What effect does a thick cornea have on intraocular pressure (IOP) readings?

A thick cornea typically leads to an overestimation of intraocular pressure (IOP) readings when using most tonometry techniques, particularly applanation tonometry. This is primarily because the measurement obtained with tonometry is affected by the biomechanical properties of the cornea.

When a tonometer applies force to flatten a portion of the cornea to measure pressure, a thicker and stiffer cornea will resist flattening more than a thinner cornea. As a result of this resistance, the instrument can record a higher pressure than what might be present in the eye. Essentially, the relationship between corneal thickness and IOP readings is non-linear; therefore, individuals with a thicker cornea may appear to have a higher IOP than they actually do, leading to the potential for misdiagnosis of conditions such as glaucoma.

This understanding is crucial for eye care professionals when interpreting tonometry results, as they must consider corneal thickness alongside other factors to accurately assess a patient's true IOP and ocular health.