LPI attempts to “open” a “narrow” angle. Since the angle is the part of the eye that drains fluid FROM the eye, narrowing of the angle can put the eye at risk for an acute attack of angle closure glaucoma. During the LPI, a laser is used to make a small opening in the peripheral iris (the coloured part of the eye). This changes the fluid dynamics in the eye and “opens” the angle. If a patient already has acute angle closure glaucoma, the small opening that is made in the peripheral iris allows fluid to drain more normally and also lowers the eye pressure.