Avoiding mask-related artefacts in visual field tests during the COVID-19 pandemic.

Aims To assess visual field (VF) pseudoprogression related to face mask use. Methods We reviewed a total of 307 VFs performed with a face mask (FPP2/KN95 or surgical masks) and compared them with prior VFs, performed before the pandemic. VFs with suspected pseudoprogression due to mask artefacts (VF test 1) were repeated with a surgical mask and an adhesive tape on its superior border (VF test 2) to distinguish from true VF loss. Several parameters including reliability indices, test duration, VF index (VFI), mean defect (MD) and pattern deviation probability plots were compared among last pre-COVID VFs, VF tests 1 and VF tests 2, using the Wilcoxon signed-rank test. Results We identified 18 VFs with suspected progression artefact due to masks (5.8%). In all of them, the median VFI and MD significantly improved after fitting the superior border of the mask, showing no significant differences with pre-COVID tests. The median fixation losses were significantly higher when wearing the unfitted mask (13% vs 6%,p=0.047). The inferior hemifield was the most affected, either as a new scotoma or as an enlargement of a prior defect. Conclusion Unfitted masks can simulate VF progression in around 6% of cases, mainly in the inferior hemifield, and increase significantly the rate of fixation losses. A similar rate of artefacts was observed using FPP2/KN95 or surgical masks. The use of a surgical mask with an adhesive tape covering the superior border may reduce mask-related artefacts, although concomitant progression cannot be ruled out in all cases.