COVID-19 Survivors Have Reduced Retinal Vessel Density, Study Shows

Nurses and doctors in protective workwear standing around hospital bed of grateful senior male patient applauding his strong recovery.
Researchers compared retinal images of coronavirus survivors and healthy controls.

Superficial and deep retinal capillary plexus (SCP and DCP, respectively) vessel density (VD) is lower in patients who have survived COVID-19, researchers found in a cross-sectional study published in Canadian Journal of Ophthalmology. The researchers sought to add to the limited body of research on retinal complications of coronavirus disease 2019 (COVID-19).

The researchers compared optical coherence tomography angiography (OCT-A) imaging from 31 physicians and nurses (14 females, mean age of approximately  40 years) from the Imam Reza Hospital who had recently recovered from COVID-19 with an age-matched (P =.115) control cohort of 23 nurses and physicians (14 males, mean age approximately 36 years) from the same hospital who were imaged using the same OCT-A machine in a previous study.

They collected each subject’s ocular, systemic and any COVID-19 history of symptoms, disease course and hospitalization. They excluded anyone with history of refractive or intraocular surgery, diabetes mellitus, auto-immune disease, current pregnancy, breastfeeding, or migraine, as well as anyone with absolute spherical refractive error greater than 5.00 D and cylindrical refractive error more than 2.0 0 D, glaucoma, retinal disease, ocular media opacity preventing high-quality imaging or reduced OCT-A scan quality (index less than 7/10), or best-corrected visual acuity less than 20/20.

The researchers obtained OCT-A scans with images centered on the fovea of each eye of the subjects and included the data from whichever eye produced better image quality. The area and perimeter circumference of the fovea avascular zone (FAZ), the foveal vessel density [FD]) and the vascular density (VD) of the fovea and parafovea, a 3 mm diameter ring around the fovea, at the level of the SCP and DCP were recorded.

The researchers performed multivariate linear and logistic regression analyses to address the effect of potential confounders on continuous and nominal dependent variables.

Mean quality scan index was approximately 7.64 in the COVID cases and 8.34 in the normal controls (P =.001). The mean whole-image SCP VD in the COVID-19 group (44.98 ± 4.16) was significantly lower than the mean SCP VD in the normal control group (48.36 ± 2.24) (P =.001). The mean whole-image DCP VD in the COVID-19 cohort (49.74 ± 3.39) was also significantly lower than the mean DCP VD of the control cohort (53.03 ± 3.29) (P =.001). The mean FAZ area in the COVID cohort (.27 +/- .11) was not significantly greater (P =.191) than the mean FAZ area in the control cohort (.24 +/- .08).

Controlling for quality scan differences, the whole image DCP VD all maintained statistically significant lower VD values vs controls. FAZ area and perimeter circumference were significantly greater after MANCOVA vs normal controls (P =.025, P =.016, respectively). Mean SCP VD was consistently lower in the hospitalized patients. Also, 4 COVID cases demonstrated apparent flow deficit, especially in the SCP.

Limitations of the study include possible ascertainment bias and “a slightly greater” scan quality in the normal controls.

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Abrishami M, Emamverdian Z, Shoeibi, N, et al. Optical coherence tomography angiography analysis of the retina in patients recovered from COVID19: A case-control study. Can J Ophthalmol. Published online November 14, 2020. doi:10.1016/j.jcjo.2020.11.006