So far, research shows SARS-CoV-2 (COVID-19) is transmitted through person-to-person contact, airborne droplets or contact with contaminated surfaces. It binds to angiotensin converting enzyme-2 (ACE2) to spread infection in humans.

Thus, researchers speculate the ocular surface may serve as a potential infection site for COVID-19. However, a new comprehensive review shows coronaviruses are unlikely to bind to ocular surface cells to initiate infection. The researchers also report a small chance the virus can travel from the nasopharynx or through the conjunctival capillaries to the ocular surface.

The team consisted of optometric experts Mark Willcox, DSc, director of research at the School of Optometry and Vision Science at UNSW (Sydney), Karen Walsh, MCOptom, professional education team leader and clinical scientist at the Centre for Ocular Research & Education (CORE) at the University of Waterloo, Jason Nichols, OD, associate vice president for research and professor at the University of Alabama at Birmingham School of Optometry, Philip Morgan, PhD, director of Eurolens Research at the University of Manchester, and Lyndon Jones, DSc, director of CORE.

The investigators conducted a literature search on April 15, yielding 287 relevant publications. In reviewing the current literature, they found preliminary evidence of ACE2 expression on corneal and conjunctival cells but noted that most of the other receptors to which coronaviruses bind are located under the epithelia of the ocular surface.

Furthermore, the investigators added that coronaviruses are rarely associated with conjunctivitis and vice versa, with only occasional cases reported in patients with COVID-19. They noted that coronaviruses have rarely been isolated from tears or conjunctival swabs.

“Necessary precautions to prevent person-to-person transmission should be employed in clinical practice throughout the pandemic, and patients should be reminded to maintain good hygiene practices,” the study authors concluded in their paper.

Willcox MDP, Walsh K, Nichols JJ, et al. The ocular surface, coronaviruses and COVID-19. Clin Exp Optom. May 13, 2020. [Epub ahead of print].