SARS-CoV-2, the virus responsible for COVID-19, is primarily known for causing respiratory illness, yet its effects extend throughout the body. Ocular symptoms, including the appearance of red eyes, have been documented in individuals with the disease since the beginning of the pandemic. Recognizing these non-traditional signs is important for understanding the full spectrum of this viral infection.
The Direct Link: Red Eyes as a COVID Symptom
Red eyes are a recognized, though generally uncommon, symptom associated with a SARS-CoV-2 infection. This manifestation is medically identified as viral conjunctivitis, often referred to by the common name of “pink eye.” Conjunctivitis represents an inflammation of the conjunctiva, which is the thin, transparent membrane covering the white part of the eye and the inner surface of the eyelids.
Studies on the prevalence of this ocular symptom have shown a wide range, with reports indicating it affects anywhere from 1% to over 30% of patients diagnosed with COVID-19. The typical presentation involves redness, irritation, a watery discharge, and a gritty sensation, as if a foreign body is present in the eye. This viral condition frequently begins in one eye and may then spread to the other, following the pattern of many other types of viral pink eye. Although it is not the most frequent sign of infection, conjunctivitis can, in some cases, be the initial or sole symptom a person experiences.
How SARS-CoV-2 Affects the Eyes
The ability of SARS-CoV-2 to target the eyes is rooted in the specific cellular structures present on the ocular surface. The virus requires the angiotensin-converting enzyme 2 (ACE2) receptor to gain entry into human cells. These receptors are notably expressed in the epithelial cells of the conjunctiva and, to a lesser extent, the cornea.
The presence of the ACE2 receptor allows the viral spike protein to bind and initiate the process of cellular invasion. This entry is often facilitated by an enzyme called TMPRSS2, which is also expressed in the ocular tissues and helps activate the virus for fusion with the host cell membrane. Once the virus gains a foothold, it replicates and triggers an immune response. This localized inflammatory reaction is what causes the blood vessels in the conjunctiva to dilate, resulting in the characteristic redness and irritation.
Distinguishing Ocular Symptoms from Other Causes
Red eyes are a highly non-specific symptom, meaning they can result from numerous causes, including seasonal allergies, bacterial infections, or other common viral illnesses. Differentiating COVID-related conjunctivitis from these other conditions is a practical concern. A key factor in distinguishing the cause is the presence of other systemic symptoms that accompany the ocular irritation.
COVID-related conjunctivitis is usually seen alongside other signs of a respiratory infection, such as fever, persistent cough, fatigue, or the loss of taste or smell. In contrast, allergic conjunctivitis, which also causes red and watery eyes, is typically characterized by intense itching and almost always affects both eyes simultaneously. Bacterial conjunctivitis often presents with a thick, sticky discharge that can cause the eyelids to crust or stick together. This feature is less common in the clear, watery discharge of a viral infection like COVID-19.
If red eyes develop along with other known symptoms of COVID-19, seeking testing is a sensible course of action. While the red eyes themselves are usually mild and self-limiting, their appearance in conjunction with a fever or respiratory trouble should prompt consideration of the underlying viral infection. This approach allows for appropriate quarantine measures.