Gonioscopy is a type of eye examination performed to check the internal structures of the eyes. Its goal is to thoroughly evaluate eye health and properly diagnose eye diseases such as glaucoma, which is the second leading cause of blindness. The eye exam evaluates the internal drainage system of the eye, also referred to as the anterior chamber angle. The "angle" is where the cornea and the iris meet. This is the location where fluid inside the eye (aqueous humor) drains out of the eye and into the venous system. 

Under normal circumstances, the angle cannot be seen on examination. A special contact lens prism placed on the surface of the eye, allows visualization of the angle and drainage system. By looking at the "angle," physicians can determine if it is open or closed as well as if there are abnormal blood vessels, adhesions (synechiae), or damage from previous eye trauma. In addition, gonioscopy allows the eye doctor to note more subtle characteristics of the eye’s drainage system, in order to guide his or her diagnosis and treatment plan