A pachymeter is a device that uses ultrasound to determine the thickness of the cornea (the clear tissue in front of the coloured iris). Pachymetry is an essential measurement prior to certain refractive surgical procedures, such as LASIK.

Procedures such as LASIK remove tissue from the cornea and, therefore, pachymetry is important to be certain that the cornea will retain a safe amount of central tissue thickness.

A measure of corneal thickness is also important when measuring the pressure inside the eye. If corneal thickness measurements are thicker or thinner than average the intraocular pressure may be overestimated or underestimated. This is very important when following or testing for glaucoma