In music, a tonometer is an instrument used to determine the pitch or vibration rate of tones, such as a tuning fork.

Tonometry is the measurement of tension or pressureA tonometer is an instrument for measuring tension or pressure[http://www.mercksource.org/pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_t_13zPzhtm.

In ophthalmology, tonometry is the procedure eye care professionals perform use to determine the intraocular pressure (IOP), the pressure found inside the eye. It is an important test in the evaluation of ocular conditions such as glaucoma as well conditions such as phthisis bulbi, and iritis. Most tonometers are calibrated to measure pressure in mmHg.

Methods of ophthalmotonometry

• Applanation tonometry measures intraocular pressure either by the force required to flatten a constant area of the cornea (e.g. Goldmann tonometry) or by the area flattened by a constant force.Cline D; Hofstetter HW; Griffin JR. Dictionary of Visual Science. 4th ed. Butterworth-Heinemann, Boston 1997. ISBN 0-7506-9895-0

• Goldmann tonometry is considered to be the gold standard in tonometry as it is the most accurate method of determining intraocular pressure.Amm M, Hedderich J. "tonometry with a digital tonometer in healthy eyes and after penetrating keratoplasty." Ophthalmologe. 2005 Jan;102(1):70-6. PMID 15322801.Schlote T, Landenberger H. "pressure difference in Goldmann applanation tonometry versus a transpalpebral tonometer TGDc-01'PRA' in glaucoma patients." Klin Monatsbl Augenheilkd. 2005 Feb;222(2):123-31. PMID 15719316. Applanation tonometry uses a special calibrated sterile probe attached to a slit lamp biomicroscope to flatten part of the cornea. Because the probe makes contact with the cornea, a topical anesthetic, such as oxybuprocaine, tetracaine, alcaine, proxymetacaine or proparacaine is introduced onto the surface of the eye in the form of one or a few eye drops. A yellow fluorescein dye is used in conjuction with a cobalt blue filter to aid the examiner in determining the IOP.

• MacKay Marg

• Pneumotonometry, also known as non-contact tonometry or air-puff tonometry, uses an instrument that senses deflections of the cornea in reaction to a puff of pressurized air.^* Although not considered to be the most accurate way to measure IOP, it is often used as a simple way to screen for high IOP. It is an easy way to test children.

• Electronic indentation tonometry. The Tono-Pen is a portable electronic, digital pen-like instrument that determines IOP by making contact with the cornea, afer use of topical anesthetic eye drops. This is especially useful for very young children, patients unable to reach a slit lamp due to disability, or patients who are uncooperative during applanation tonometry.

• Impression tonometry, also known as identation tonometry, measures the depth of the impression produced by a small plunger carrying a known weight. Intraocular pressure is determined by assessing the movement of the plunger to a calibrated scale.

Schiotz tonometry is a type of impression tonometery, historically was used to determine IOP. This type of tonometry makes use of a plunger to indent the cornea. The IOP is determined with small metal weights.

• Transpalpebral (Diaton) tonometry measures intraocular pressure through the eyelid. It is regarded as a simple and safe method of ophthalmotonometry. Transpalpebral tonometry requires no contact with the cornea, therefore sterilization of the device and topical anesthetic drops are not required and there is very little risk of infection. Compared with the current standard of Goldmann applanation tonometry, recent data suggests that transpalpebral tonometry via the Diaton tonometer is not as accurate in that it has been found to underestimate and show more variability in intraocular pressure values.Troost A, Specht K, Krummenauer F, Yun SH, Schwenn O. "Deviations between transpalpebral tonometry using TGDc-01 and Goldmann applanation tonometry depending on the IOP level." Graefes Arch Clin Exp Ophthalmol. 2005 Sep;243(9):853-8. Epub 2005 Mar 15. PMID 16158308. van der Jagt LH, Jansonius NM. "Three portable tonometers, the TGDc-01, the ICARE and the Tonopen XL, compared with each other and with Goldmann applanation tonometry*." Ophthalmic Physiol Opt. 2005 Sep;25(5):429-35. PMID 16101949. Losch A, Scheuerle A, Rupp V, Auffarth G, Becker M. "Transpalpebral measurement of intraocular pressure using the TGDc-01 tonometer versus standard Goldmann applanation tonometry." Graefes Arch Clin Exp Ophthalmol. 2005 Apr;243(4):313-6. Epub 2004 Oct 15. PMID 15864620. Lam AK, Lam CH, Chan R. "The validity of a digital eyelid tonometer (TGDc-01) and its comparison with Goldmann applanation tonometry - a pilot study." Ophthalmic Physiol Opt. 2005 May;25(3):205-10. PMID 15854065. Although not advised for the clinical management of those with glaucoma , transpalpebral tonometery has been described as sufficient for clinical use and it may have applications in the home-monitoring of intraocular pressures.Nesterov AP, Piletskii GK, Piletskii NG. "tonometer for measuring intraocular pressure." Vestn Oftalmol. 2003 Jan-Feb;119(1):3-5. PMID 12608032. Use of transpalpebral tonometry may be indicated in those for whom Goldmann tonometry is not indicatedSandner D, Bohm A, Kostov S, Pillunat L. "Measurement of the intraocular pressure with the 'transpalpebral tonometer' TGDc-01 in comparison with applanation tonometry." Graefes Arch Clin Exp Ophthalmol. 2005 Jun;243(6):563-9. Epub 2004 Dec 22. PMID 15614540., such as in children, those with corneal pathology, or those who have had corneal surgery.Troost A, Yun SH, Specht K, Krummenauer F, Schwenn O. "Transpalpebral tonometry: reliability and comparison with Goldmann applanation tonometry and palpation in healthy volunteers." Br J Ophthalmol. 2005 Mar;89(3):280-3. PMID 15722303.

• Palpation, also known as digital tonometry, to measure intraocular pressure is performed by gently pressing the fingertips of both index fingers onto the upper part of the bulbus through the eyelid.

• Dynamic contour tonometry

References

External links

• Tonometry - WebMD
• Tonometry - The Johns Hopkins Consumer Guide to Medical Tests
• Kirstein, E. "An Update on Methods for Assessing Intraocular Pressure." Retrieved June 7, 2006.
• Tonometry- Transpalpebral Diaton Tonometry

Medical equipment | Ophthalmology

Tonometría