The Goldmann tonometer is a medical instrument used to measure intraocular pressure (IOP) in the eye. It is commonly employed in ophthalmology to help diagnose and monitor conditions like glaucoma. The device works by applying a small amount of pressure to the cornea and measuring the resistance to that pressure. This tonometer consists of a slit lamp and a special prism that makes contact with the eye. The measurement is taken while the patient is seated, and the results help eye care professionals assess the health of the optic nerve and overall eye condition.