Ocular renin-angiotensin system with special reference in the anterior part of the eye

Management of COVID-19 in Ophthalmology

From its outbreak in early 2020, the new SARS-CoV-2 infection has deeply affected the entire eye care system for several reasons. Since the beginning of the COVID-19 pandemic, ophthalmologists were among the "high-risk category" for contracting the SARS-CoV-2 infection based on the notion that the eye was suspected to be a site of inoculation, infection, and transmission. Clinical ophthalmologists have been required to learn and promptly recognize the ocular manifestations associated with the COVID-19 disease, with its treatments and vaccinations. Restriction measures, lockdown periods, guidelines to prevent SARS-CoV-2 infection transmission, and the use of telemedicine and artificial intelligence modalities have induced profound modifications. These changes, which are most likely to be irreversible, influence routine clinical practice, education, and research, thus giving rise to a "new ophthalmology in the COVID era". This book chapter aims to provide several notions regarding COVID-19 in ophthalmology, including the SARS-CoV-2 virus infection and transmission modalities; the ocular manifestation associated with the COVID-19 disease; the drugs and vaccines used for COVID-19; the precautions adopted in the ophthalmic practice to limit the spread of the virus; the consequences of the pandemic on the ophthalmic patients, clinicians, and the entire eye care system; and, the future of ophthalmology in the era of "COVID new normal".

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

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Many Faces of Renin-angiotensin System - Focus on Eye

The renin-angiotensin system (RAS), that is known for its role in the regulation of blood pressure as well as in fluid and electrolyte homeostasis, comprises dozens of angiotensin peptides and peptidases and at least six receptors. Six central components constitute the two main axes of the RAS cascade. Angiotensin (1-7), an angiotensin converting enzyme 2 and Mas receptor axis (ACE2-Ang(1-7)-MasR) counterbalances the harmful effects of the angiotensin II, angiotensin converting enzyme 1 and angiotensin II type 1 receptor axis (ACE1-AngII-AT1R) Whereas systemic RAS is an important factor in blood pressure regulation, tissue-specific regulatory system, responsible for long term regional changes, that has been found in various organs. In other words, RAS is not only endocrine but also complicated autocrine system. The human eye has its own intraocular RAS that is present e.g. in the structures involved in aqueous humor dynamics. Local RAS may thus be a target in the development of new anti-glaucomatous drugs. In this review, we first describe the systemic RAS cascade and then the local ocular RAS especially in the anterior part of the eye.