Reply to comment on: Staff perceptions of military chemical–biological–radiological–nuclear (CBRN) air-purifying masks during a simulated clinical task in the context of SARS-CoV-2

I would like to thank Drs Schumacher and Laidlaw for drawing attention to the limitation imposed by inadequate availability of corrective vision inserts for full-face air-purifying respirators, such as those used in our study. ¹ We agree this is a substantial concern that should ideally be addressed by providing healthcare workers with corrective vision inserts in advance of introducing these masks to clinical practice. We did not test the impact of this limitation in our study, as our study participants were self-selected and might therefore under-represent the views of the intensive care clinicians who require corrective spectacles. We did not record the proportion of our participants who usually required spectacles, and we recognise this as a limitation of our evaluation.

Custom-made optical inserts are routinely available to military personnel using masks such as those we tested, the Low Burden Mask (AirBoss Defense, Newmarket, Canada). However, in situations when the manufacture of such inserts is not possible, such as rapid deployment of masks during an unexpected emergency, it might be possible to provide a selection of standard-prescription inserts for staff with presbyopia, myopia or hyperopia. A population survey of 2595 people aged 40–60 years in Victoria, Australia, found 74.3% would be suitable for ‘off-the-shelf’ spectacles. ² Reasons for unsuitability in the remainder included corrected visual acuity <6/12 (3.4%), anisometropia >0.5 dioptres (10.6%), astigmatism ≥1.25 dioptres (6.6%) and both anisometropia and astigmatism (5.2%). Of those suitable for ‘off-the-shelf’ correction, providing spectacles in the range of +3.5 to −3.5 dioptres in half-dioptre steps provided suitable stock spectacles for 89.2%. Ready-made spectacles were acceptable to 90% of those randomised to receive them (instead of custom-made spectacles) in a trial involving 400 participants conducted in India. ³ Ready-made standard prescriptions are a commonly used inexpensive alternative to customised inserts for recreational diving masks. While not a preferred strategy, a selection of ready-made optical inserts for full-face air-purifying respirators could therefore be part of a disaster management plan that relies on these masks.