What is the term for the tonometry technique that displaces a minimal amount of fluid?

The term that describes the tonometry technique which displaces a minimal amount of fluid is known as applanation tonometry. This method involves flattening a small area of the cornea to measure intraocular pressure (IOP). During the applanation process, the pressure required to flatten the cornea correlates with the internal eye pressure; thus, it is a direct measurement technique.

In applanation tonometry, a known force (usually from a small tonometer or a probe) is applied to the surface of the cornea, and the amount of force necessary to achieve a specific degree of flattening is measured. Since this technique targets only a small area of the cornea, it minimally displaces fluid within the eye, consequently providing a reliable measurement of intraocular pressure while maintaining the natural state of the eye as much as possible.

Other techniques, like non-contact tonometry, utilize a puff of air to measure pressure and may displace more fluid as the air interacts with the eye. Rebound tonometry also employs a small probe that bounces off the cornea, potentially altering fluid dynamics more than applanation. Pneumatic tonometry uses a pressurized system to measure IOP, which is less focused on minimizing fluid displacement compared to applanation