This is when the “angle” inside the eye is naturally tight, putting you at risk for having an acute glaucoma attack. The front part of the eye is filled with a fluid called the aqueous humor. This fluid is continuously produced and drained from the eye, with the balance of fluid input and output controlling the overall pressure of the eye. The drain inside the eye is called the trabecular meshwork and it is located where the white of the eye (the sclera) meets the colored iris. The anatomy of this intersection forms an angle. Some people’s ocular anatomy is such that their angle is very narrow. If the angle narrows too much, it can shut down entirely. With no aqueous drainage, the pressure inside the eye shoots up suddenly, causing an acute glaucoma with extreme pain and vision loss. Narrow angles can be evaluated using gonioscopy. If the angles are narrow enough, a prophylactic LPI procedure can be considered to avoid angle closure.