Mouth-nose masks impair the visual field of healthy eyes

Background Mouth-nose masks have been requested to prevent the transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The aim of the present study was to investigate, if wearing a mouth-nose mask impairs the visual field function in normals. Methods Thirty eyes of 30 subjects were recruited for the present study. White-on-white perimetry (OCTOPUS 900; 90°) was done and sensitivity was analysed in 14 defined test points (P1-P14, inferior visual field) under 3 different test conditions while the subjects were wearing a mouth-nose mask: (I) 1.5 cm under the lower eyelid, nose clip not used (position 1.5cm_no_clip ); (II) 1.5 cm under the lower eyelid, nose clip correctly positioned (position 1.5cm_with_clip ); (III) 0.5 cm under the lower eyelid, nose clip correctly positioned (position 0.5cm_with_clip ). All data were compared to sensitivity without wearing a mouth-nose mask (reference). Mean Δ was calculated, being the difference between the results of each test condition and reference, respectively. Results Sensitivity was significantly different between position 1.5cm_no_clip and reference at 10 test points (p<0.05). Sensitivity at test point P7 was significantly different between position 1.5cm_with_clip and position 0.5cm_with_clip compared to reference (p<0.001), respectively. Mean Δ increased while wearing a mask at P7: position 1.5cm_with_clip (-8.3 dB ± 7.3 dB) < position 0.5cm_with_clip (-11.3 dB ± 9.5 dB) < position 1.5cm_no_clip (-20.1 dB ± 7.6 dB). Conclusion Visual field function was observed to be significantly impaired in the inferior-nasal sector while persons were wearing a mouth-nose mask, especially when the nose clip was not correctly used.