A number of controversies remain open in regards to eye care and infection control in relation to COVID-19. Whilst we are still looking to understand many aspects of the virus and how it functions, this article aims to provide an overview of our current understanding of the impact in an eye care context: 

• Ocular manifestations caused by COVID-19 are under reported (1) yet it is important to know when these        might occur and that they might be a source of infection for the general population as well as health and             eye care professionals.
   
• It is important to detect ocular manifestations as they can be early signs of onset for COVID-19 (13,14).
   
• Eye care is a fundamental primary care function and patients must feel confident that they can continue to         maintain their eye and vision care, and seek care when they identify any sudden change in their vision.
   
• Eye care professionals may be at a higher risk of contracting COVID-19 for three primary reasons:

Figure 1: Personal Protective Equipment worn to prevent exposure to SARS virus

What is COVID-19?

The COVID-19 outbreak was first reported by an ophthalmologist in China, Dr Li Wenliang, on 30 December 2019. Dr Wenliang worked at the Wuhan central hospital and is thought to have subsequently contracted the virus from an asymptomatic patient presenting for a glaucoma follow-up appointment. Sadly, he passed away from COVID-19 infection complications in February (1).

Coronaviruses are a family of enveloped positive-sense single-stranded RNA viruses that are known to cause the common cold, influenza and acute severe respiratory illness. The novel coronavirus disease 2019, named COVID-19 by the WHO, is caused by SARS-CoV-2 and is a highly transmittable and pathogenic viral infection that can lead to a severe acute respiratory syndrome. SARS-CoV-2 is a crown-shaped virus with a diameter of between 60 and 140 nm (which is extremely small when compared to other pathogens) capped by quite distinctive spikes, approximately 9 to 12 nm in length (see Figure 2).

Figure 2: SARS-CoV-2 Virus

Individuals can get infected with SARS-CoV-2 and be asymptomatic or have only mild symptoms while remaining highly contagious. The average incubation period is four to five days but can be up to 14 days. A risk of transmission by asymptomatic patients during the incubation period therefore significantly complicates the infection control measures required. 

How is COVID-19 spread?

COVID-19 is transmitted human-to-human through direct contact with secretions from an infected person or inhalation of droplets containing SARS-CoV-2. Like other airborne viruses, it can be transmitted when a person sneezes, talks or coughs, or via contaminated surfaces (e.g. door handles), hands, mouths, nose and eyes. The virus is known to survive in the environment depending on the temperature, humidity and nature of the surface, and can last for days on surfaces like plastic (2).

SARS-CoV-2 transmission through the eye has been the subject of debate. Indeed, exposed ocular surfaces can serve as a gateway for transmission because of the continuation of the mucous membranes via the puncta, and into the nasolacrimal duct, which can eventually deliver the virus to the lungs and gastrointestinal tract.(3) Unprotected ocular exposure was thought to be responsible for infections that occurred in the Wuhan Fever Clinic in January 2020  (4,5). 

A study examining the risk profile of ophthalmologists in Wuhan found that older age, a lack of PPE, insufficient sleep and less diligent hand hygiene were the risk factors for symptomatic COVID-19 contraction. (6) A recent systematic review of the literature relating to COVID-19 concluded that the virus is unlikely to bind to ocular surface cells to initiate infection (7), although the angiotensin- converting enzyme (ACE2) receptor required for infection has been identified in ocular surface cells  (8).

Which eye symptoms have been associated with COVID-19?

Ocular manifestations reported to be associated with COVID-19 have included acute conjunctivitis (pink eye), epiphora (excessive watering), discharge, photophobia (high light sensitivity), eye pain, and increased secretions (13).  A study in China showed that a third of patients with COVID-19 had ocular abnormalities and that these occurred more frequently in patients with severe COVID-19 (13).

Conjunctivitis is a rare manifestation of human coronavirus disease. The virus has been found to be present in approximately 25% of eyes and COVID-19 related conjunctivitis in approximately 10% of all hospitalised cases (1). Ocular complications such as viral conjunctivitis are most often found in the middle phase of illness (6,9). Moreover, "conjunctivitis can be the only presenting sign and symptom of COVID-19" (14). 

Figure 3: Conjunctivitis has been found to be associated with COVID-19

 In a patient with acute viral conjunctivitis examined on Day 13 of hospitalisation, the patient reported redness, foreign body sensation and tearing. Slit lamp examination identified bilateral moderate conjunctival injection, watery discharge and inferior palpebral conjunctival follicles.

Do human tears shed the COVID-19 virus?

The coronaviruses have been found to be able to adhere to ocular surface cells, with a wide difference in viral shedding patterns identified. A number of studies examining the viral load carried by humans had a range of results, from no presence to high loads at up to day 21 of the infection. 

One of the earliest studies from China detected viral RNA up to day 21 of the infection. The conjunctivitis significantly improved at day 15 and apparently resolved at day 20. (10) Further studies found that none of the patients had any evidence of viral particles in the tears, and the authors concluded that there was a low risk of transmission of SARS-CoV-2 from tears. (5) Studies are continuing to assess the tears and ocular surface as a source of infection and mode of transmission, and this topic remains unresolved. 

Protecting yourself and your patients, and limiting transmission of COVID-19 

While more research is needed, practitioners should exercise caution with touching a patient's eyes and inadvertently touching their own face. Health care workers who work in close proximity to hospitalised patients have been found to have higher rates of infection from COVID-19 and the need to protect eye care health professionals has been identified. (1) As practices begin to restart it is important to identify strategies to minimise exposure including;

• maintaining social distancing where possible; 
• installing physical screens and ask patients to wear a mask (if one is available); 
• implementing appropriate personal and practice infection control measures including cleaning,       sanitising and disinfecting all surfaces regularly and handwashing before and after all patient                 interactions; 
• wearing appropriate PPE, including white coat, mask, gloves and goggles;  
• carrying out remote exam/screening when possible; 
• using remote/online questionnaires to filter symptomatic patients.

Instruments that use high-speed air such as air-puff tonometers could theoretically cause aerosolisation and a risk of infection due to the generation of aerosols from the ocular surface. Non-disposable contact equipment used in tonometry, gonioscopy, pachymetry and biomicroscopy should be disinfected with ethanol-based solutions. The use of disposable attachments like tonometry probes is also recommended.

It should be noted that recent literature indicates that wearing contact lenses is still a safe form of vision correction as long as wearers continue to follow good hygiene practices.

Primary care and COVID-19

It is critical to ensure patients are appropriately informed about their need to maintain appropriate eye health routines and have regular appointments. In particular, patients must be reminded to:

• seek care should there be any sudden change in their vision;
• continue to attend important eye health appointments and follow-ups relating to the treatment of               conditions and diseases such as dry eyes, AMD and glaucoma. 

An increase in eye injuries has been found during the lockdown in Italy (11) and India. (12) This could be caused by an increase in do-it-yourself activities at home without suitable eye protection or children playing unsupervised while parents try to work from home. This is an important time to remind patients about the need for appropriate eye protection and other prevention measures to avoid eye injuries.

Watch for updates on COVID-19 and the eyes

New research on the potential for COVID-19 transmission from the human eye will continue.  Preliminary scientific reports show a potential pathway for the entry of and infection with SARS-CoV-2 in human ocular tissue as a route for spreading the virus. (8) Eye care professionals must remain vigilant with maintaining sanctioned office protocols to keep all stakeholders safe, and ensure patient and consumer confidence in their eye care experience.