Tonometry is used to measure intraocular pressure. There are two main types: indentation and applanation. Indentation tonometry includes the Schiotz tonometer. Applanation tonometry includes Goldmann, Perkins, pneumatic, and air-puff techniques. The Goldmann tonometer is considered the gold standard but requires a slit lamp. The Perkins and Tono-Pen are handheld applanation devices. Pneumatic tonometry uses a pressure transducer while air-puff is non-contact. Accuracy varies between techniques.
Tonometry is used to measure intraocular pressure. There are two main types: indentation and applanation. Indentation tonometry includes the Schiotz tonometer. Applanation tonometry includes Goldmann, Perkins, pneumatic, and air-puff techniques. The Goldmann tonometer is considered the gold standard but requires a slit lamp. The Perkins and Tono-Pen are handheld applanation devices. Pneumatic tonometry uses a pressure transducer while air-puff is non-contact. Accuracy varies between techniques.
Tonometry is used to measure intraocular pressure. There are two main types: indentation and applanation. Indentation tonometry includes the Schiotz tonometer. Applanation tonometry includes Goldmann, Perkins, pneumatic, and air-puff techniques. The Goldmann tonometer is considered the gold standard but requires a slit lamp. The Perkins and Tono-Pen are handheld applanation devices. Pneumatic tonometry uses a pressure transducer while air-puff is non-contact. Accuracy varies between techniques.
Tonometry is used to measure intraocular pressure. There are two main types: indentation and applanation. Indentation tonometry includes the Schiotz tonometer. Applanation tonometry includes Goldmann, Perkins, pneumatic, and air-puff techniques. The Goldmann tonometer is considered the gold standard but requires a slit lamp. The Perkins and Tono-Pen are handheld applanation devices. Pneumatic tonometry uses a pressure transducer while air-puff is non-contact. Accuracy varies between techniques.
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TONOMETRY
TONOMETRY • Tonometry is the procedure performed to determine the intraocular pressure (IOP). CLASSIFICATION TONOMETRY
DIRECT INDIRECT
Indentation Applanation Manometer
APPLANATION
Contact Non-contact
Goldmann Perkins Air-puff Pulse air
INDENTATION TONOMETER
•It is based on fundamental fact that plunger
will indent a soft eye more than hard eye. •The indentation tonometer in current use is that of Schiotz . •It was devised in 1905 and continued to refine it through 1927. PROCEDURE Patient should be anaesthetising with 4% lignocaine or 0.5% proparacaine. with the patient in supine position, looking up at a fixation target while examiners separates the lids and lower the tonometer plate to rest on the cornea so that plunger is free to move. The 5.5gm weight is initially used. If the scale reading is 4 or less , additional weight is added. ADVANTAGES •Simple Technique •Elegant design •Portable •No need for slit lamp or power supply •Reasonably priced •Widely used tonometer Applanation tonometers • Goldman tonometer • Perkins applanation tonometer • Pneumatic tonometer • Tono pen Goldmann tonometry • The concept was introduced by goldmann in 1954 • It is based on IMBERT FICK LAW • It states that the pressure inside an ideal sphere (P) is equal to force (F) required to flatten(A) • P=F/A Cont… • Most popular and accurate tonometer. • It consists of double prism mounted on slit lamp. • The prism applanates the cornea in an area of 3.06 mm diameter. Techniqu e • Topical anesthesia • Staining tear film with fluorescein. • The cornea and biprisms are illuminated with cobalt blue light. • Biprism just touches the apex of cornea. • At this point two fluorescent semicircles are viewed through prism. • Applanation force against cornea is adjusted until inner edges of two semicircles just touches. Potential errors
Patient related • Thin cornea • Thick cornea • Astigmatism • Irregular cornea Technical • Tonometer out of calibration • Repeated tonometry • Pressing on the eyelids or globe • Squeezing of the eyelids Advantage • s Highly accurate • Do not requires supine position • portable Disadvantages • Not portable • costly • reading error if scares on cornea Perkins Tonometer • It uses the same biprism as the Goldmann applanation. • The light source is powered by battery. • The readings are consistent and compared quite well with the Goldmann applanation. Perkins Tonometer Perkins – • Handheld • Horizontal as well as vertical • Infants, children, recumbent patients Advantage s • Portable • Does not requires electricity
Disadvantage • It requires supine position • Costly Pneumatic tonometer • Cornea is applanated by touching apex by silastic diaphragm covering sensing nozzle. • It is connected to central chamber containing pressurized air. • There is pneumatic to electronic transducer. • It converts the air pressure to recording on paper strip and IOP is red. Pneumatic tonometer Tono •Thispen is handheld Mackay Marg type tonometer It is a computerised pocket tonometer •It converts IOP into electric waves Cont… • The wave form is internally analyzed by a microprocessor. • Three to six estimations of the pressure are then averaged. • The instrument is 18 cm in length and weighs 60 g. NON-CONTACT TYPE
• Air puff tonometer :- In this central part of
cornea is flattened by a jet of air . This tonometer is very good for mass screening as there is no danger of cross infection and local anaesthetic is not required. • Pulse air tonometer :- It is a non-contact tonometer that can be used with the patient in any position.
