Angle-closure glaucoma involves a disruption in the drainage of the aqueous humor. This fluid builds up behind the iris, pushing it forward and causing a very painful increase in intraocular pressure and a severe deterioration in vision. Prompt treatment is necessary to prevent permanent vision loss. In these cases, a special laser and specific contact lenses are used to create a microscopic opening in the iris (LIT, laser iridotomy), through which the accumulated aqueous humor can drain. This leads to a rapid improvement in pain and eye pressure.