This is the eye exam technique used to examine the drainage angle inside the eye, and is used to evaluate for glaucoma. The front part of the eye is filled with a fluid called the aqueous humor. This fluid nourishes many structures inside the eye and the balance of aqueous production and drainage is what controls the overall pressure of the eye. The aqueous “drain” is called the trabecular meshwork and is located in a 360-degree ring … right at the point where the iris (the colored part of the eye) intersects with the sclera (the white of the eye). This drainage intersection is also known as the “angle” because of the insertion anatomy. Some people are at risk for their angle to narrow and close, leading to complete blockage of the drain which causes an acute glaucoma. It is useful for an eye doctor to examine this angle in order to let their patients know their risk for having one of these glaucoma attacks. Unfortunately, the angle is a little difficult to see, even with a microscope, because of its interior location. Gonioscopy is the technique where a special lens containing mirrors (a goniolens) is placed onto the surface of the eye. The doctor then looks through this lens/mirror device to see how “open” the angle appears. If the angle seems very tight, the risk of an acute glaucoma attack is high, and a prophylactic LPI laser procedure can be performed to decrease this risk.