Dear Editor,

The COVID-19 outbreak was first identified in the Hubei province of Wuhan, China, in December 2019. It is caused by SARS-CoV-2. The proposed transmission of SARS-CoV-2 is respiratory droplets < 5 μm in diameter or by indirect or direct human-to-human contact.1 SARS-CoV-2 may also be transmitted through the eyes. The receptor for SARS-CoV-2 is angiotensin-converting enzyme 2 (ACE-2). SARS-CoV-2 replicates at the binding site on the surface of target cells, such as ocular tissues, leading to the cleavage of the ACE-2 receptor, activation of the spike protein, and inflammation in the form of ocular manifestations such as conjunctivitis, anterior uveitis, retinitis, and optic neuritis. SARS-CoV-2 can cause eye manifestation.2 ACE-2 is expressed by conjunctival epithelial cells, and the presence of ACE-2 is significantly elevated in conjunctival cells for patients with conjunctivitis, conjunctival nevi, conjunctival papilloma, conjunctival cysts, and conjunctival polyps’ epithelial cells compared to control subjects.3

It has been reported that ocular surface cells were potential infection sites of SARS-CoV-2. The proteases of ocular surface cells facilitate the binding of SARS-CoV-2 on the viral spike protein to the ACE-2 receptor in the conjunctiva, limbus, and cornea. SARS-CoV-2 might exist in tears since there was an expression of ACE-2 on the transmembrane serine protease 2 (TMPRSS2).4 Another study found that SARS-CoV-2 was present on conjunctiva swabs from two out of 11 (18.2%) patients tested for SARS-CoV-2 via nasopharyngeal swabs. A common symptom was conjunctivitis, and SARS-CoV-2 could be transmitted by aerosol contact with the conjunctiva.5

However, the risk of SARS-CoV-2 transmission through tears was low. In a study of 17 patients, none of the 32 patient tear samples was positive for SARS-CoV-2.6 The replication of SARS-CoV-2 was much more efficient than that of SARS-CoV in human conjunctiva and the upper respiratory airways. Thus, eyes could be a potential route of SARS-CoV-2 transmission.7

All of the above information demonstrates that SARS-CoV-2 might be acquired through the eyes, wearing a face shield could benefit, especially during aerosol-generating procedures.

references

1. 1. Peng PW, Ho PL, Hota SS. Outbreak of a new coronavirus: what anaesthetists should know. Br J Anaesth 2020 May;124(5):497-501.
2. 2. Seah I, Agrawal R. Can the coronavirus disease 2019 (COVID-19) affect the eyes? A review of coronaviruses and ocular implications in humans and animals. Ocul Immunol Inflamm 2020 Apr;28(3):391-395.
3. 3. Li S, Li D, Fang J, Liu Q, Sun X, Xu G, et al. COVID-19 receptor ACE2 is expressed in human conjunctival tissue, especially in diseased conjunctival tissue. MedRxiv 2020.
4. 4. Zhou L, Xu Z, Castiglione GM, Soiberman US, Eberhart CG, Duh EJ. ACE2 and TMPRSS2 are expressed on the human ocular surface, suggesting susceptibility to SARS-CoV-2 infection. Ocul Surf 2020 Oct;18(4):537-544.
5. 5. Wu P, Duan F, Luo C, Liu Q, Qu X, Liang L, et al. Characteristics of ocular findings of patients with coronavirus disease 2019 (COVID-19) in Hubei Province, China. JAMA Ophthalmol 2020 May;138(5):575-578.
6. 6. Seah IY, Anderson DE, Kang AE, Wang L, Rao P, Young BE, et al. Assessing viral shedding and infectivity of tears in coronavirus disease 2019 (COVID-19) patients. Ophthalmology 2020 Jul;127(7):977-979.
7. 7. Hui KP, Cheung MC, Perera RA, Ng KC, Bui CH, Ho JC, et al. Tropism, replication competence, and innate immune responses of the coronavirus SARS-CoV-2 in human respiratory tract and conjunctiva: an analysis in ex-vivo and in-vitro cultures. Lancet Respir Med 2020 Jul;8(7):687-695.