Coronavirus can spread through the eyes—just as it does through the mouth or nose. When someone who has coronavirus coughs, sneezes, or talks, virus particles can spray from the mouth or nose onto your face. You are likely to breathe these tiny droplets in through your mouth or nose. But the droplets can also enter your body through your eyes. You can also become infected by touching your eyes after touching something that has the virus on it.
ACE2
The virus that led to the 2003 SARS outbreak entered the body through an enzyme called angiotensin converting enzyme 2 (ACE2). Research has found that the virus that causes COVID-19 also likely does the same.
ACE2 is widely found in places throughout the body, including the heart, kidney, intestines, and lungs. ACE2 has also been detected in the human retina and the thin tissue that lines your eye. The virus enters human cells by tricking cells into thinking that it’s ACE2. The virus can attach to a cell at a particular spot, called a receptor, whereACE2 fits exactly. The virus mimics the shape of the ACE2 enzyme well enough that the cell allows the virus to enter it, same as it would the enzyme. Once in the cell, the virus is protected and can replicate until it ruptures the cell. Copies of the virus find new cells to invade, repeating the process.
ACE-2 is a cellular receptor for SARS-CoV-2 and the same receptor also found on conjunctival and choroid epithelia, the aqueous humour, retina, conjunctiva and cornea.
The binding capability of ACE2 protein on conjunctival epithelial cells to SARS-CoV spike protein is much lower than that in lung tissues.
Coronavirus and Conjunctivitis
Viral conjunctivitis is known to present with upper respiratory infections (colds, flus, etc.) and may be a symptom of the COVID-19 virus. Eye symptoms occurred in the middle stages of infection.
Increasing evidence also suggests that up to 3% of COVID-19 patients can present conjunctivitis. In comparison, 83% to 99 % of people develop a fever and 59% to 82 % of people experience a cough. Symptoms range from conjunctival hyperemia, hypersecretion, chemosis, to epiphora, ocular secretions.
Conjunctivitis is an inflammation of the membrane covering the inside of the eyelids and the white part of the eye (sclera). It is often referred to as pink eye. The three most common eye symptoms experienced by people with a confirmed diagnosis of COVID-19 were photophobia, or light sensitivity (18%), sore eyes (16%) and itchy eyes (17%). In 80% of the participants, the eye symptoms lasted less than two weeks. All three of these eye symptoms are commonly associated with the conjunctivitis.
Pink eye, also known as conjunctivitis, is an inflammation of the clear tissue over the whites of your eyes and the inside of your eyelids. It usually leads to redness and swelling of the eyes. A viral or bacterial infection can cause it. Only 0.7 percent of people with mild symptoms developed pink eye, while it occurred in 3 percent of people with severe symptoms.
Chemosis is a swelling of the thin membrane that covers the eye. Chemosis can be a symptom of pink eye or a general sign of eye irritation. Epiphora (excessive tearing) may present as the first symptom of COVID-19.
Ocular Tropism of Respiratory Viruses
Respiratory infection transmission via the eye and lacrimal-nasal pathway elucidated during the 1918 influenza pandemic, remains to be explored in this crisis. Respiratory viruses (including adenovirus, influenza virus, respiratory syncytial virus, coronavirus, and rhinovirus) cause a broad spectrum of disease in humans, ranging from mild influenza-like symptoms to acute respiratory failure. While species D adenoviruses and subtype H7 influenza viruses are known to possess an ocular tropism, documented human ocular disease has been reported following infection with all principal respiratory viruses.
In this review, we describe the anatomical proximity and cellular receptor distribution between ocular and respiratory tissues. All major respiratory viruses and their association with human ocular disease are discussed. Research utilizing in vitro and in vivo models to study the ability of respiratory viruses to use the eye as a portal of entry as well as a primary site of virus replication is highlighted. Identification of shared receptor-binding preferences, host responses, and laboratory modeling protocols among these viruses provides a needed bridge between clinical and laboratory studies of virus tropism.
Respiratory viruses are typically spread by inhalation of virus-containing aerosols expelled by infected inpiduals or by direct or indirect contact with virus-contaminated fomites on environmental surfaces. However, the epithelia of the human eye represent an additional mucosal surface which is similarly exposed to infectious aerosols and contaminated fomites.
Viruses which are generally considered respiratory pathogens are nonetheless capable of causing ocular complications in infected inpiduals and establishing a respiratory infection following ocular exposure.
There are several properties which permit the eye to serve as both a potential site of virus replication as well as a gateway for transfer of virus to extraocular sites to establish a respiratory infection. This is achieved primarily by the nasolacrimal system, which provides an anatomical bridge between ocular and respiratory tissues.
The lacrimal duct collects tear fluid from the ocular surface and transports it to the inferior meatus of the nose, facilitating the drainage of virus from ocular to respiratory tract tissues in a replication-independent manner, thus serving as a conduit for virus-containing fluid exchange between these sites.
When placed on the eye, fluid can be taken up by the conjunctiva, sclera, or cornea, but the majority of liquid is drained into the nasopharyngeal space or swallowed; absorption of tear fluid
Human adenoviruses, are nonenveloped, double-stranded DNA viruses with over 50 known serotypes pided into at least six subgroups. Adenoviruses are most commonly associated with respiratory illness in humans, ranging from mild to acute respiratory disease, but are capable of causing a perse range of clinical symptoms depending on the serotype, including gastroenteritis and ocular disease, with or without respiratory involvement.
Species D adenoviruses exhibit an ocular tropism. Human disease with species D adenoviruses, notably of serotypes 8, 19, and 37, has frequently been associated with epidemic keratoconjunctivitis a highly contagious and severe ocular disease, which can progress to hemorrhagic conjunctivitis. Ocular disease has been documented following human infection with over half of all identified adenovirus serotypes.
The great majority of human infections with avian and human influenza A viruses result in respiratory disease, but additional symptoms (including ocular and gastrointestinal complications) have been documented. Notably, >80% of all human infections with Seasonal influenza subtype H7 viruses have presented with conjunctivitis.
Human coronaviruses (HCoVs) generally cause mild upper respiratory tract infections in humans. Among coronaviruses which have circulated in the human population, two were identified in the 1960s (HCoV-229E and HCoV-OC43), and two others (HCoV-HKU1 and HCoV-NL63) were identified recently. Similar to other human respiratory coronaviruses, HCoV-NL63 typically causes both upper and lower respiratory tract infections, notably in young children and immunocompromised adults, but conjunctivitis has been reported in select cases.
An association between HCoV-NL63 infection and Kawasaki disease (a systemic vasculitis of childhood for which presentation with bilateral conjunctivitis is one criterion for diagnosis) has been reported.
In contrast to other human coronaviruses, SARS-associated coronavirus, first identified in 2003, is a viral pneumonia capable of rapid progression to severe disease and death. Eye or mucous membrane exposure to body fluids and a lack of wearing eye protection were both associated with an increased risk of SARS coronavirus transmission from infected patients to health care workers during the 2003 SARS outbreak, demonstrating the potential for virus transmission following exposure of unprotected eyes to this respiratory pathogen
Currently, our understanding of the possible ocular involvement in SARS-CoV-2 infection is very limited and gradually expanding.
Nevertheless, the fact that the ocular manifestation could be the first presenting feature of the novel coronavirus pneumonia should not be neglected by the general population, health professionals as well as policymakers and teams.
How to Protect Your Eyes
Wash your hands often and stay home whenever you can. If you go out, keep 6 feet away from others and wear a mask. Continue to practice safe hygiene habits for wearing and caring for them. Wash your hands before putting them in, or taking them out.
Wear glasses, your glasses lenses may help protect your eyes from any respiratory droplets. In addition to the small amount of protection offered by glasses, eyeglass-wearers tend to touch their eyes far less frequently. If you don’t wear glasses, try sunglasses. And if you’re caring for someone ill try safety glasses or goggles.
Don’t rub your eyes. It can be a hard habit to break. Moistening drops may help ease itchiness. Wash your hands for 20 seconds before and after you do it. If you must touch your eyes, use a tissue instead of your fingers.
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