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Study examines ocular transmission of COVID-19

Researchers investigating links between COVID-19 and the eye have found there is a low risk of transmission via tears, after other studies established a link between the virus and conjunctivitis.

In a new study published last week in Ophthalmology, the journal of the American Academy of Ophthalmology (AAO), scientists from the National University Hospital (NUH) in Singapore said there was uncertainty surrounding ocular transmission of COVID-19.

Lead author Dr Ivan Seah, from NUH, worked with colleagues at the National Centre for Infectious Diseases and Dr Rupesh Agrawal, from Tan Tock Seng Hospital, to assess the viral shedding and infectivity of tears in coronavirus disease in 64 tear samples collected from 17 infected patients between day three to day 20 from initial symptoms.

Neither viral culture nor reverse transcription polymerase chain reaction detected the virus, suggesting a low risk of ocular transmission.

Seah also took samples from the back of the nose and throat of patients enrolled in the study. While their tears were clear of virus, their noses and throats were said to be teeming with COVID-19.

However, the research team noted one important caveat: none of the patients in the study had conjunctivitis.

Health officials believe conjunctivitis develops in 1-3% of people with coronavirus. The AAO has also highlighted two recent studies in Journal of Medical Virology and New England Journal of Medicine that suggest the virus can cause conjunctivitis, meaning transmission by aerosol contact with the conjunctiva could be possible.

Seah concluded that his team’s findings, coupled with the low incidence of conjunctivitis among infected patients, suggest that the risk of virus transmission through tears is low.

He hopes their work will guide more research into preventing virus transmission through more significant routes, such as droplets and faecal-oral spread.