Both the World Health Organization and the United States Centers for Disease Control and Prevention (CDC) recommend not touching your face to reduce the risk of getting the SARS-CoV-2 coronavirus. Besides the nose and mouth, the eyes can also be a route of infection. But there are still questions about it. To what extent is this likely to occur? How is it possible to know if someone has been infected through the eyes? Are our tears also contagious? We explain everything we know (and what we don’t) about it.
- Infection through the eyes exists although it is not the main form of infection
- How is the coronavirus transmitted through the eyes?
- Tears are a possible source of contagion
- The risk of catching eye protection is 6% compared to 16% if it is not worn
- Avoid touching your face and washing your hands: other recommendations to prevent infections
- Maldita Clinic: Do you have questions about health-related issues?
Eye infection exists although it is not the main form of infection
Rubén Pascual, ophthalmologist and founder of the Ocularis Project, explains to Damn science what the eyes are a possible route of transmission of SARS-CoV-2. But the ophthalmologist insists that more studies are still needed in this regard. “There is a good consensus that it would be a minor route, much less important than contagion through the nose or mouth. Even taking into account the mask ”, he indicates.
The expert emphasizes that when we breathe we are, on the one hand, expelling aerosols and droplets, and on the other, aspirating and introducing the particles, drops, and aerosols around us. The ocular surface does not work like this: “It does not ‘spray’ the tear film through the air, nor does it have an ‘aspirator’ that draws in the air from the environment”.
Karen Walsh, a scientist at the Center for Eye Research and Education (CORE) at the University of Waterloo (Canada), tells Damn science that exist several studies with different conclusions that analyze whether the coronavirus can be transmitted through the eyes. Some like this or this indicate that it is possible. Others like this, this or this point out that it is unlikely to occur but that cases may occur and recommend eye protection to avoid infections in this way in healthcare personnel.
How is the coronavirus transmitted through the eyes?
Pascual explains that the ocular surface, especially the conjunctiva (a thin membrane that covers the inner surface of the eyelid and the white part of the eyeball), has similarities to the inner surface of the respiratory system. According to his account, the mucous membranes of the nose, mouth, and throat resemble the conjunctiva, so “viruses that settle and reproduce through the respiratory tract can sometimes remain viable on the surface of the eye”.
“As the tear circulates and drains into the nostrils, theoretically a sufficient amount of viable virus (that has come from outside) in the tear film can reach the mucosa of the nose and cause infection,” he indicates. Walsh points out that more studies are still needed to know for sure what exactly happens if a person has been infected through the eyes.
But, Can you tell if a person has been infected through the eyes? “It is not possible to know. If it is first infected through the conjunctiva, the virus passes into the nose before there are symptoms of COVID-19 ”, answers Pascual.
Tears are a possible source of contagion
For his part, professor and doctor of ophthalmology Jorge Alió explain to Damn science that some patients, at the beginning of their clinical signs or even before having anything, have presented conjunctivitis that causes them to have irritated eyes, feel discomfort and secrete tears.
These tears, he indicates, can be carriers of the virus. There are studies like this, this or this in which the RNA of the virus or viral load has been detected in the eyes or tears of patients.
If there is enough viral load in the tears, someone infected could pass the virus to other people “Either because he touches them with his hands or with a handkerchief or object with which he touches his face or because someone touches his face, for example by putting an eye drop.”
Alió explains that they can be differentiated two stages in conjunctivitis in some patients: an initial one (viral), with positive PCR in the tear, and another that occurs when the patient is seriously ill, generally already in the ICU, in which his eyes are irritated “due to the general inflammatory situation he suffers.” “This second conjunctivitis is not contagious by tears since CRP is negative in the tear“, Add.
The risk of catching eye protection is 6% compared to 16% if it is not worn
Is it advisable to protect the eyes in some way to avoid contagion? From the Galician Delegation of the National College of Optometrists Opticians (CNOO), they point to Damn science what Eye protection is highly recommended. Alió adds that above all it is advisable in environments where contamination is more possible or viral load greater (hospitals or places with many people or with possible infected people).
Face shields and glasses are associated with a lower risk of infection compared to the absence of ocular coverage, according to this review of studies published in the scientific journal The Lancet.
The risk of getting infected when wearing glasses or face protection is 6% compared to 16% if they are not worn, according to 13 studies analyzed (in which 3,713 people participated) and as we already explained here.
Pascual explains that the objective of wearing glasses (either sunglasses or prescription) prevents saliva droplets in the air from reaching the surface of the eye. Although, for him, “it would help more to remember not to touch our eyes (better the face in general), whether we wear glasses or not”.
In fact, the Galician Delegation of the CNOO considers that the ideal would be to use protective glasses that also cover the sides to minimize the possibility of contact with the eyes or protective screens. “These two elements, apart from protecting our eyes from the entry of polluting particles that are in the air, also prevent us from touching our eyes with our hands,” he says.
The Ministry of Health recommends that, upon returning home, Let’s disinfect the objects that we have used on the street. The glasses (both the lenses and the frame) must be cleaned with soap and water to kill the coronavirus and not damage them, as explained by the Center for Eye Research and Education at the University of Waterloo in an infographic with tips for care of the eyes.
Avoid touching your face and washing your hands: other recommendations to prevent infections
As we have already explained, to reduce the risk of contagion it is important to not touch your face and wash your hands with soap and water or an alcohol-based sanitizer. Contact lens wearers have to take extreme care to follow proper hand hygiene before putting them on.
There is no scientific evidence that those who use contact lenses have a higher risk of contracting COVID-19 than those who wear glasses. But, in case they cause us any discomfort that leads us to touch our eyes, it is better to change them for glasses, as we already explained here.