It’s used to measure intraocular pressure (IOP). (Normal IOP: 10 to 21 mm of Hg)
There are several types of tonometers, including:
1. Indentation tonometer
2. Applanation tonometer
3. Non-contact tonometer (Air puff tonometer)
1. Indentation tonometer-
Measures how much the cornea indents with a known weight.
Figure- Schizont tonometer
2. Applanation tonometer-
These measure the force required to flatten a constant area of the cornea. The Goldmann applanation tonometer is the most widely used type.
Figure- Goldmann applanation tonometer (based on the Imbert-Fick principle)
3. Non-contact tonometer (Air puff tonometer)-
Uses a puff of air to measure IOP without touching the eye.