fibers of the lens to relax, allowing the lens–iris interface to move forward. Furthermore, their use results in an increase in the amount of iris–lens contact, thus potentially increasing pupillary block. For these reasons, miotics, especially the cholinesterase inhibitors, may induce or aggravate angle closure. Gonioscopy should be repeated soon after miotic drugs are administered to patients with narrow angles.

Because of their potential for precipitating angle closure in susceptible individuals, a number of systemic medications that possess adrenergic (sympathomimetic) or anticholinergic (parasympatholytic) activity carry warnings against use by patients with glaucoma; these include allergy and cold medications, antidepressants, and some urological drugs. Although systemic administration generally does not raise intraocular drug levels to the same degree as does topical administration, even slight mydriasis in a patient with a critically narrow chamber angle can induce angle closure. When such drugs are administered to patients with potentially occludable angles, the ophthalmologist should consider informing the patients of this risk and performing iridotomy.

Dapiprazole and thymoxamine are α-receptor blockers that reverse pharmacologic dilation more rapidly than does placebo. Although the use of dapiprazole following pupillary dilation does not eliminate the possibility of precipitating angle closure, it does reduce the overall time that the pupil is dilated, as well as the critical period when the pupil is mid-dilated. Dapiprazole is no longer available in the United States.

Foster PJ, Devereux JG, Alsbirk PH, et al. Detection of gonioscopically occludable angles and primary angle-closure glaucoma by estimation of limbal chamber depth in Asians: modified grading scheme. Br J Ophthalmol. 2000;84(2):186–192.

Plateau Iris

Plateau iris represents an atypical configuration of the anterior chamber angle that may result in acute or chronic ACG. Angle closure in plateau iris is most often caused by anteriorly positioned ciliary processes that critically narrow the anterior chamber recess by pushing the peripheral iris forward. More recent evidence suggests that plateau iris configuration may result from a more anterior junction of the iris dilator muscle and the ciliary epithelium, which causes the iris root to be more articulated. A component of pupillary block is often present. The angle may be further compromised following dilation of the pupil as the peripheral iris bunches up and obstructs the trabecular meshwork. Plateau iris may be suspected if the central anterior chamber appears to be of normal depth and the iris plane appears to be rather flat for an eye with angle closure. This suspicion can be confirmed with gonioscopy or by the presence of the “double hump” sign on ultrasound biomicroscopy. The diagnosis of plateau iris can only be made by gonioscopy or another technique for imaging the angle. The condition will be missed if the examiner relies solely on the slit-lamp examination or the Van Herick method of angle examination.