Eyes a key frontier in keeping Covid-19 at bay — but there's a downside
Good eye protection has probably been under-appreciated in preventing Covid-19 infections, according to a recent paper published in the UK.
The paper, published in The Lancet, says that most infections are presumed to be from inhalation or from people touching mucosal surfaces with contaminated hands, but evidence from the 1918 influenza pandemic shows that eyes are also an important route of infection.
“Ocular surface droplet deposition is greatly under-appreciated as a probable, frequent route for SARS-CoV-2 transmission,” says the paper, which draws on a number of studies carried out since the latest pandemic began, in March 2020.
One involving public health-care workers in Chennai, India, showed that 19% were infected despite wearing three-layered masks, gloves and shoe covers and using hand sanitiser. However, when they were issued with face shields, infections dropped to zero.
A study in China showed that simply wearing spectacles for eight hours a day sharply reduced the risk of being infected with Covid-19.
Ken Boffard, professor of trauma surgery at Netcare’s Milpark Hospital in Johannesburg, said the British study is “totally credible because you have the tear duct which goes down into the lateral duct”.
It is accepted that inhalation is the primary means of transmission, but there is strong evidence that eye protection offers about 20% more protection against the virus.
“Eighty percent of your Covid protection comes from a mask,” said Boffard. “But it can be passed on through any other moisture-laden surface that isn’t waterproof, such as your eyes. If it goes into the eyes and then down the tear duct, that’s a very valid point of transmission.”
Professor Barry Schoub, chair of the ministerial advisory committee on Covid-19 vaccines, said it is not surprising the eyes are a route of infection if virus-laden droplets land on their mucous membranes.
“The eyes communicate with the nasopharynx [connecting nose to mouth], which is the main site where the virus replicates as it enters into the body,” he said.
The study carried out in China in 2020 confirmed that eye protection is a key part of personal protective equipment, he said. “I think it shows that even guys wearing spectacles were more protected than those that didn’t wear spectacles.”
Schoub noted, however, that transmission through the eyes was secondary to inhalation.
“In the eyes, you’d probably have quite a lot of dilution effect so I can’t imagine it would be nearly as effective a route of transmission as inhalation. With inhalation it goes directly onto the target.”
Dr Kgaogelo Legodi, chair of the specialists’ group at the South African Medical Association, said the logic behind the Lancet paper is “fair”.
“We are dealing with Covid, which is a viral disease,” he said.
Although there is currently no available data on how many people might have been infected via ocular transmission, Legodi follows strict protocols when examining patients.
“I wear a face mask and there is also a screen between me and the patient,” he said.
Legodi said wearing spectacles, sunglasses or a visor would certainly offer the wearer some protection from Covid-19.
Emergency workers such as paramedics have long used eye protection in their work, and not only to guard against contracting TB and Covid-19, said Netcare 911 spokesperson Shawn Herbst.
“There is a lot of stuff like traumatic cases where the patient might be HIV-positive. Hepatitis is another problem that worries us,” he said.
Paramedics generally wear safety goggles when dealing with patients, but the pandemic has made people much more cautious, he said.
Many medics — especially those doing resuscitations — wear “spoggles”, which are plastic safety glasses that form a seal and are held on by a head strap. But they tend to steam up.
“When you’re working with needles and drips, it becomes a problem if you can’t see what you’re doing — you pose a risk to yourself and to the patient,” said Herbst.