The now-ubiquitous face mask generally doesn’t interfere with an ocular exam, but new research cautions that poorly fitting masks worn by glaucoma patients can cause visual field (VF) artifacts, which may be interpreted as disease progression, or make the tests less reliable.

The investigation included 127 glaucoma patients who underwent standard automated perimetry. In patients with low test reliability or VF changes, testing was repeated after repositioning and taping masks. A total of 101 patients wore surgical masks, and 26 others wore cloth masks.

The researchers found low levels of testing reliability in 23 patients (18%) and inferior VF defects in three patients (2%). The most common testing issues were increased fixation losses and false positives.

Additionally, low testing reliability was notably higher in patients who wore cloth masks compared with those in surgical masks (48% vs. 10%).

Eyeglass fogging due to face masks prior to testing was a strong predictor of trial lens fogging and low testing reliability. In all repeated tests, the patients’ reliability parameters improved and inferior VF artifacts disappeared.

“Careful assessment of structure-function correlation and repeated VF tests with the taped mask are critical to differentiate between artifacts and abnormalities,” the researchers wrote in their paper.