This is the abbreviation for Laser Peripheral Iridotomy, a laser procedure performed on people who are at risk for having an acute glaucoma attack. To understand the purpose behind this procedure, it can be useful to think of the eye like a kitchen sink full of water. There is a “faucet” running at all times inside the eye that produces aqueous fluid. This fluid keeps the eye inflated like a water balloon and working properly. There is also a “drain” in the eye called the trabecular meshwork where the aqueous fluid drains away. It is the balance of this fluid input and output that determines the eye’s pressure. The eye’s drain is located in a 360-degree ring at the intersection of the iris (colored part of the eye) with the sclera (the white part of the eye). This intersection is commonly called the “angle” because it is a rather tight intersection with little excess room. Some people’s ocular anatomy is such that their drainage angle is extremely tight and narrow. Under most situations, aqueous fluid can still drain out this tight junction … but if conditions are just right, the drainage angle may shut closed entirely. With the drainage pathway blocked, the eye pressure will shoot up and cause intense pain with vision loss from acute glaucoma. This is always a bad situation … most people come into the office bent over and throwing up from the pain. Even with prompt treatment there is usually some permanent vision loss. For people who appear to have narrow angles, a prophylactic LPI is sometimes recommended. With this procedure a laser is used to create a small hole through the iris. This helps equalize the pressures inside the eye and dramatically decreases the chance of having an acute glaucoma episode. The laser procedure is quick, and for the most part harmless, though there are a couple of risks to be aware of. The main one is visual side effects afterwards. By creating a hole in the iris, this creates a secondary pupil that light can pass through to reach the retina. Some people complain of a ghost image or line around lights at night. This is rare, and we strive to keep the LPI hole very small and up under the eyelid to minimize this possibility. This must be considered and weighed against the possibility of a potentially blinding glaucoma attack.