Our eyes constantly make aqueous humor. As new aqueous flows into your eye, about the same amount should leave the eye through the drainage angle. This process keeps pressure in your eye (called intraocular pressure or IOP) stable. If the drainage angle is not working properly, fluid builds up. Pressure in the eye rises, damaging the optic nerve. This is often how glaucoma develops.
Your ophthalmologist will perform a gonioscopy if certain conditions are found during your eye exam. Most commonly, gonioscopy is done to check for signs of glaucoma. The exam can show if your drainage angle is too narrow for fluid to drain properly, or if it is blocked by part of the iris.
In other cases, gonioscopy may be done when there are signs of uveitis, eye trauma, tumors or other conditions.