Final answer:
A tonometer is used to measure intraocular pressure, which is the fluid pressure within the eye. It is an important measurement for diagnosing and monitoring conditions such as glaucoma.
Step-by-step explanation:
The instrument used to measure intraocular pressure is a tonometer.
Intraocular pressure is the fluid pressure within the eye. It is measured to diagnose and monitor conditions such as glaucoma.
A tonometer measures intraocular pressure by exerting force on the eye and observing its response. There are different types of tonometers, including applanation tonometers, which use a small probe to flatten a part of the cornea, and non-contact tonometers, which use a puff of air to measure the force needed to indent the eye.