Role of the Eye in Transmitting Human Coronavirus: What We Know and What We Do Not Know

Abstract

The outbreak of recently identified 2019 novel coronavirus (2019-nCOV) infection has become a world-wide health threat. Currently, more information is needed for further understanding the transmission, clinical characteristics, and infection control procedures of 2019-nCOV. Recently, the role of the eye in transmitting 2019-nCOV has been intensively discussed. Previous investigations about other high infectious human COVs, that is, severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV), may provide helpful information. In this review, we describe the genomics and morphology of human CoVs, the epidemiology, systemic and ophthalmic manifestations, mechanisms of human CoVs infection, and infection control procedures. The role of the eye in the transmission of SARS-CoV and 2019-nCOV is discussed. Although the conjunctiva is directly exposed to extraocular pathogens, and the mucosa of ocular surface and upper respiratory tract is connected by nasolacrimal duct and share same entry receptors for some respiratory viruses. The eye is rarely involved in human CoVs infection, conjunctivitis is quite rare in patients with SARS-CoV and 2019-nCoV infection, and COV RNA positive rate by RT-PCR test in tears and conjunctival secretions from patients with SARS-CoV and 2019-nCoV infection is also very low, which imply that the eye is neither a preferred organ of human COVs infection, nor is a preferred gateway of entry for human COVs to infect respiratory tract. However, pathogens exposed to the ocular surface might be transported to nasal and nasopharyngeal mucosa by constant tear rinsing through lacrimal duct, and then cause respiratory tract infection. Considering close doctor-patient contact is quite common in ophthalmic practice which are apt to transmit human COVs by droplets and fomites, hand hygiene and personal protection are still highly recommended for health care workers to avoid hospital-related viral transmission during ophthalmic practice.

Experimental Efficacy of the Face Shield and the Mask against Emitted and Potentially Received Particles

“…The ocular mucosa and the nasopharynx are connected by the nasolacrimal duct. When splashes reach the cornea or conjunctiva, they can penetrate the nasolacrimal duct and be transported to the nasopharynx and trachea [ 44 , 45 ]. Ocular manifestations seem frequent, and high-frequency hand–eye contact correlates with conjunctival congestion [ 46 , 47 ].…”

Shedding of SARS-CoV-2 in feces and urine and its potential role in person-to-person transmission and the environment-based spread of COVID-19

“…Assuming a worst case human feco-oral infectious dose of 10 3 gc/person, this would necessitate that levels of infectious SARS-CoV-2 greater than 3.3 × 10 4 gc/l would be needed to cause concern. It should also be noted that while the eyes are often in contact with water during recreational activities, this route of SARS-CoV-2 entry into the body is thought to be minimal, particularly in comparison to ingestion of water and oral/nasopharynx mucosal exposure ( Sun et al, 2020b ; Deng et al, 2020 ). This analysis for SARS-CoV-2 contrasts with other viruses transmitted by the fecal-oral route (e.g.…”

Ocular Symptoms of SARS-CoV-2: Indication of Possible Ocular Transmission or Viral Shedding

“…6,40 Though the virus-containing fluid can be absorbed by the conjunctiva, sclera, or cornea, the majority of fluid exchange is between the nasopharyngeal space, through absorption by the epithelial lining of the lacrimal duct. 15,49 The anatomical linkage of the ocular mucosal immune system (composed of the lacrimal glands and ocular surface; including the tear film, conjunctiva, and corneal epithelium) with nasopharyngeal space supports the immunological interdependence between ocular and respiratory tract tissues. 40,49 However, despite the ocular mucosal surface being protected from infectious organisms by an array of antimicrobial factors (lactoferrin, lysozyme, immunoglobulin A (IgA), and cationic peptides) present in the tear film and blink shear forces which together limit access to the corneal epithelium, 47 CoV genomic fractions have been detected in the tear fluid of symptomatic and asymptomatic patients.…”

“…15,49 The anatomical linkage of the ocular mucosal immune system (composed of the lacrimal glands and ocular surface; including the tear film, conjunctiva, and corneal epithelium) with nasopharyngeal space supports the immunological interdependence between ocular and respiratory tract tissues. 40,49 However, despite the ocular mucosal surface being protected from infectious organisms by an array of antimicrobial factors (lactoferrin, lysozyme, immunoglobulin A (IgA), and cationic peptides) present in the tear film and blink shear forces which together limit access to the corneal epithelium, 47 CoV genomic fractions have been detected in the tear fluid of symptomatic and asymptomatic patients. 21 Perhaps, entrapment of microorganisms in secreted mucins and ocular surface defects increase the likelihood of colonization by infectious agents, underscoring the potential for ocular involvement following an outbreak of SAR-CoV-2 infection.…”

“…The effectiveness of transmission of the virus into host tissues is modulated by the invasiveness of the virus, viral-host receptor membrane interaction, and immune mediators of the host. 28,49 MERS-CoV and most α-CoVs have been identified to utilize dipeptidyl peptidase 4 and aminopeptidase N as an entry receptor of their host cells, respectively. 49,50 The cellular entry receptor utilized by HCoV-NL63, SARS-CoV and 2019-nCoV is Angiotensin-Converting Enzyme 2 (ACE-2) 51 (Figure 2).…”