Glaucoma is best detected by examination of the optic disk, since intraocular pressure is not always elevated in patients with the condition. A large, vertically oval cup within the optic disk is strong evidence for glaucoma. Open-angle glaucoma, the most common form of the disorder, often is not detected until the disease is advanced. It can usually be treated successfully with topical medications, but systemic absorption of these can result in serious side effects. If medical treatment fails, laser therapy or filtering surgery may be helpful. Acute angle-closure glaucoma has a sudden onset marked by alarming elevations in intraocular pressure. It is treated immediately with topical pilocarpine and systemic osmotic agents, and an iridectomy should be performed as soon as possible. Congenital glaucoma can be cured with goniotomy.