The coronavirus may cause "significant" eye abnormalities in severe cases, research suggests.
The infection is thought to be mild in four out of five cases, however, it can trigger a disease called COVID-19.
The coronavirus' effect on a patient's eyes was first brought to light when Dominic Cummings claimed the 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 during the UK's first lockdown.
While experts were on the fence at the time, research has since suggested the coronavirus can enter the eyes, with children in particular experiencing related symptoms. Getting behind the wheel of a car, however, is not advised if your eyesight may be impaired.
In the latest development, scientists from the French Society of Neuroradiology used MRI scans to identify any eye abnormalities in 129 people with a severe bout of the infection.
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Just under one in 10 (7%) had some irregularity to at least one of their eyeballs, namely nodules at the back of the organ. The scientists are investigating whether this will have a lasting impact on the patients' vision.
Although unclear why this may be occurring, the coronavirus could trigger an immune response that leads to damaging inflammation throughout the body.
The coronavirus was initially considered a respiratory infection, however, it is now known to affect many parts of the body.
The NHS states the main signs of infection are a fever, cough, or loss of taste or smell.
This list has been accused of being too limited, with the World Health Organization (WHO) stating conjunctivitis – or pink eye – is a "less common" coronavirus symptom.
Eye abnormalities have shown up on coronavirus patient MRI scans, however, research supporting this was fairly limited.
To learn more, the French scientists studied 129 people with severe COVID-19, all of whom had a brain MRI.
Results – published in the journal Radiology – reveal nine of these individuals had one or more nodules at the back of their eyeball, which is responsible for central vision.
Eight of the patients had nodules in both eyes.
"We showed a few patients with severe COVID-19 from the French COVID-19 cohort had one or several nodules of the posterior pole of the globe," said lead author Dr Augustin Lecler.
"This is the first time these findings have been described using MRI."
The scientists believe patients with severe COVID-19 should undergo routine eye screenings to detect any nodules.
Eight of the nine individuals were treated in intensive care for their coronavirus complications. The scientists worry eye problems may be missed in such critically-ill patients due to life-threatening issues taking priority.
"Our study advocates for screening of all patients hospitalised in the ICU [intensive care unit] for severe COVID-19," said Dr Lecler.
"We believe those patients should receive specific eye-protective treatments."
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Immune-related inflammation may be to blame for the nodules' onset.
Alternatively, the eyes may not drain sufficiently well when a patient is in intensive care, particularly if they are intubated or placed in the prone position.
The prone position involves lying a patient on their front to improve the distribution and volume of air in the lungs. The method has been widely used since early in the coronavirus outbreak.
Seven of the nine patients were in the prone position in intensive care for "an extended time".
Statistics have repeatedly flagged people with underlying medical conditions are at a greater risk of coronavirus complications. Of the nine patients, two had diabetes, six were obese and two had high blood pressure.
Read more: Hand sanitiser causing severe eye injuries
The scientists are following the nine patients to uncover if they have any vision loss as a result of their nodules.
The team is also investigating whether the same issue is arising in milder coronavirus cases.
"We have launched a prospective study with dedicated high-resolution MR images for exploring the eye and orbit in patients with light to moderate COVID," said Dr Lecler.
"Therefore, we will be able to know whether our findings were specific to severe COVID patients or not."
Watch: What is long COVID?