[citation needed] Goldmann applanation tonometry (GAT) is considered to be the gold standard IOP test and is the most widely accepted method.

The force applied to the tonometer head is then adjusted using a dial connected to a variable tension spring until the inner edges of the green semicircles in the viewfinder meet.

[9] The probe is placed on the pre-corneal tear film on the central cornea (see gallery) and the integrated piezoresistive pressure sensor automatically begins to acquire data, measuring IOP 100 times per second.

Rebound tonometers determine intraocular pressure by bouncing a small plastic tipped metal probe against the cornea.

As the probe bounces against the cornea and back into the device, it creates an induction current from which the intraocular pressure is calculated.

Filtered air is pumped into the piston and travels through a small (5 mm (0.20 in) diameter) fenestrated membrane at one end.

The Diaton non-corneal tonometer calculates pressure by measuring the response of a free-falling rod, as it rebounds against the tarsal plate of the eyelid through the sclera.

[15] Non-corneal and transpalpebral tonometry does not involve contact with the cornea and does not require topical anesthetic during routine use.

Transpalpebral tonometry may be useful for measuring postsurgery IOP after myopic LASIK ablation because this technique is not influenced by the treatment.

[citation needed] The ocular response analyser (ORA) is a non-contact (air puff) tonometer that does not require topical anaesthesia and provides additional information on the biomechanical properties of the cornea.

The difference between the pressures at which the cornea flattens inward and outward is measured by the machine and termed corneal hysteresis (CH).

It was firmly evident that due to significantly low positive or negligible correlation, none of these 2 non-contact tonometers can replace the GAT.

[21] Palpation (also known as digital tonometry) is the method of estimating intraocular pressure by gently pressing the index finger against the cornea of a closed eye.