Until we have a vaccine and see a reduction of COVID-19 cases down to zero, we must adjust and take every precaution possibly to protect our staff, as well as our patients.
Much has been published about the risks of contracting Covid-19 from tears and the precautions that need to be taken. This article will evaluate the risks surrounding the most commonly performed procedures during an ophthalmic exam, focusing particularly on procedures requiring contact with the eye, such as tonometry.
Given that the COVID-19 pandemic involves a new virus, which has spread and behaved unpredictably, our understanding of patient management in this new reality has evolved. Consider that in March, a study published in the journal Ophthalmology concluded that it was unlikely that COVID-19 patients shed virus through their tears.1
However, less than two months later, a new study from Johns Hopkins University, Baltimore, United States, concluded differently: “These results indicate that ocular surface cells including conjunctiva are susceptible to infection by SARS-CoV-2, and could therefore serve as a portal of entry as well as a reservoir for person-to-person transmission of this virus.”2 They added that the results showed that the ocular surface could be an even more significant reservoir for virus particles than suggested by other recent clinical studies.2
Given these recent findings, we must be vigilant about reducing the risk of virus transmission for our staff, as well as our patients. In our clinic, we have implemented specific safety measures that should reduce the risk of infections in general.
These include: providing face masks to each patient when entering the clinic; measuring body temperature by a non-contact method; excluding patients with any potential COVID-19 symptoms; frequent ventilation of all rooms; adding barriers around instruments and the reception area; and disinfection of all surfaces every hour. We have also made it mandatory for the entire clinic team to wear gloves, safety glasses and facemasks.
According to a World Health Organisation-funded study, face masks and eye protection/safety glasses provide the best protection in reducing the risk of infection. Writing in the Lancet, the researchers looked at 216 studies with more than 25,000 COVID-19 patients and found that face masks resulted in the largest reduction of risk (95% CI: 0.07–0.34), followed by eye protection (95% CI: 0.12–0.39).3
In addition, most eyecare practitioners very quickly adopted the placement of a plastic barrier around their slit lamps in order to reduce transmission risk. But what about other routine eye exams – what are the risks and how can we minimise them?
Highest risk of exposure
Among the first recommendations made by the American Academy of Ophthalmology and other ophthalmic societies was to place a plastic shield around the exterior of slit lamps.4 But how effective is this barrier?
A recent study published in a letter to the editor in the British journal Eye tested two sizes of plastic shields using a breathing simulator to replicate a normal adult breathing pattern.5
Researchers measured spray without the plastic barrier, with an 11x11x0.2-cm barrier and a larger 45x44x0.2-cm barrier.
They then measured the number of particles over a 1-minute period. The slit lamp arm was offset at 60° and the test was repeated five times for each shield. A linear regression analysis determined the effectiveness of no barrier and the two barriers, as well as the particle count.
Without any shield in place, the mean log particle count was 3.59 (95% CI: 3.48–3.70). With the standard shield in place, there was a reduction to 3.01 (95% CI: 2.90–3.13; P<0.01) and a further drop was seen with the larger barrier in place, which lead to a mean count of 2.62 particles (95% CI: 2.50–2.73; P<0.01).5
However, while the larger barrier provided the greatest reduction in particle transmission, the authors pointed out that the larger shield can lead to contact transmission of the virus due to the need to manipulate the slit lamp arm or during tonometry. As a result, the authors noted that the barrier should be used in combination with hand hygiene and surface cleaning.5
Imaging devices, including OCT
A highly useful article published in the June issue of the journal Glaucoma outlines the risks and best practices for various ophthalmic tests, including the use of imaging devices, such as those used for optical coherence tomography. The obvious contact points on these devices are the chin rest and head guard where the patient has direct contact, but if the patient is unmasked, droplets from breathing and speaking can also contaminate the surface of the device.6
While cleaning and disinfection after each patient is the obvious solution, most imaging device manufacturers have specific recommendations about how this is done without damaging these devices. All manufacturers have developed guidelines for this purpose.
This test places both the patient and the technician at risk due to its lengthy nature and the need for the technician to be in proximity to the patient while the patient is performing the visual field test. The corrective lens and bowl of the perimeter can be exposed to respiratory droplets, while the response button, occluder, head strap and chin rest are in direct contact with the patient. The authors suggest replacing the occluder with a disposable amblyopia patch or gauze, as well as following manufacturers’ cleaning and disinfecting instructions.6
This procedure has attracted a certain amount of debate given that the two forms of tonometry—contact and non-contact— have the potential to result in infection transmission.With contact tonometry, the risk is clear from the name – the tonometer encounters the cornea.
Published studies have shown that applanation tonometry can potentially transmit a number of infectious diseases, including adenovirus B and herpes simplex virus 1, while reusable tonometer prisms are able to transmit hepatitis B & C, as well as HIV and Creutzfeldt-Jakob disease.6 The AAO notes that there is no optimal way to disinfect Goldmann tonometers without potentially damaging the device and recommends the use of disposable tonometer prisms, if available, to reduce the risk of viral transmission.4
In a separate letter to the editors of Eye published online in April, ophthalmologists from the University of Hong Kong noted that they had suspended all tests that might result in micro-aerosol, including non-contact tonometry (NCT).7 Shabato et al. note in their article that there is no set evidence that there is aerosol transmission with current devices and also point out that NCT enables clinic staff to put more distance between themselves and patients.
However, surfaces around the testing area should be disinfected between patients. The Centres for Disease Control and Prevention also recommends caution in performing tests that result in “aerosolisation of viral particles.”
Interestingly, a 1991 study of NCTs attempted to show the alleged danger of the air puff approach using fluorescence photography to capture droplet splatter when drops were instilled into eyes as the puff of air was applied. However, they could not replicate it with just the patients’ tears.8
Can safety rules make vision exams 100% safe?
Based on our review of literature and recommendations that have been published in recent months, it is clear that both societies and ophthalmic equipment manufacturers are providing as much guidance as possible to help clinicians navigate these unchartered waters. It is also certain that, based on our current knowledge of the role of the tear film in COVID-19 patients, with proper safety, cleaning and disinfecting procedures, the risk of viral transmission will remain low.
Of course, virus transmission can never be completely excluded by the discussed transmission pathways. The remaining risk under these circumstances must be estimated.
Wearing masks and safety glasses is a good barrier against direct droplet transmission even within the proximity between patient and examiner in the case of Goldman applanation tonometry or rebound tonometry. Gloves protect the examiner while he touches the patient’s face and eyes. But care must be taken to avoid cross-contamination of surfaces or other instruments, even when wearing gloves.
In addition to clinic staff wearing masks, it is critical that patients are also masked in order to prevent aerosol contamination from breathing or speaking,9 given that aerosols induced by breathing or sneezing have a much higher virus concentration and are much more likely to be infectious. Recent experiments in clinics have shown that glasses worn by the patient steam up by their breath even when a mask is being worn. This illustrates that aerosol production is difficult to avoid in clinical practice.
These examples demonstrate that potential risks caused by the proximity between patient and examiner in case of applanation and rebound tonometry can be reduced in theory, however, in clinical practice potential risks remain. Again, distancing between patients and examiners and frequent ventilation should be the main ways of minimising these risks, as well as the use of NCT.
The Johns Hopkins study sends a strong message to the ophthalmic community – that ACE2 (the receptor for SARS-CoV-2) and TMPRSS2 (a cell surface-associated protease that facilitates viral entry) are present in conjunctival and corneal epithelial cells. This means that the ocular surface can be a potential site of infection or serve an entry port for the virus to enter the blood stream. In addition, they conclude that ocular virus shedding does have the potential to infect others.2
Clearly, in order to provide eye care for our patients, resuming practice is the right thing to do. However, until we have a vaccine and see a reduction of COVID-19 cases down to zero, we must adjust and take every precaution possibly to protect our staff, as well as our patients. The use of tests such as NCT, as well as placement of plastic barriers, provide distance between the clinic team and patients, reducing the risk of aerosol viral transmission.
We have implemented specific safety items in our clinic that should reduce the risk of infections in general. By adhering to these specific safety measures as well as implementing some other rules, we consider NCT measurements to be safe with a very low remaining risk.
The greatest threat to professional healthcare providers arises from the close doctor-patient proximity, which is reduced in the case of NCT measurements. Complete avoidance of tonometry in the clinic could cause much more harm than the very low remaining risk for an infection if all safety rules are considered.
About the Author
Dr Omid Kermani, MD
Dr Kermani is medical director, Augenklinik Neumarkt, Cologne, Germany. He has no financial disclosures.