What is the definition or description of: gonioscopy?

A glaucoma test: Gonioscopy is a procedure done during an eye exam where a hand held goniolens is placed on the surface of the eye (using eye drop anesthetic) and the eye is examined with the slit lamp. This is to examine the iridocorneal angle, which is where the cornea meets the iris internally. This area is where fluid drains from the eye. This test is used to distinguish open angle from closed angle glaucoma.