In ophthalmology, gonioscopy is a routine procedure that measures the angle between the iris and the cornea (the iridocorneal angle), using a goniolens (also known as a gonioscope) together with a slit lamp or operating microscope. Its use is important in diagnosing and monitoring various eye conditions associated with glaucoma.

The goniolens or gonioscope

The goniolens allows the clinician - usually an ophthalmologist or optometrist - to view the irideocorneal angle through a mirror or prism, without which the angle is masked by total internal reflection from the ocular tissue. The mechanism for this process varies with each type of goniolens. Three examples of goniolenses are the: There are many other goniolenses available for use, including modified versions of the aforementioned, which prove valuable for surgical use (goniotomy).

Interpreting the gonioscopic image

Etymology

The word originates from the Greek words γωνία (gōnía, "angle") and σκοπέω (skopéō, "to see"). (As an aside to help you remember, the suffix "-gon" in "polygon" and its relatives comes from the same root word, so "polygon" literally means "many angles".)