Lens dislocation/subluxation may be caused by trauma, pseudoexfoliation syndrome, or congenital zonular dysgenesis (e.g., Marfan syndrome, spherophakia). Mechanisms for glaucoma in dislocated/subluxed lenses include an inflammatory reaction caused by the lens material itself, pupillary block, or damage to the anterior chamber angle sustained during trauma. A dislocated lens may become hypermature and cause a phacolytic glaucoma (see 9.12.1, PHACOLYTIC GLAUCOMA). In addition, a dislocated or subluxed lens can lead to sensitization of lens proteins if associated with capsule violation (see 9.12.3, PHACOANTIGENIC GLAUCOMA [FORMERLY PHACOANAPHYLAXIS]). Pupillary block is the most common mechanism and can occur secondary to anterior displacement of the lens or vitreous plugging the pupil. Treatment is aimed at relieving the pupillary block. Iridectomy is usually indicated and necessary to prevent future attacks. Cycloplegics are helpful along with face up/supine head positioning to allow lens to fall back. IOP-lowering medications are employed. Avoid miotics. Surgical lens removal often needed, occasionally through a pars plana approach. See 13.10, SUBLUXED OR DISLOCATED CRYSTALLINE LENS, for a more in-depth discussion.