Researchers in China have found that people who wear glasses are at lower risk of contracting COVID-19. The authors of the study, published in JAMA Ophthalmologynoted that few patients wearing glasses have been admitted to a hospital suffering from COVID-19 since the coronavirus outbreak in Wuhan in December 2019. For further investigation, they collected data on the wearing of glasses from all patients with COVID-19 as part of their medical history.
Their small study found that only 16 (5.8%) of the 276 patients admitted with COVID-19 wore glasses for more than eight hours a day. When they found that all of these patients were nearsighted, they next examined the proportion of people with myopia (nearsightedness) in Hubei Province, where the hospital is located. They found this to be much larger (31.5%), indicating that the proportion of myopic COVID-19 hospital admissions was more than five times lower than expected by this population.
This is a fascinating observation, but as with all individual studies, the results must be treated with caution. While eye protection has always been As an important part of personal protective equipment (PPE), the difference reported in this study raises suspicion. This does not mean that the results may not be real, but that we should not inform about major behavioral changes (e.g. wearing safety glasses next to our face masks) until they have been independently confirmed.
Are eyes a window to the virus?
One of the most important steps for a viral infection is entering the body for the first time. While most of our body is covered with protective skin, which is very effective in preventing viruses or bacteria from entering our body, much thinner "membranes" cover our respiratory tract, digestive system and eyes. The role of these thinner membranes is to let external things like oxygen, food and, in the case of eyes, light into our bodies. Unfortunately, viruses have learned to take advantage of these entry points.
For this reason, PPE was designed to protect these entry points through the use of face masks, goggles, and protective clothing. While we can imagine that the main attack on these regions is from virus particles that are airborne as aerosols, the main route by which virus particles get to these vulnerabilities is actually via our hands. Hence the COVID-19 advice to wash our hands frequently for 20 seconds or more and avoid touching our faces.
So it makes sense to cover our eyes with glasses to provide additional protection, both from the virus, which can be transmitted into other people's breath, and to prevent wearers from touching their eyes. Indeed there in February were reports of people who get COVID-19 by not properly protecting their eyes in healthcare. It is also known that similar entry points into the body (ACE-2 receptors) are preferred by the coronavirus are also present in the eyes.
Should we start wearing protective glasses?
A critical part of interpreting evidence from observational studies is remembering that correlation (two things happen together) does not necessarily imply causality (one causes the other). A controlled trial or test is now required to test for the cause.
Ideally, this would follow two carefully matched groups of people – some wear glasses, others don't – to determine which group is more likely to be infected. The evidence from such a controlled study will always be far stronger than the evidence from an observational study like the one in the most recent publication.
We must also note that the authors of this study listed a number of weaknesses. It was a very small study in one place. The researchers' data for the general population comes from a much earlier study on a sample that did not exactly match (in terms of age, demographics, and other factors) their sample hospitalized with COVID-19. And they couldn't guarantee that all people with myopia in the general population wore glasses for more than eight hours a day.
While this new study is very interesting, there are many reasons to be careful with this finding. We certainly need more data before we can offer advice on wearing safety glasses next to our face masks.