Optical coherence tomography angiography based assessment of macular vessel density, retinal layer metrics and subfoveal choroidal thickness in COVID-19 patients

ABSTRACT

Purpose: OCTA is a non-invasive imaging technique for assessment of retino-choroidal vasculature. It allows for the quantitative assessment of retinal microvasculature. This study evaluates macular vessel density (VD), foveal avascular zone (FAZ) area, subfoveal choroidal thickness (SFCT) and retinal layer metrics by optical coherence tomography angiography (OCTA) in COVID-19 recovered patients. Additionally we studied the correlation of OCTA parameters with severity and duration of COVID-19 disease, steroid administration, and vaccination status. Methods: It is a case-control study of 180 patients. OCTA parameters namely-superficial and deep VD in various sectors-total, superior, inferior, central, inner, superior-inner, inferior-inner, full;superficial and deep FAZ area;SFCT central subfield thickness (CST) were measured. Additionally, retinal layer metrics, including nerve fiber layer, ganglion cell layer-inner plexiform complex, inner nuclear layer, outer plexiform layer, and outer nuclear layer were compared between cases and controls. A correlation analysis of OCTA parameters was done with severity and duration of disease. Results: FAZ area (superficial and deep);retinal layer metrics including ganglion cell layer and inner plexiform layer, outer plexiform layer and outer nuclear layer showed significant reduction while there was a significant increase in SFCT in COVID-19 patients. Corticosteroid treatment resulted in significant decrease in VD. A positive correlation was elicited between FAZ area and disease duration;while VD correlated negatively with the duration of disease. Multivariate analysis showed significant relationship between superficial FAZ area, deep FAZ area and SFCT. Conclusions: OCTA showed alteration in retinal microvasculature and metrics in COVID-19 patients. Choroid being a highly vascular structure was also affected. There was a resultant alteration in FAZ area and SFCT. Moreover, thrombotic phenomenon associated with COVID could alter retinal layer metrics. Additionally, corticosteroids also appear to alter retinal microvasculature. This study could help understand the wide-spread thrombotic phenomenon often associated with COVID infection and predisposition for the same among specific patients.