Covid-19 / Medicine

Diagnosing Covid-19 in Tears

A new study may seek to replace nasal swabs to diagnose coronavirus

Image by LhcCoutinho from Pixabay

Testing remains at the forefront in the fight against Covid-19.

Several pressures from politics to reliability and availability of of tests in the US have hampered the effort to test people for Covid-19. Early on, the roll out of testing in the US was criticized by many as experts as too slow to address the rise in cases. Even to date, the US falls short of the level of testing that many experts feel is needed to begin to contain the virus.

Beyond political pressures, Covid-19 tests themselves have come under scrutiny for failing to provide reliable results. Tests that detect antibodies against SARS-Cov-2 have shown limitations in reliability, and may provide people with a false sense of security. Even with these limitations, testing is still one of the most critical public health efforts in containing an outbreak. Researchers are continuing efforts to develop convenient and reliable tests for Covid-19.

By now, most people have seen images of current Covid-19 tests. Social media has been inundated with videos of people succumbing to the insertion of a long nasal swab into their nose. This swab is intended to go deep beyond the nasal cavity into the nasal pharynx, where respiratory viruses can be detected. These images, and people’s reactions to their own testing have left people with the impression that Covid-19 testing is uncomfortable at best, and painful at worst.

Public appetite and demand from the scientific community for reliable and convenient Covid-19 tests has pushed some researchers to look elsewhere in the body to detect the virus. Researchers at the University of Minnesota Medical School have turned their attention to the eyes, and in particular the tears to test for the virus. A team, lead by Opthalmologist Dr. Hossein Nazari have launched a study looking into using human tears as a possible test for Covid-19.

Why test tears for Covid-19?

Tears, produced by lacrimal glands deep within the eye socket, have a close anatomical relationship to the nasal cavity. Anyone who has shed tears in the time if sadness knows how quickly a runny nose follows tears. In fact, there is a physical structure that connects the tissue that lines the eye socket — called the conjunctiva — to the nasal cavity that allows for drainage of tears. Dr. Nazari’s team is investigating the idea that viruses can permeate the conjunctiva and be detected there. Their test would pull tears form the inner corner of the eye into a a microcapillary tube through capillary motion and use them to analyze for presence of SARS-CoV-2.

The test would rely on a technique commonly used in biomedical laboritories called real-time polymerase chain reaction or RT-PCR. This assay uses synthetic primers to amplify segments of the SARS-CoV-2 genome, which can be detected in real time to determine the presence and quantity of viral load in the body. RT-PCR assays have some documented shortcomings, but remains one of the most reliable techniques for detecting the presence of viral genetic material.

Due to the proximity of the conjunctiva to the nasal respiratory mucosa, one of the primary locations of infection in Covid-19, the tears may be a reliable and easy area to test for the virus. In fact, one study looking at SARS-CoV-2 infection was able to detect the virus in patients who tested positive through nasal swab.

The move to develop more convenient testing seeks not only to keep up with the demand for reliable testing, but to lower the public barrier for testing. Developing an easy and minimally invasive test could lessen public resistance to testing spurred by fear of pain, cost or long waits at testing centers.

Medical student, molecular biologist and educator. I write about science and medicine.

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