The study, published in a preprint format in MedRxiv, found that a certain protein enzyme produced by the eyes called angiotensin-converting enzyme-2, or ACE-2, can serve as a carrier for SARS-CoV-2 to enter the body.
According to the researchers, SARS-CoV-2 latches onto ACE-2 receptors, which are also known as the "gateway" into the body’s cells.
The study was spurred by cases wherein conjunctival signs and symptoms were observed in a subset of patients with COVID-19. The researchers first analyzed 10 post-mortem eyes from people who did not die of the disease, and checked for the presence of ACE-2, as well as TMPRSS2, another enzyme that helps viral entry following binding of the viral spike protein to ACE-2.
According to the researchers, ACE-2 and TMPRSS2 must both be present in the same cell for the virus to successfully replicate. (Related: Coronavirus updates: Global caseload now over 4.2 million, Wuhan orders tests for ALL residents, South Korea battles new cases.)
The two enzymes were found in all of the 10 samples.
The enzymes, the researchers said, were predominantly found in the conjunctiva, or the tissue that lines the inside of the eyelids. The two enzymes were also found in the clear outer layer of the eye, or the cornea, and the border between the cornea and the white of the eye, called the limbus.
As described in their study, once SARS-CoV-2 successfully latches onto the receptors, it becomes much easier for the virus to infect the cells, which would subsequently facilitate their replication.
“Ocular surface cells including conjunctiva are susceptible to infection by SARS-CoV-2, and could, therefore, serve as a portal of entry,” lead researcher Lingli Zhou wrote in their study.
As per the researchers, this means that if droplets from an infected person's sneeze or cough were to land on the surface of the eye, the virus could begin infiltrating cells there.
In addition, Zhou said this finding opens up the possibility that tears may also serve as a way to further spread the infection, noting that aside from being a point of entry into the body, the eyes could also serve as “a reservoir for person-to-person transmission of this virus.”
“Infection of ocular surface cells could lead to the eye as being an important carrier, with ocular virus shedding constituting a significant mechanism for infection of other individuals,” the researchers said, adding that their findings highlight the importance of safety practices in the general community to prevent the further spread of the infection, as well as the need for extra caution among ophthalmologists and other medical practitioners.
The results of the research came about a month after doctors from Italy found that their country’s first confirmed COVID-19 patient had detectable levels of the coronavirus in her eyes, long after the infection had cleared from her nasal cavity.
According to the doctors who attended the patient, they took eye swabs daily, with the doctors noting that the virus lingered in the woman’s eyes for 22 days.
As of this writing, the COVID-19 pandemic, caused by the coronavirus which originated in Wuhan, China, has infected 4,430,000 around the world and killed 298,174.
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