Risk of airborne COVID-19 transmission low during visual field testing
The risk of airborne transmission of COVID-19 between patients during Humphrey visual field testing is low, according to data published in the Journal of Glaucoma.
“There is no significant difference between aerosol count in the bowl of a HFA before, during and after testing,” Nikhil Jain, MBBS, of University College Hospitals NHS Foundation Trust in London, and colleagues wrote. “This suggests the risk of airborne transmission of COVID-19 is low between subsequent patients.”
Researchers compared data from two experiments to determine the likelihood of COVID-19 transmission among patients undergoing Humphrey visual field testing by assessing the presence of air particles in the bowl of a Humphrey visual field analyzer (HFA).
The first experiment was conducted with only an investigator in the room. After allowing 5 minutes for dynamic air flow to stabilize, the investigator placed a particle counter in the bowl of the HFA while the analyzer was turned off. The counter then pumped 0.9 L of air through itself over 21 seconds, per recommended settings. This process was repeated 20 times with the analyzer turned off and on.
In the second experiment, researchers introduced a mock patient who underwent a 24-2 SITA standard visual field test at the HFA, and the particle counter was again placed in the bowl of the analyzer. Twenty readings were taken with both the patient present and after the patient had stepped away.
Particulates of all sizes were found to be notably reduced in the HFA bowl when the machine was turned on, indicating that the current produced by the analyzer adequately pushes air out of the bowl, rather than allowing it to stagnate. In addition, the particle count was unaffected by the presence of a patient, “suggesting that aerosols breathed out by the patient are not able to remain in suspension in the bowl because of the ventilation current,” researchers wrote.
“This confirms the manufacturer’s claim that the ventilation current of the HFA perimeters push air from within the bowl past the patient,” Jain and colleagues wrote. “This likely reduces the risk of airborne transmission of respiratory pathogens between consecutive patients using the machine as aerosols are unable to remain in suspension in the bowl.”
Perspective
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The COVID-19 pandemic has changed every aspect of health care, including optometry. Throughout the past 2 years, doctors have had to balance the difficult decisions of providing optimal ophthalmic care while minimizing unnecessary risk of COVID-19 exposure. Our care for patients relies heavily on auxiliary diagnostics such as visual field testing. Formal visual field testing with a HFA obviously poses some risk through potential contact, droplet and aerosol transmission.
This study is reassuring, as it demonstrates the potential risk of airborne transmission can be reduced with the HFA. In addition to reducing contact and droplet transmission through wiping down surfaces and spraying the bowl with isopropyl alcohol, ventilation by the instrument pushes air out of the bowl and reduces the amount of aerosol particles in the bowl.
Furthermore, the number of particles was found to be no different during the test with a patient and after the test when the patient had left.
In clinical practice, these factors, in addition to mask wear and adequate room ventilation, will significantly reduce the potential risk of transmission during testing. Overall, I am reassured that performing visual field testing can be a low-risk procedure for our patients.
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