Glaucoma test provides potential pathway for Covid-19

A common eye test, conducted hundreds of times at eye clinics daily, could be sending tear droplets up to a meter away from the patient, potentially helping to spread the Sars-CoV-2 virus.

In June 2020, Victoria Hospital, following pioneering research in China, confirmed that the viral RNA of the virus can spread through tears.

Now, researchers in the city have found that a tonometer test, which ophthamologists described as the most common test to check for glaucoma, can eject tear drops into the air to transmit the virus from infected people.

The finding has implications for test subjects infected with Covid-19 or other pathogens, said Prof Saptarshi Basu of the Indian Institute of Science (IISc), an author of the study, which was published in Physics of Fluids, the journal of the American Institute of Physics.

Ophthalmologists use a tonometer to measure eye pressure, which indicates the risk of developing glaucoma.

The instrument works by emitting a puff of air that hits the surface of the eye. Researchers modeled the eye’s response to this puff and took high speed images of eyes undergoing the procedure at Narayana Nethralaya hospital in the city.

When the air puff hits the eye, researchers found that a film of tears on the surface expands into a sheet that spills out over the eyelids. “The cornea is like an elastic surface. So, as it deforms and as it recovers its shape, it gives the eye an additional kick,” Dr Basu said.

“A capillary wave merged with this corneal deflection gives rise to a consolidated wave, and that is what makes the tear fluid expand and go out.”

The waves moving within the eye and tear liquid eventually become unstable, and the tears break up into droplets. The team tracked the speed of those droplets and predicted they could travel up to a meter away from the patient - depending on air flow within the room. “So, what you think is a safe, non-contact procedure, actually carries some risk,” Dr Basu said.

Abhijit Sinha Roy, head of imaging and biomechanics research at the Narayana Nethralaya, said that the research was influenced by a desire to determine how far fluids from the eye could be dispersed by glaucoma testing. Scientists recommend not using eye drops before a glaucoma test unless medically necessary.

At Dr Agarwal’s Eye Hospital, opthamologist Dr Bindiya Hapani, speaking in an independent capacity, said that no infections through tear droplets have been recorded from glaucoma test subjects at the hospital.

“But that is only because we have a strict screening process. Anyone found to have symptoms of the disease are tested in a separate room. Every day, I see 30 to 40 patients - nearly all of whom require a tonometry test,” she said.

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