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Seeing through the fog: mask-related data artefacts

Dr Alex Ioannidis


Face mask visual field data artefacts

One of Vision Eye Institute’s Victorian ophthalmologists, Dr Alex Ioannidis, is warning optometrists of the risk of artefactual data collection in a number of devices when patients wear face masks.

Last week, Dr Ioannidis saw firsthand the effect of face masks on visual field tests when two patients showed identical inferior, peripheral defects on their scans.

‘This type of artefact could potentially lead to unnecessary referrals for “glaucoma”,’ Dr Ioannidis says.

What is causing the artefactual data?

The mask creates a jet of warm, moist air that vents out from the top with each breath. When the warm air comes in contact with the cold device lens it condenses, causing the lens to fog and consequently distort the readings.

It may take several minutes for the fog to clear and could also potentially affect the results of the next patient’s test. A wipe down of the device lens may be required.

Fogging may also occur during other clinical examinations or imaging tests (e.g.  OCT, Pentacam and Optos), where the face comes in close proximity with the lens.

Clinical pearl

To get around this, Dr Ioannidis recommends taping the mask down across the bridge of the nose and the cheeks using paper tape (remember to wear gloves). This ensures the warm air is directed downwards, reducing the risk of lens fogging and artefactual imaging defects.

> Download Dr Ioannidis’s mask-related fogging resource.


Dr Alex Ioannidis is a cataract and anterior segment specialist. He practises at Vision Eye Institute Blackburn SouthVision Eye Institute Camberwell and Vision Eye Institute Coburg.

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