Summary
Human coronaviruses bind to specific receptors on host cells. Binding of SARS‐CoV‐2 and SARS‐CoV to ACE2 is required for initiation of infection. There is some preliminary evidence for ACE2 expression on corneal and conjunctival cells, but most of the other receptors known to bind to coronaviruses appear to be found only on fibroblasts and dendritic cells that are found under the surface epithelial layers of the ocular surface. Lactoferrin in tears can inhibit coronavirus binding, as may decoy receptors such as 9‐O‐acetylated sialic acid on tear glycoproteins. Animal studies on human coronaviruses have not focused on the role of ocular surface binding in the infection process, apart from one study that showed conjunctival infection could lead to mild signs and symptoms of pneumonia, but only transient association of SARS‐CoV‐2 with the conjunctiva. While coronavirus infection is rarely associated with conjunctivitis, there have been occasional findings of conjunctivitis in confirmed COVID‐19 patients. Similarly, coronaviruses have been rarely isolated from tears or conjunctival swabs.

Further research
The expression of coronavirus receptors on ocular surface cells needs further confirmatory investigation. It would also be of interest to examine whether contact lens wear or ocular surface diseases such as dry eye disease are associated with increased expression of these receptors. The ability of tears to inhibit binding of coronaviruses to ocular surface cells is another area for research. This may identify substances that can be translated into new prophylaxis treatments to reduce the spread of coronaviruses in the environment.
Further studies, using animal models, on the role of contamination of the ocular surface on progression of the disease are urgently needed. These studies, as well as further studies with human cases of disease, will also help to definitively identify the virus at the ocular surface. As only one study has been able to grow SARS‐CoV‐2 from ocular swabs and then only reported growth early in the disease and did not attempt to grow viruses from subsequent ocular surface swabs, 53  studies should also then examine whether any ocular surface‐associated viruses are infective. Epidemiological studies and case reports should include analysis of ocular complications during coronavirus infection.