Good news for glaucoma clinics: face masks don't meaningfully skew intraocular pressure (IOP) readings at the population level. A randomized controlled trial published in the Journal of Glaucoma tested 94 eyes from 47 glaucoma patients, measuring IOP with a Goldmann applanation tonometer under three conditions — no mask, surgical mask, and KN95 mask. Average IOP differed by less than 0.5 mm Hg across all three scenarios, a statistically insignificant gap.

But zoom in on individual patients, and the picture gets more nuanced. About one-third of participants showed IOP differences of at least 3 mm Hg between mask conditions — a gap that could influence clinical decisions in glaucoma management. Researchers attribute this variability to mask fit on different facial structures, patient positioning at the slit lamp, and changes in breathing patterns while masked.

Key Takeaways:

• Average IOP ranged from 14.7 mm Hg (surgical mask) to 15.1 mm Hg (no mask/KN95) — no statistically significant difference
• 34% of patients had ≥3 mm Hg difference between mask scenarios at the individual level
• Clinicians should consider measuring IOP without a mask or using a handheld tonometer as a backup when results are unexpected or a treatment decision hinges on a small pressure difference

Why it matters: Glaucoma management often turns on small IOP changes, so understanding sources of measurement variability is critical. While routine practice doesn't need to change, clinicians should be alert to mask-related variability — especially when a single reading is driving a treatment call.