foveal SRVD were -4.5% to +3.8%, with 13% of the cohort showing an interocular difference greater than the CR.

Conclusions: FAZA repeatability is not influenced by image size correction, and foveal SRVD is more variable in 6 × 6- than 3 × 3-mm OCTA images. Low image quality may contribute to interocular SRVD asymmetry.

Translational relevance: CRs and LAs can be used to set a threshold for true changes in FAZA and SRVD in longitudinal studies of healthy individuals.

Keywords: coefficient of repeatability; OCTA; limits of agreement; normative data; retinal angiography; retinal capillary density; split- spectrum amplitude decorrelation angiography; test–retest variability.