Mask-induced Artifact Impacts Intraocular Pressure Measurement Using Goldmann Applanation Tonometry

The coronavirus (COVID-19) pandemic has impacted ophthalmology practices significantly. American Academy of Ophthalmology and Center for Disease Control guidelines suggest mandatory masking of patients and physicians during outpatient visits. We have recently become aware of a mask-induced phenomenon, whereby the intraocular pressure (IOP) as measured by Goldmann applanation tonometry (GAT) is artificially elevated due to mechanical interference from the mask.

A 37-year-old male with a history of primary open-angle glaucoma on triple therapy presented for a routine visit.

When measuring IOP by GAT the right eye measured 16 mm Hg, but the left eye measured 20 mm Hg. The patient's mask was noted to be touching the base of the sensor rod on the tonometer. This patient's IOP was falsely elevated due to the lateral edge of his mask touching the base of the applanation tonometer, changing the relationship between the bi-prism tip and the weighted balance below, and eliminating the weighted balance from the pressure measuring mechanism. The patient's mask was adjusted to ensure there was no touch and repeat measurement showed an IOP of 16 mm Hg in the left eye.

Recognizing mask-induced alteration in IOP is essential as it could lead to unnecessary escalation of treatment. We recommend flattening the area of mask protrusion during applanation and ensuring that the sensor arm remains clear of the mask while the tonometer tip approaches the cornea, especially at the moment the mires become visible during corneal contact.