Red eyes, ringing ears, sensitivity to light, hearing impairment: although loss of taste and smell have become well-known sensory symptoms of COVID, increasing research suggests that sight and hearing are also common targets of SARS-COV-2, the virus causes the disease.
More than 10 percent of people who get COVID will develop some type of eye or ear symptoms according to the latest data, and both of these categories are among those complaints that can end up being long-lasting. As researchers work to understand how the virus infiltrates our senses, their results suggest that people may need to expand the range of warning signs in order to get tested. Instead of a fever, cough or changes in taste and smell, the first signs of illness can be irritated eyes, hearing problems or impaired balance.
Nearly two years after the pandemic, research into the effects of COVID on the eyes and ears suggests that scientists have much more to learn about how the virus affects our bodies and nervous systems, experts say. “The data is growing and suggesting that this infection has more neuronal consequences than we originally thought,” says Lee Gehrke, molecular biologist at the Massachusetts Institute of Technology.
The eyes have it
One of the first people to try to warn the world about COVID was Li Wenliang, a Chinese ophthalmologist in Wuhan. He likely caught the virus from an asymptomatic glaucoma patient, according to Bhupendra Patel of the University of Utah’s John A. Moran Eye Center, who co-authored a 2021 review of research into the eye symptoms of COVID. Li died of his illness in early 2020, but his case wasn’t the only early indication that eyes could play a role in the spread of the virus. From the start of the pandemic, reports included red eyes as a common symptom.
This wasn’t surprising to scientists. During the 2003 SARS outbreak, researchers in Singapore discovered the virus that causes the disease in patients’ tears. And in Toronto, the risk of infection was higher for health care workers who did not wear eye protection. But because COVID causes severe breathing problems and other symptoms, and because most ophthalmologists closed their offices during the lockdown, the eyes were initially overlooked, Patel says.
For the first year and a half of the pandemic, data collected has shown that around 11 percent of people with COVID develop some type of eye problem, according to a review of multiple studies. The most common symptom is conjunctivitis, or inflammation of the lining of the eyes. This condition affected almost 89 percent of people with eye symptoms, researchers in Iran reported in a meta-analysis from 2021 that included 8,219 COVID patients in 38 studies.
Other eye symptoms can include dry eyes, redness, itching, blurred vision, sensitivity to light, and a feeling that there is a foreign object in the eye. People on ventilators often develop a type of eye irritation called chemosis, which is a swelling or bulging of the membranes of the eyes and eyelids, says Patel. He suspects that up to a third of people with COVID have some type of eye problem – even if it’s just red eyes that don’t bother them. And some eye problems are not visible. Patel and colleagues are working on an unpublished study that he says will be among the first to report that the virus can cause inflammation in the tissue behind the eyeball.
Eye symptoms can appear early or late in the disease, adds Shahzad Mian, an ophthalmologist at the University of Michigan. He and his colleagues reported eye signs and symptoms in nearly 10 percent of 400 patients hospitalized in Michigan in March and April 2020.
A person with COVID can shed the virus through tears, sometimes long after they’ve recovered from the illness. An early COVID patient was a 65-year-old woman who traveled from Wuhan to Italy in January 2020 and was soon hospitalized with a cough, sore throat and conjunctivitis in both eyes. Although their eyes were better 20 days after they were taken, researchers detected viral RNA in eye swabs on day 27. In Lombardy, Italy, researchers found SARS-CoV-2 on the surface of the eyes in 52 of 91 cases of patients hospitalized with COVID in spring 2020, sometimes even with a negative nasal swab.
Studies suggest that the virus may also get into the body through the eyes – either through eye rubbing and direct transmission of tears, or through breath droplets that accidentally land on the eye. When drops containing SARS-CoV-2 were instilled in the eyes of rhesus monkeys in a study in 2020, the animals became ill. A monkey intervention study can’t show if or how often people get infected through the eyes in real life, but the virus appears to multiply in the eye tissue and then get into the nasal passages, Mian says. Eye involvement “can be a portal to COVID rather than just a symptom,” he says.
Up to 6 percent of people will show symptoms in their eyes before other signs of COVID appear, Mian says. Red eyes or irritation can be a sign that someone has the disease, especially if exposure or other symptoms are known. “As a parent, patient, or community member, you should be aware that if you have conjunctivitis these days, you want to make sure it’s not COVID,” he says.
In the ears
Changes in hearing and balance can also be signs of SARS-CoV-2 infection, says Zahra Jafari, an audiologist and cognitive neuroscience at the University of Lethbridge in Alberta. In a meta-analysis from 2021, she and her colleagues found dizziness or dizziness in 12 percent of COVID patients, a ringing in the ear known as tinnitus in 4.5 percent, and hearing loss in 3 percent. One hypothesis of how SARS-CoV-2 could affect the ears is that inflammation caused by the virus can directly affect the hearing system. The virus could also penetrate a barrier between the bloodstream and the inner ear.
Confirming these mechanisms has been difficult because the inner ear is notoriously difficult to examine, says Gehrke. Wrapped in bones and deep inside the head, it’s inaccessible, and animal models don’t always help. Mice are not natural hosts for RNA viruses, so the lab rodents commonly used as replacements for SARS-CoV-2 infection do not work very well.
To study what could happen in the ears of people with COVID, Gehrke teamed up with researchers from several other laboratories to grow human ear tissue using stem cells. Using these tissues, the team was then able to show that two types of inner ear cells have the genes to make proteins – including ACE-2 receptors – that allow SARS-CoV-2 to enter the cells.
Hair cells, which are important for both hearing and balance, can also be infected with the virus, the researchers reported in nature in October. The team was able to confirm that an inner ear infection with the virus is possible by examining human tissue that was removed during surgery planned to treat other conditions. The results “strongly suggest that SARS-CoV-2 patients could actually have hearing loss related to a viral infection due to an infection of the hair cells,” says Gehrke.
Most of the time, both eye and ear symptoms improve on their own, experts say. However, research suggests that in either case, COVID-induced symptoms can linger for a long time. Patel knows two cases where COVID patients have lost the sensation in their corneas, which can cause those corneas to collapse even with minor trauma. This breakdown can lead to corneal infections, damage, and ultimately blindness. Several case reports include ear-related symptoms that persist even after the disease has recovered, Jafari says.
Although visual and hearing impairment still seem less common than loss of smell and taste – which can affect 40 percent or more of people with COVID – studies of the eyes and ears provide insight into the many, and often still mysterious, possibilities that that Virus can go to work in the human body, experts say.
Research also shows how closely our sense organs are intertwined. Nasal passages meet Eustachian tubes and eyeballs. “The nerves that allow you to taste, the nerves that allow you to smell, and the nerves that allow you to feel the cornea – all of these are part of the central nervous system where the brain is connected to these different parts” says Patel. Seeing, smelling and tasting – “these are all interconnected.”