Defining the risk of COVID-19 in Certain Standard-of-Care Diagnostic Tests - EuroTimes

Defining the risk of COVID-19 in Certain Standard-of-Care Diagnostic Tests

Omid Kermani MD

Virus transmission can never be completely stopped but precautions can be taken to reduce the risk of transmission of the novel coronavirus, while maintaining high standards of patient care, writes Omid Kermani MD, Augenklinik am Neumarkt, Cologne, Germany

In our clinic, we have implemented specific safety items that should reduce the risk of infections in general. These rules include providing face masks to each patient when entering the clinic, measuring body temperature by non-contact methods, excluding patients with any potential COVID-19 symptoms, frequent ventilation of all rooms, adding barriers around instruments and reception and disinfection of all surfaces, every hour. Wearing gloves, safety glasses and face masks for the whole clinical team while being in contact with the patient is also mandatory. 

According to a WHO-funded study, face masks and eye protection/safety glasses provide the best protection in reducing the risk of infection. The Lancet study looked at 216 studies with more than 25,000 COVID-19 patients found that face masks resulted in the largest reduction of risk with a 95% confidence interval of 0.07 to 0.34, followed by eye protection with a 95% confidence interval of 0.12 to 0.39.

In addition, most eyecare practitioners very quickly adopted the placement of a plastic barrier around the slit lamp in order to reduce aerosol transmission of the virus, which a recently published Johns Hopkins University study indicates is a definitive concern when seeing patients.

The results of the John Hopkins study found that the ocular surface could be an even more significant reservoir for virus than suggested by other recent clinical studies: [and] “could therefore serve as a portal of entry as well as a reservoir for person-to-person transmission of this virus”. 

In addition to the slit lamp exam, what other ophthalmic tests pose the greatest potential for viral transmission due to close contact with the patient?

Two that have been highlighted in a recent review article in the Journal of Glaucoma are visual field testing and tonometry – both contact and non-contact.

With visual field testing, both the patient and the technician at risk due to the length of the test, and the need for the technician to be in proximity while the patient is performing the visual field test. The corrective lens and bowl of the perimeter can be exposed to respiratory droplets and the authors note: “The duration of viral particle presence on the bowl surface, how long the particles remain suspended within the bowl, and whether the viral particles can be dislodged or resuspended by normal breathing or talking by the patient undergoing testing is unknown.”3  The response button, occluder, head strap and chin rest are also 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.

With either form of tonometry, there is the potential for infection transmission.

With contact tonometry, the risk is in the name – the tonometer comes into contact with the cornea. Earlier published studies have shown that applanation tonometry could potentially transmit a number of infectious diseases, include adenovirus B and herpes simplex virus 1, while reusable tonometer prisms could transmit hepatitis B & C, as well as HIV and Creutzfeldt-Jakob disease.

In addition, as the American Academy of Ophthalmology notes, 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. However, disposable tonometers can be expensive.

On the other hand, non-contact tonometry, which utilises a puff of air to assess the pressure of the eye, is viewed suspiciously as it is assumed that the air puff will cause dispersal of the tear film.  University of Hong Kong ophthalmologists indicated that they had suspended all tests that might result in micro-aerosol, including non-contact tonometry in a letter to the journal, Eye.  However, the Glaucoma article authors contend that there is no set evidence that there is aerosol transmission with current devices and note that non-contact tonometry enables clinic staff to put more distance between themselves and patients. 

Interestingly, a 30-year-old study on the alleged dangers of non-contact tonometers actually showed that the air puff did not produce any aerosol transmission from tears. In this study, researchers performed the air puff on eyes with a normal tear layer and then using a fluorescein-stained drop. When the air puff was administered after the drop, there was spraying of the fluid. However, when the air puff was administered to the natural tear layer, no droplets were found on nearby surfaces and there was no aerosol transmission.

Can safety rules make vision exams 100% safe?

Based on our review of literature and guidance, we think it’s clear that virus transmission can never be completely stopped. Wearing masks and safety glasses are good barriers against direct droplet transmission even within the proximity between patient and examiner. Gloves protect the examiner while touching the patient’s face and eye. But care must be taken to avoid cross-contamination of surfaces or other instruments, even when wearing gloves. 

While there is a risk of viral transmission from the eye, aerosols with higher virus concentrations come from breathing or speaking. In our experience, these aerosols cannot be avoided completely even when both patient and doctor are wearing masks. This is indicated by the fact that glasses become steamed-up while the patient is wearing a mask. For this reason, distance between doctor and patient should reduce the risk. Most importantly, frequent ventilation is the best protection against potential infection by aerosols as the Robert-Koch Institution points out. The highest risk of infection with SARS-CoV-2 virus is given by direct droplet transmission or by fomites. The highest risk for these events is given by close doctor-patient contact over a longer period of time.

References on request



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