Table 1.

Summary of the characteristics of the various available tonometers.

Tonometer Type	Production Year	Working Principle	Contact/ Noncontact	Advantages	Disadvantages	Clinical Suitability	Cost *
Schioetz tonometer	1905	indentation	contact	Simple	High variability	still used only in developing countries	feasible
				Inexpensive	Can be used in a supine position only
				No need of slit-lam, electricity or charging batteries	Affected by various sources of error
					Topical anesthesia is needed
Goldmann applanation tonometer (GAT)	1955	applanation	contact	Quite simple to use	Affected by corneal thickness and other corneal parameters	good	feasible
				Accurate and reproducible measurements	The accuracy depends on the clinician’s experience
				It is currently considered as the gold standard in IOP measurement	Needs to be used with a slit-lamp
					Can be used in the upright position only
					Topical anesthesia and fluorescein are needed
Perkins tonometer	1965	applanation	contact	Can be used in a supine position too	Affected by corneal thickness and other corneal parameters	good	feasible
					Topical anesthesia and fluorescein are needed
TonoPen	1989	indentation/ applanation	contact	Lightweight and portable	Hight variability and quite poor repeatability	moderate	feasible
				Quick and simple to use	Can underestimate IOP values
				Can be used in any position	Topical anesthesia is needed
				No need of slit-lamp or electricity	Influenced by corneal parameters
				Self-calibration, provides quality index
Air-puff tonometers	1973	applanation	noncontact	Easy and fast to use	Need of regular calibration	ideal as a screening tool	medium
				No need to touch the cornea	Readings are device-dependent
				No need of topical anesthesia and fluorescein	Possible germs aerosol
				Can be used by paramedical staff	Influenced by corneal parameters
					Less accurate when IOP > 20 mmHg
Ocular Response Analyzer	2005	applanation	noncontact	Simple to use, self-calibration, provides quality index	Possible germs aerosol	good	expensive
				No need of topical anesthesia and fluorescein
				Can be used by paramedical staff
				Provides additional information (corneal central thickness and biomechanics)
				IOP correction for corneal biomechanical parameters
				Useful after corneal refractive surgery
				Detection of corneal diseases
Corvis ST	2011	indentation/ applanation	noncontact	Simple to use, self-calibration, provides quality index	Tends to underestimate the GAT IOP values	good	expensive
				No need of fluorescein and topical anesthesia
				Can be used by paramedical staff
				Provides additional information (corneal central thickness and biomechanics)
				IOP correction for corneal biomechanical parameters
				Useful after corneal refractive surgery
				Detection of corneal diseases
Pneumotonometers	1969	applanation	contact	OBF provides information on the ocular blood pulse	Affected by corneal thickness	controversial	expensive
					Overestimates IOP values
iCare tonometer	1997	ballistic probe (rebound)	contact	Ease of use with a short learning curve	Needs a proper central positioning of the tip	excellent	feasible
				Portable and self-calibrated	Influenced by corneal thickness
				No slit-lamp or topical anesthesia or fluorescein dye required
				Can be used by trained non-medical staff
				Can be used in supine positions (iCare PRO and iCare 200)
				Minimal corneal trauma (useful in post-operative patients)
				The home version can be useful in self-twenty-four-hour monitoring of IOP
Dynamic contour tonometer (DCT, PASCAL)	2005	contour matching	contact	No need of fluorescein, disposable probes	Need of slit lamp and topical anesthesia	poor	medium
				Self-calibration, provides quality index	Difficult to use
				Independent from corneal properties	Need of highly cooperative patients
				Useful after corneal refractive surgery
				High precision
				Additional information (ocular pulse amplitude)
BioResonator ART	2003	applanation	contact	No need of fluorescein	Need of slitlamp and local anesthetic	moderate	medium
				Self-calibration, provides quality index	Need of probe disinfection
				High reliability (median of repeated IOP measurements)	Required training to use
					Affected by corneal properties
Sensimed Triggerfish	2004	corneal curvature monitoring	contact	Continuous measurements over a 24-hour period	It does not provide direct IOP values	moderate	feasible
				Good tolerability	IOP estimation accuracy not known
				High reproducibility

* feasible: 0–5000 euros; medium range 5000–10,000 euros; expensive: >10,000 euros.