Scientists believe they have found coronavirus particles in the retinas of three people who died with the infection.
Early research suggests the coronavirus is mild in four out of five cases, however, it can trigger a disease called COVID-19.
The coronavirus is primarily considered to be an airway infection. In March 2021, however, Italian medics found more than half (57%) of patients have the virus on the surface of their eyes.
Long COVID, lingering complications after a former coronavirus patient has supposedly overcome the infection, has also been linked to immune cells on the eye.
In the latest development, scientists from the Federal University of São Paulo in Brazil have found "presumed" coronavirus particles in "various layers of the retina" in three cadavers.
Eye abnormalities are not considered to be main symptoms of the coronavirus. Nevertheless, the infection has been linked to conjunctivitis, or "pink eye".
During the UK's first lockdown, Dominic Cummings hit the headlines when he claimed a suspected coronavirus infection affected his vision.
Boris Johnson's former chief adviser used this to justify driving to the beauty spot Barnard Castle to reportedly test his eyesight, amid the "stay at home" restriction.
According to the NHS, the coronavirus' main symptoms are a fever, loss of taste or smell, or a new, continuous cough.
This list has been accused of being too limited, with the eyes also known to be affected by the infection in some cases.
It was unclear whether the coronavirus itself invades the eyes or the infection triggers an inflammatory immune response that impacts vision.
To learn more, the São Paulo scientists analysed two men and one woman who died – between the ages of 69 and 78 – with a confirmed coronavirus infection.
With the permission of the deceased's families, the scientists found "presumed" coronavirus protein particles in the victims' retinas, as reported in the journal JAMA Ophthalmology.
One of these was the so-called spike protein, which the virus uses to enter a person's cells.
The retina contains millions of light-sensitive cells that receive visual information. The retina then sends this information to the brain via the optic nerve, enabling sight.
The scientists have acknowledged their study was small, "caused by difficulty in obtaining the eyes and lack of proven pathogenic viral effect in the retina".
Nevertheless, they have concluded: "The present observations show presumed [coronavirus] particles in various layers of the human retina, suggesting they may be involved in some of the infection’s ocular clinical manifestations".
The team hopes their results will enable others to better understand the course of the coronavirus infection "and may direct some avenues of future research".
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