Applanation tonometer

Applanation Tonometer is a medical instrument used primarily by ophthalmologists and optometrists for measuring the intraocular pressure (IOP) inside the eye. This measurement is crucial in the diagnosis and management of glaucoma, a group of eye diseases that can lead to blindness if left untreated.

History

The concept of applanation tonometry was first introduced by Hans Goldmann in the 1950s. The Goldmann applanation tonometer is considered the gold standard in IOP measurement and is widely used in clinical practice.

Principle

Applanation tonometry works on the principle of Imbert-Fick law, which states that the pressure in a perfectly flexible and dry sphere can be measured by applanating or flattening its surface. However, the human eye is not a perfect sphere and is not perfectly flexible, so certain corrections are applied in the measurement.

Types

There are several types of applanation tonometers, including the Goldmann applanation tonometer, the Perkins tonometer, and the non-contact or "air puff" tonometer. Each type has its own advantages and disadvantages, and the choice of tonometer depends on the patient's condition and the clinician's preference.

Procedure

The procedure for applanation tonometry involves numbing the eye with a topical anesthetic, then applying a small amount of dye to the eye. The tonometer is then brought into contact with the cornea, and the pressure required to flatten a certain area of the cornea is measured.

Accuracy and Limitations

While applanation tonometry is generally considered accurate and reliable, it has some limitations. It can be affected by corneal thickness and rigidity, and it may not be suitable for patients with certain corneal conditions. Other methods of IOP measurement, such as dynamic contour tonometry and ocular response analyzer, may be used in these cases.

See Also

• Ophthalmology
• Glaucoma
• Intraocular pressure
• Goldmann applanation tonometer
• Dynamic contour tonometry
• Ocular response analyzer