Research continues to explore whether COVID can infiltrate the body through the eye and cause ocular symptoms. Looking further into this theory, a new study conducted in the Lombardy region of Italy discovered SARS-CoV-2 RNA on the ocular surface of patients with COVID-19, although the infectivity of the material couldn’t be determined. The investigators also detected the virus on the ocular surface of some patients whose nasopharyngeal swab results were negative.

The study investigated the prevalence of SARS-CoV-2 in tears collected from COVID-19 patients by polymerase chain reaction assays. The team conducted conjunctival swab testing on 91 hospitalized patients whose condition was clinically diagnosed by the assays on nasopharyngeal swabs, in addition to radiological imaging. Conjunctival swab testing was also performed on 17 healthy participants. Participants were an average of 59 years old, and the number of men and women in the study was similar.

SARS-CoV-2 was found on the ocular surface of 52 COVID-19 patients (57%), with a wide variability in mean viral load from both eyes.

In a subset of 41 patients, the investigators found a 63% agreement between positive conjunctival and nasopharyngeal swab test results when performed within two days of each other. In 17 of these patients, nasopharyngeal swab results were negative for SARS-CoV-2. On the other hand, conjunctival swab results were positive for the virus in 10 of the 17 patients.

The researchers cited different explanations for the presence of the virus on the ocular surface, but they stressed the reasons were speculative. For example, direct contagion from airborne droplets by infected people is possible, as well as from particles diffused in the atmosphere, they said. Atmospheric particulates are known to function as carriers for many chemical and biological contaminants, including viruses, they added.

Regarding other means of viral diffusion into the eye, the literature reports direct contact with infected surfaces by the hands followed by transport to the mouth, nose or other mucous membranes, such as the conjunctiva, the investigators noted.

“We speculate that the virus may diffuse in the fluid of the tears from lacrimal glands because of systemic viremia, as has been demonstrated for HIV,” the researchers wrote in their paper. “Among the theories described herein, direct contagion from airborne droplets seems to be the most likely theory.”

Additionally, the study authors observed a low rate of ocular signs and symptoms in patients who tested positive with the conjunctival swabs.

Considering the study’s findings, the slightly invasive conjunctival swab may be considered as a supplementary diagnostic test for COVID-19, they suggested.