Ocular tropism of coronavirus (CoVs): a comparison of the interaction between the animal-to-human transmitted coronaviruses (SARS-CoV-1, SARS-CoV-2, MERS-CoV, CoV-229E, NL63, OC43, HKU1) and the eye.Int Ophthalmol. 2021 Jan; 41(1):349-362.IO
Several studies have reported conflicting results on ocular manifestations and transmission of coronavirus disease 2019 (COVID-19) whose causative virus, SARS-CoV-2, belongs to the coronavirus family, the seventh recognized as a human pathogen and the third causing a severe clinical syndrome. COVID-19 primarily affects the lungs, similar to the other human coronaviruses. Comparing the relation between the animal-to-human transmitted coronaviruses (SARS-CoV-1, SARS-Cov-2, MERS-CoV, CoV-229E, NL63, OC43, HKU1) and the eye may contribute to determining their actual eye-tissue tropism and risk of ocular transmission.
Literature review was conducted via Pubmed.gov, Google Scholar and medRixv using the following keywords: COVID-19, SARS-CoV-2, SARS-CoV-1, MERS-CoV, CoV-229E, NL63, OC43, HKU1, conjunctivitis, tear swab, ocular expression, ocular symptoms and human angiotensin converting enzyme-2 expression. Studies with lack in methodology were excluded.
Sixteen observational studies were selected. The range for detection of viral RNA in tears was 0-8% for SARS-CoV-1 and 0-5.3% for SARS-CoV-2, while no reports were found for other coronaviruses. Ocular manifestations have been reported for NL63 and SARS-CoV-2. Ocular symptoms in the form of conjunctivitis/conjunctival congestion predominantly were detected in 65 (3.17%) out of 2048 reported patients with COVID-19 (range of 0.8-32%). Eye symptoms were not reported for the other coronaviruses.
Data aggregation for coronaviruses shows a relatively low eye-tissue tropism. Conjunctival congestion is an uncommon manifestation of COVID-19 similar to all human coronaviruses' infections. In a low percentage of patients, the virus can be excreted in ocular fluids at different stages of the infection, regardless of positive SARS-Cov-2 throat swab. Albeit high viral loads in ocular tissue seem to have relatively low prevalence, the eye should be regarded as a potential source of infection dissemination for COVID-19.