6.9  SARS-CoV-2 – ocular risk
The ACE2 receptors are also widely distributed in the superficial parts such as conjunctiva and cornea inferior parts such as iris, ciliary body, aqueous humor, trabecular meshwork, retina, and non-pigmented ciliary epithelium of the ocular globe which is mentioned out to be the intraocular renin-angiotensin system. Therefore, the distribution of ACE2 and TMPRSS2 protein must be taken into consideration to study the passage of infection through the ocular route [116]. Also, there is a chance for the virus to enter into the nasal cavity, which causes respiratory illness and the digestive system through the lacrimal canaliculi aided by the effectiveness of the tear film [117,118]. Out of 38 COVID-19 positive patients, 12 exhibited clinical manifestations, which include chemosis, epiphora, increased secretions, conjunctivitis, and conjunctival hyperemia. Researchers reported that patients exhibiting ocular symptoms would have elevated neutrophilic and lymphocytic counts, elated procalcitonin, lactate dehydrogenase, and C-reactive protein levels than those without ocular manifestations. The patients with ocular manifestations exhibited severe illness [119].
Even though there is no such evidence, the presence of ACE2 and TMPRSS2 protein in the corneal limbal stem cells suggests that the SARS-CoV-2 may enter the bloodstream and travel to the other parts including the brain [120]. Even though there is no viral load in the conjunctiva of the SARS-CoV-2 infected patients without conjunctivitis, the risk of transmission of the virus through tears is low [121]. The exact mechanism behind the ocular risk and SARS-CoV-2 need to be elucidated further.