As the list of symptoms linked to COVID-19 continues to expand and the infection’s association with vascular changes becomes more apparent, researchers decided to observe recently infected patients for possible retinal capillary changes.

In this case-control study, 69 patients between ages 18 and 55 who had contracted COVID-19 within the last three months were included. Subjects were divided into three groups: mild (asymptomatic or lightly symptomatic), moderate (admitted to the hospital but lacking acute respiratory distress) and severe (admitted to the ICU and developed an acute respiratory distress). The control group consisted of 27 subjects who tested negative for COVID-19.

All subjects underwent funduscopy and in-depth analysis of the vascular plexus using OCT angiography centered on the fovea to assess vascular density (VD).

At the macroscopic scale, no changes were observed in the vascular architecture of the superficial or deep plexus. There were also no visible anatomical alterations in terms of the size, shape or circularity of the foveal avascular zone. However, moderate and severe COVID subjects had decreased central VD, the researchers found, and suggested that “persistent hypoxemia and immune-mediated inflammatory milieu are the most plausible explanations for this phenomenon.” Parafoveal areas did not appear to show decreased vessel density, they noted, and funduscopic lesions were absent.

“Macroscopic lesions were expected to be found in the retina,” they say. “Subjects requiring admission in ICU, who received treatment with anticoagulant drugs and mechanical ventilation, were expected to show small hemorrhages or cotton wool exudates from small infarcts in the nerve fiber layer. However, normal fundus without hemorrhages, ischemic areas or exudates were observed.”

The study concludes patients with moderate and severe COVID-19 had decreased central retinal VD as compared with that of asymptomatic cases or control subjects. Longitudinal studies may be necessary to assess vascular outcomes in COVID-19, but this study demonstrates the complexity of the disease and how ocular changes are among its effects on the body.