COVID-19, the infectious viral ailment triggered by the SARS-CoV-2 strain of the novel coronavirus, is known to primarily affect the upper respiratory tract and give rise to cough, fever, sore throat. However, a few COVID positive patients have also reported symptoms presenting in other organs of the body, including the eyes in the form of conjunctivitis.
How And Why Does COVID-19 Instigate Conjunctivitis?
The causative pathogenic microorganism of COVID-19 – SARS-CoV-2, which is a novel strain of coronavirus, enters the human host via specific routes mediated by certain externally expressed cellular proteins, similar to disease transmission in other viral diseases of SARS (Severe Acute Respiratory Syndrome) caused by SARS-CoV strain of coronavirus and MERS (Middle East Respiratory Syndrome) triggered by MERS-CoV type of coronavirus. These specialised proteins are termed cell surface receptors, with one particular compound – ACE2 or Angiotensin-Converting Enzyme II being a binding site for the spike protein of SARS-CoV-2. This protein is present on the external boundaries of epithelial cells in the skin, nasal passage, oral cavity of the mouth and tongue, throat, lungs, thereby justifying the major symptoms of COVID-19 afflicting the upper respiratory tract.
Additionally, ACE-2 protein is also expressed in the epithelium/outer layer of tissues in the intestines, kidneys and the eyes, although in comparatively smaller concentrations in the cornea, conjunctiva of the latter. Thus, when spike proteins in SARS-CoV-2 bind to the ACE-2 receptors in the eyes, it causes redness and inflammation in the conjunctiva – the outer tissue layer covering the front portion, resulting in conjunctivitis, otherwise known as pink eye. From here, the viral vector can spread via the nasolacrimal system into the nose, throat, oral cavity and lungs, triggering more serious COVID-19 infection.
Nevertheless, the number of coronavirus positive patients who display conjunctivitis as a symptom are very few. Healthcare professionals, medical experts and scientific researchers attribute this to a specific protective protein in tears known as lactoferrin. The exact biological cellular mechanism involved in the viral transmission of COVID-19 via the eyes is this. SARS-CoV-2, prior to attaching to ACE-2 receptors, initially binds to heparan sulphate, yet another cell surface receptor that is present ubiquitously in ocular tissues of the cornea and conjunctiva. Only when these bonds are firm can the viral vector link firmly with ACE-2 proteins and inflict disease in the human host. Lactoferrin, a protein secreted in large amounts by the tear glands in the eyes, does not permit the binding of SARS-CoV-2 spike protein with heparan sulphate, thereby stopping subsequent bonding with ACE-2 and averting COVID-19 infection.
Are There Any Precautions To Safeguard The Eyes?
However, since the COVID-19 pandemic is still ravaging in many countries around the world despite the successful invention of preventive vaccines and the launch of large-scale inoculation drives, the best way to stay safe and disease-free is by following simple safety precautions to avoid contracting COVID-19.
Besides wearing face masks, maintaining social distancing in public places and frequently sanitizing hands after touching surfaces like doors, windows, tables that many people have already come in contact with, some simple tips help to protect the eyes – the vital delicate sensory organs that enable the sense of sight.
- Wearing protective glasses or face shields that cover the eyes, when encountering many people at work or while travelling.
- Thoroughly cleaning contact lenses before use and storing them in clean cases, replacing lens solution regularly.
- Steering clear of rubbing the eyes often, especially after touching surfaces like tables, chairs at work, in restaurants, public places, that have been used by many people before.