tonometer /to·nom·e·ter/ (to-nom´ĕ-ter) an instrument for measuring tension or pressure, particularly intraocular pressure.
Tonometer
tonometer
air-puff tonometer an instrument for measuring intraocular pressure by sensing deflections of the cornea in reaction to a puff of pressurized air.
applanation tonometer an instrument that measures intraocular pressure by determination of the force necessary to flatten a corneal surface of constant size.
impression tonometer , indentation tonometer an instrument that measures intraocular pressure by direct pressure on the eyeball.
to·nom·e·ter (t -n m  -t r)n. Any of various instruments for measuring pressure or tension, especially one used in tonography. to  no·metric (tn-m trk) adj.to·nom e·try n. |
Tonometer
An instrument that measures intraocular pressure (IOP).
Mentioned in: Eye Examination
tonometer
[tōnom′ətər]
Etymology: Gk, tonos + metron, measure
an instrument used in measuring tension or pressure, especially intraocular pressure.
tonometer
an instrument for measuring tension or pressure, especially intraocular pressure.
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Principles of the tonometer. By permission from Guyton R, Hall JE, Textbook of Medical Physiology, Saunders, 2000
applanation tonometer
measures the force required to flatten or applanate an area of cornea. Includes the MacKay-Marg, Halberg, Dräger and Goldmann tonometers.
indentation tonometer
measures the pressure required to indent the cornea; includes the Schiotz and pneumatonograph.
tonometer
An instrument for estimating intraocular pressure. It measures either the degree of corneal deformation produced by a known force, or the force needed to produce a given degree of corneal deformation. See glaucoma detection; manometer; intraocular pressure; ocular rigidity; Tonopen.
air-puff tonometer See non-contact tonometer.
applanation tonometer A tonometer in which the intraocular pressure is estimated either by the force required to flatten a constant corneal area as, for example, in the Perkins (Fig. T14) and Goldmann (Fig. T15) tonometers, or by the area flattened by a constant force, as, for example, in the Maklakov and Tonomat tonometers. The Goldmann tonometer (Figs. T15 and T16) is used in conjunction with a slit-lamp and provides an accurate reading with which all other tonometers are usually compared. The Perkins tonometer is a handheld instrument. See Imbert-Fick law.
electronic tonometer Any tonometer with an electronic readout. These instruments act swiftly, the procedure usually being completed within a fraction of a second.
Goldmann tonometer See applanation tonometer.
impression tonometer A tonometer in which the intraocular pressure is estimated by the degree of indentation of the cornea. The excursion of the plunger of the tonometer is read from a calibrated scale and converted into values of the intraocular pressure, often using appropriate tables. The most common such instrument is that of Schiötz. Syn. indentation tonometer. See ocular rigidity.
indentation tonometer See impression tonometer.
Mackay-Marg tonometer An electronic tonometer in which a plunger in the centre of a flat footplate which applanates the cornea protrudes by a very small amount (5 mm). The intraocular pressure is related to the counter force required to resist displacement of this plunger when the cornea is flattened by the footplate. The result is read by interpretation of a graph on a strip chart.
Maklakov's tonometer See applanation tonometer.
non-contact tonometer (NCT) A tonometer that does not require any contact to be made between the tonometer and the eye. Hence no anaesthesia is required with this instrument. It consists of sending a puff of air towards the cornea of sufficient strength to flatten a predetermined area of cornea. The time taken from the onset of the puff of air to the applanation of the cornea (which is monitored optically) is recorded electronically and is proportional to the intraocular pressure. A digital readout of pressure, in mmHg, appears within about 15 ms after the measurement is initiated. The same principle is applied in the handheld Pulsair non-contact tonometer and in the Reichert Non-Contact tonometer. Syn. Air-puff tonometer; pneumatic tonometer.
Perkins tonometer See applanation tonometer.
Pulsair non-contact tonometer See non-contact tonometer.
rebound tonometer A handheld, compact, portable tonometer. It incorporates its own battery supply and digital readout. A pair of coils coaxial to a probe shaft is used: a solenoid coil propels a lightweight magnetized probe against the cornea and it bounces back. A sensing coil detects several motion parameters from the voltage that the moving probe induces. They are recorded and analyzed. The intraocular pressure is related to the duration of the corneal impact, the shorter the duration, the higher the pressure. The probe is disposable and its tip is covered with a round plastic cover to minimize corneal damage. The results correlate well with the Goldmann tonometer, although with slightly higher readings.
Reichert Non-Contact tonometer See non-contact tonometer.
Schiötz tonometer See impression tonometer.
Tonomat tonometer See applanation tonometer.
air-puff tonometer See non-contact tonometer.
applanation tonometer A tonometer in which the intraocular pressure is estimated either by the force required to flatten a constant corneal area as, for example, in the Perkins (Fig. T14) and Goldmann (Fig. T15) tonometers, or by the area flattened by a constant force, as, for example, in the Maklakov and Tonomat tonometers. The Goldmann tonometer (Figs. T15 and T16) is used in conjunction with a slit-lamp and provides an accurate reading with which all other tonometers are usually compared. The Perkins tonometer is a handheld instrument. See Imbert-Fick law.
electronic tonometer Any tonometer with an electronic readout. These instruments act swiftly, the procedure usually being completed within a fraction of a second.
Goldmann tonometer See applanation tonometer.
impression tonometer A tonometer in which the intraocular pressure is estimated by the degree of indentation of the cornea. The excursion of the plunger of the tonometer is read from a calibrated scale and converted into values of the intraocular pressure, often using appropriate tables. The most common such instrument is that of Schiötz. Syn. indentation tonometer. See ocular rigidity.
indentation tonometer See impression tonometer.
Mackay-Marg tonometer An electronic tonometer in which a plunger in the centre of a flat footplate which applanates the cornea protrudes by a very small amount (5 mm). The intraocular pressure is related to the counter force required to resist displacement of this plunger when the cornea is flattened by the footplate. The result is read by interpretation of a graph on a strip chart.
Maklakov's tonometer See applanation tonometer.
non-contact tonometer (NCT) A tonometer that does not require any contact to be made between the tonometer and the eye. Hence no anaesthesia is required with this instrument. It consists of sending a puff of air towards the cornea of sufficient strength to flatten a predetermined area of cornea. The time taken from the onset of the puff of air to the applanation of the cornea (which is monitored optically) is recorded electronically and is proportional to the intraocular pressure. A digital readout of pressure, in mmHg, appears within about 15 ms after the measurement is initiated. The same principle is applied in the handheld Pulsair non-contact tonometer and in the Reichert Non-Contact tonometer. Syn. Air-puff tonometer; pneumatic tonometer.
Perkins tonometer See applanation tonometer.
Pulsair non-contact tonometer See non-contact tonometer.
rebound tonometer A handheld, compact, portable tonometer. It incorporates its own battery supply and digital readout. A pair of coils coaxial to a probe shaft is used: a solenoid coil propels a lightweight magnetized probe against the cornea and it bounces back. A sensing coil detects several motion parameters from the voltage that the moving probe induces. They are recorded and analyzed. The intraocular pressure is related to the duration of the corneal impact, the shorter the duration, the higher the pressure. The probe is disposable and its tip is covered with a round plastic cover to minimize corneal damage. The results correlate well with the Goldmann tonometer, although with slightly higher readings.
Reichert Non-Contact tonometer See non-contact tonometer.
Schiötz tonometer See impression tonometer.
Tonomat tonometer See applanation tonometer.
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Fig. T14 Perkins tonometer
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Fig. T15 Goldmann tonometer. The model shown here is fitted with a Tonosafe disposable prism, which comes into contact with the eye; this eliminates the risk of cross-infection
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Fig. T16 Fluorescein pattern seen when the head of the Goldmann applanation tonometer rests against the anterior corneal surface. A, the dial reading is greater than the IOP; B, the dial reading is equal to the IOP and the applanated corneal area has a diameter of 3
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