Risk of Airborne COVID-19 Transmission While Performing Humphrey Visual Field Testing

Abstract

Precis: Designing and demonstrating an experiment that shows the risk of airborne transmission of COVID-19 between patients having visual fields analyzed is low. Purpose: The aim was to investigate the possibility of airborne transmission of COVID-19 during Humphrey visual field testing in a real-world scenario. Methods: A particle counter was placed within the bowl of Humphrey visual field analyzer (HFA) before and after turning on the machine to ascertain the effect of the air current produced by the ventilation system on aerosols. A second experiment was run where the particle counter was placed in the bowl and recorded particulates, in the air, as a 24-2 SITA standard was performed by a mock patient and then again immediately after the patient had moved away. We measured aerosol particle counts sized ≤0.3 μm, >0.3≤0.5 μm, >0.5≤1 μm, >1≤2.5 μm, >2.5≤5 μm, and >5≤10 μm. Results: Particulates of all sizes were shown to be significantly reduced within the bowl after turning the machine on, demonstrating that the air current produced by the HFA pushes air out of the bowl and it cannot stagnate. There was no significant difference in measurement of aerosol while there was a patient performing the test and immediately after they had moved away, suggesting that aerosols breathed out by the patient are not able to remain in suspension in the bowl because of the ventilation current. Conclusion: There is no significant difference between aerosol count in the bowl of a HFA before, during and after testing. This suggests the risk of airborne transmission of COVID-19 is low between subsequent patients. This is in keeping with manufacturer’s guidance on Humphrey visual field testing.

Visual fields in glaucoma: Where are we now?

“…This confirms the manufacturer's claim that the ventilation current of the HFA perimeters pushes air from within the bowl past the patient. It is unlikely that whether or not a patient wears a mask during testing itself has any bearing on airborne transmission 6 …”

“…Fortunately, there are studies to suggest that airborne transmission of COVID-19 within the field analyser bowl was low. 6 Jain et al showed that particulate count in suspension within the bowl of a Humphrey visual field analyser (HFA) was significantly reduced by the activation of the cooling fans present within the machine and, crucially, that this particulate count is unaffected following use of the machine by a patient who is not wearing a mask. This confirms the manufacturer's claim that the ventilation current of the HFA perimeters pushes air from within the bowl past the patient.…”

“…It is unlikely that whether or not a patient wears a mask during testing itself has any bearing on airborne transmission. 6 It has been suggested that the number of visual fields performed should be minimised to reduce the potential for viral transmission. The recommended time interval between visual field tests should in principle, depend on the glaucoma's severity and the predicted rate of progression.…”

Eye damage in COVID-19. Part 1: Involvement of the eye in SARS-CoV-2 virus transmission and anterior segment complications

“…Наконец, немаловажен вопрос о риске заражения SARS-CoV-2 во время офтальмологических обследований и операций. Так, в литературе обсуждается риск заражения данной инфекцией при тонометрии [5,42] и периметрии [43].…”

Response to Letter to the Editor: The Impacts of Face Mask Use on Standard Automated Perimetry Results in Glaucoma Patients

“…2 We would also like to know the range of refractive errors among the study population, as myopic patients show a significant influence of refraction on the differential light sensitivity in the peripheral visual field, whereas hyperopic eyes show in the central visual fields. 3 Ma et al, 4 in their paper, demonstrated an efficacy of 97.14% and 95.15% for surgical and homemade (made of 4-layer kitchen paper and 1-layer cloth) masks respectively in blocking severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. Osterholm and colleagues reported the physical properties of cloth mask and the frequency, effectiveness of cleaning cloth masks.…”