This is a very serious disease of the eye, the nature of which is not thoroughly well understood. The eyeball becomes very hard in consequence of an increase of its fluid contents, the result of which is paralysis of the optic nerve in consequence of the severe pressure. When acute, it is generally very painful. The pain is generally accompanied by flashes of light, appearances of rainbow colors, and dimness of vision. The disease should not be mistaken for neuralgia, as it requires very prompt treatment at the hands of a skillful surgeon. It is usually necessary to perform the operation known as iridectomy.