Visual Field Artifacts From Face Mask Use

Purpose: The coronavirus (COVID-19) pandemic has had a profound impact on how glaucoma care is delivered, necessitating reduced clinic flow, social distancing, and use of face coverings by patients and staff. This case highlights the need to be aware of improperly fitted face masks as a cause of artifact on standard automated perimetry (SAP). Clinical Presentation: A 32-year-old female underwent SAP with the 24-2 SITA Fast test of the Humphrey Field Analyzer wearing an ear-loop surgical face mask. At the end of testing, it was noted that the mask had ridden up the patient’s face. Small amounts of condensate were noted on the perimeter lens. Clinical Findings: SAP demonstrated good reliability indices but in both eyes, there was a marked reduction in sensitivity inferiorly. The glaucoma hemifield test was outside normal limits. It was ensured the upper border of the mask was well sealed with the loops secured around the ears and nasal strip of the mask pinched down. Visual fields were repeated and were found to be normal. Conclusions: Poorly fitting face masks represent a new cause of visual field artifact which may mimic pathologic field defects. Without careful attention during testing, the cause of such artifacts may not be apparent, especially as reliability indices may be normal. Adjustments to the fit of face masks may help prevent fogging or mask slippage and increase test reliability.

T he coronavirus (COVID-19) pandemic has had a profound and potentially permanent impact on how glaucoma care is delivered, necessitating reduced patient flow, social distancing, and use of face coverings by patients and staff. [1][2][3][4] Changes to clinical practice can have unintended consequences and we wish to highlight a case of visual field artifact on standard automated perimetry (SAP) due to an improperly fitted face mask. In normal circumstances, close monitoring of patients during the visual field testing is important to improve test reliability but this may be challenging with the need to social distance, and the use of face masks introduces a new potential barrier to reliable visual field testing.

CLINICAL PRESENTATION
A 32-year-old female underwent SAP with the 24-2 Swedish Interactive Threshold Algorithm (SITA) Fast test of the Humphrey Field Analyzer 3 (Carl Zeiss Meditec, Dublin, CA). The patient wore an ear-loop surgical face mask during testing. At the end of the test, it was noted that the surgical mask had ridden up the patient's face, and small amounts of condensate were noted on the perimeter lens. The visual fields showed good reliability indices but in both eyes there was a marked reduction in sensitivity inferiorly, worse in the left eye (Fig. 1). The glaucoma hemifield test was outside normal limits in both the eyes.
The patient was asked to reposition her face mask and to pinch down the nasal strip. It was ensured that the upper border of the mask was well sealed with the loops secured around the ears. Visual fields were then repeated and found to be normal (Fig. 2). While field defects secondary to the inappropriately positioned face mask resolved, the high false-positive rate in the right eye may also contribute to the absence of field defects on repeat perimetry.

DISCUSSION
To minimize the risk of infection from respiratory droplets, it is increasingly required that patients and staff wear masks covering their nose and mouth. 2 This case demonstrates a new cause of visual field artifact due to a poorly fitting face mask; a problem likely to become more prevalent with the increasing use of face coverings due to COVID-19. Without careful attention during testing, the cause of such artifacts may not be apparent, especially, as observed in the reported case, reliability indices such as fixation losses, false negatives, and false positives may be normal. Artifacts due to face masks may occur due to the edge of the mask riding up the patient's face, leading to a defect in the inferior visual field. However, other types of defect may occur, for example, due to the fogging of the perimeter's trial lens. As this case illustrates, the maskrelated artifact can mimic pathologic visual field defects, which may lead to an unnecessary referral or additional testing, something to be avoided at all times, but particularly during a pandemic.
Homemade and nonmedical grade face coverings are becoming increasingly common and this is likely to lead to patients using a variety of face masks during perimetry, some of which may be more prone to causing artifact. It has been highlighted that fluid-resistant surgical face masks with an ear-loop design can be more difficult to secure tightly enough to ensure a good seal compared with tie-back masks. 5 This may be particularly problematic for women as personal protective equipment may be designed to fit the face of the "average male." 6 Potential measures to improve the seal when using an ear-loop design mask include tying a knot in each of the elastic straps to shorten their length, or making a loop in each of the elastic straps to shorten their length, or to secure the straps at the back of the head rather than behind the ears. 5 The bridge of the nose may also be taped to prevent exhaled breath fogging the perimeter lens, a problem that ophthalmic surgeons will be familiar with from personal experience during their time as residents learning to use an operating microscope. 4 For tie-back surgical masks, knotting the 2 ties so they lie above and below the ear has been described to prevent superior venting and air leak, instead creating a "lateral vent." 7 The techniques suggested may be useful in preventing an upward direction of air leak, reducing condensation and fogging of the lens but it remains unclear whether they will prevent the mask riding up the face during perimetry.
Ordinarily, visual field technicians should remain in close proximity to patients undergoing perimetry to ensure the patient is correctly positioned and responding appropriately to the test. This may be more problematic if technicians are required to socially distance from patients, however, this case highlights that there may be a greater need to monitor patients during testing if they are wearing a mask. Some patients wearing masks during perimetry may also feel restricted and uncomfortable, potentially reducing test reliability. It is essential that ophthalmologists follow local recommendations on the use of face masks, and it is difficult to envisage a situation where an ophthalmologist would be justified in deviating from face mask guidance for the purpose of attempting to obtain a more accurate visual field test. This case though is useful to highlight face masks as a potential cause of visual field artifact.