TORONTO -- Pink eye, or conjunctivitis, and other abnormal eye conditions could be a less common symptom of COVID-19 and also a possible source of transmission, according to several recent studies.

The preliminary findings, along with an anecdotal report, prompted the American Academy of Ophthalmology to recommend health-care workers not only protect their mouth and nose with a mask, but also their eyes, by wearing goggles or a shield, when caring for patients who may have COVID-19.

“Existing data suggest that conjunctivitis is an uncommon event as it relates to COVID-19,” the Academy wrote on Friday.

“However, because conjunctivitis is a common condition overall ... it may happen that ophthalmologists are the first providers to evaluate patients possibly infected with COVID-19 … It is possible - but not proven - that a patient with COVID-19 associated conjunctivitis could have infectious virus in their ocular secretions."

The most common symptoms cited by Health Canada, the U.S. Centers for Disease Control, and the World Health Organization are fever, difficulty breathing, dry cough, and tiredness. Other symptoms could also include aches and pains, sore throat, and more rarely, diarrhea, nausea, and runny nose. There is also growing evidence that a sudden loss of smell or taste could be an early sign of COVID-19 infection, particularly for otherwise asymptomatic patients.

Data from 1,099 patients hospitalized throughout China with the novel coronavirus found that 0.8 percent reported “conjunctival congestion”, according to a study published in the New England Journal of Medicine.

Another COVID-19 study involving 38 patients from Hubei province that specifically looked at conditions relating to the eye found that a dozen of them had eye-related symptoms including “conjunctival congestion”. Eight of the 12 patients were considered “severe” or “critical” cases, suggesting that these ocular symptoms were more common in patients with severe pneumonia, the study’s authors wrote.

“Because unprotected eyes were associated with an increased risk of transmission of SARS-CoV-1, in support of our current results, our results might suggest that SARS-CoV-2 might be transmitted through the eye,” the authors wrote. SARS-CoV-2 is the virus that causes COVID-19, and SARS-CoV-1 is the virus behind SARS, which caused dozens of deaths in Canada and hundreds in China and Hong Kong in 2003.

The study published in the Journal of the American Medical Association also found that patients with the eye-related symptoms also had a greater likelihood of having higher white blood cell and neutrophil counts, as well as higher C-reactive protein levels - all indicators of possible infection - than patients without eye-symptoms. High levels of other blood test values including lactate dehydrogenase, which may indicate tissue damage, were also found.

In a statement to Monday, the Canadian Opthalmological Society said it is aware that, in some cases, conjunctivitis has been present as a “first symptom” of COVID-19.

“People should take care to monitor for all signs and symptoms of the virus, get tested if symptoms are present, and continue to physically distance as directed by the PHAC,” a spokesperson said by email.

“The known case emphasises the need for eyecare professionals to remain vigilant in their practice and care of all patients.”

Two other studies that – unlike the others – have yet to be peer-reviewed indicated the virus may be detected in the tears of COVID-19 patients, but suggested that the likelihood of transmission through eye secretions was relatively low.

Red eyes appeared to be a key sign of infection, Chelsey Earnest, a nurse at Life Care Center in Kirkland, Washington told CNN in March, even when other symptoms were not immediately evident. She described it as similar to “allergy eyes”. Life Care was one of the earliest deadly COVID-19 clusters in the United States.

An asymptomatic glaucoma patient was thought to be the source of infection for Li Wenliang, the Chinese ophthalmologist and whistleblower who later died from COVID-19.