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Summary


How Does Covid-19 Affect the Eyes: Covid-19 can sometimes cause ocular symptoms, although the documented prevalence varies widely — from 0% to 31.6%. The most common ocular signs are red-eye, conjunctivitis, light intolerance, and eye itchiness.
Covid-19 Can Infect the Eyes: SARS-CoV-2 genes have been discovered in the conjunctiva, retina, and eye secretions of infected patients. The ACE2 receptor is also present in the eye conjunctiva and retina. And SARS-CoV-2 replication in conjunctival cells has been confirmed. However, Covid-19 may still harm the eyes in other ways, such as by inducing excessive inflammation, hypoxia, or blood clotting.
Covid-19 Eye Transmission Remains Unclear: Although there is only anecdotal and no hard evidence of eye transmission, health authorities still advice for eye protection in healthcare workers. Even if eye transmission is possible, it should be of lesser real-life significance than droplets.

How Covid-19 Affect the Eyes


A paper on this topic, “Ocular manifestations of coronavirus disease 2019,” is published in Clinical and Experimental Ophthalmology in June. Researchers in Turkey examined 93 hospitalized patients with Covid-19, of which 20 (21.5%) presented at least one ocular (eye) symptoms. The specifics are:
• Hyperemia (red eye): 20 (21.5%) patients.
• Epiphora (excessive tear flow): 9 (9.7%) patients.
• Increased secretion (of green or yellow eye fluid): 6 (6.5%) patients.
• Chemosis (swelling of conjunctiva): 3 (3.2%) patients.
• Follicular conjunctivitis (more severe chemosis): 8 (8.6%) patients.
• Episcleritis (inflammation of eye sclera): 2 (2.2%) patients.
• Photophobia (intolerance to light): 15 (16.1%) patients.
• Itchiness: 13 (15.7%) patients.
• Burning sensation: 7 (8.4%) patients.
• Gritty feeling (eye irritation that feels like sand): 5 (6.0%) patients.
• Blurred vision: 4 (4.8%) patients.
Risk factors for Covid-19 ocular problems were old age and elevated inflammation — as indicated by increased fever, neutrophil/lymphocyte ratio, C-reactive protein, and erythrocyte sedimentation rate. However, they did not examine other disease outcomes, such as hospital stay or death rate.
Other research has also documented cases of ocular signs in Covid-19, as summarized in a table of an earlier June review titled “COVID-19 and the eye: how much do we really know? A best-evidence review.” The review shows that the prevalence of Covid-19 ocular symptoms varies widely from 0% to 31.6%. (Note that this review did not include the study above.)

Source (CC BY): Emparan et al. (2020). COVID-19 and the eye: how much do we really know? A best evidence review. Arquivos Brasileiros de Oftalmologia, 83(3), 250–261. https://doi.org/10.5935/0004-2749.20200067

On the Retina and Optic Nerve Connection


A May research paper, “Detection of SARS-CoV-2 in Human Retinal Biopsies of Deceased COVID-19 Patients,” found SARS-CoV-2 genetic material in the retina of three out of 12 deceased patients. And prior research has, in fact, found ACE2 expression in the human retina.
(The retina is the back part of the eye where the optic nerve is placed. Any information the retina receives is relayed to the brain via the optic nerve.)

Cancer Research UK / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)


A May study in The Lancet, “Retinal findings in patients with COVID-19,” has also shed light on this topic. Using a non-invasive eye imaging technique called optical coherence tomography (OCT), they saw damages to the retina and optic nerve in all 12 Covid-19 patients tested. However, the good news is that these patients showed no visual impairment. “Although animal models [of coronaviruses] suggest ocular lesions could include retinitis and optic neuritis, this is, to the best of our knowledge, the first report of retinal findings possibly associated with Covid-19 infection in humans,” the authors closed.
Later in July, another published OCT study, “Optic nerve analysis in COVID‐19 patients,” found increased inflammation of the optic nerves in all five patients tested, compared to when they did not have Covid-19. And, again, none had a visual loss, which implies that the optic nerve inflammation may not be severe enough to rupture the nerve completely.

Covid-19 Can Infect the Eyes


Back in February, Chinese researchers (Xia et al.) detected, for the first time, SARS-CoV-2 genetic material in tears and conjunctival secretions in one patient (3.3%) out of 30. That one patient also had conjunctivitis (inflamed eye membranes), while the remaining 29 did not have it.
Other research shows a similar trend. Sometimes SARS-CoV-2 is present in eye fluids, and sometimes it is not; the prevalence ranges from 0% to 7.14%, as compiled in a table of the June review. These data suggest that it is rare for SARS-CoV-2 to infect the eyes, although it can happen sometimes.

Source (CC BY): Emparan et al. (2020). COVID-19 and the eye: how much do we really know? A best evidence review. Arquivos Brasileiros de Oftalmologia, 83(3), 250–261. https://doi.org/10.5935/0004-2749.20200067


The fact that the eye conjunctiva expresses ACE2 receptors, according to a study in Nature, supports the possibility of Covid-19 eye infection. A July paper in the Lancet Respiratory Medicine confirms that SARS-CoV-2 replicates in conjunctival cells (in a lab dish) to a greater extent than SARS-CoV-1. “The conjunctival epithelium and conducting airways appear to be potential portals of infection for SARS-CoV-2,” the study authors concluded.
Even if SARS-CoV-2 does not infect the eyes, it may still harm the eyes in indirect ways. Covid-19-induced excessive inflammation, hypoxia (low oxygen levels in the blood), or blood clotting all can disturb distant organs.

Covid-19 Eye Transmission Remains Unclear


There are also a few anecdotal reports of Covid-19 transmission via the eyes. In brief, healthcare workers who wore a mask and appropriate personal protective equipment (PPE), but no eye protection, somehow contracted Covid-19 and conjunctivitis.


But the verdict is still out there. “Although there is currently no confirmed conjunctival transmission route, the authors agree with the WHO and other organizations´ recommendations that PPE must include eye protection such as goggles or face shields,” stated the June review. However, even if Covid-19 eye transmission is possible, it should be of lesser real-life significance than droplets.