Pupillary Block

Pupillary block occurs when the pupillary margin of the iris contacts the anterior surface of the lens. This creates a barrier for the outflow of aqueous humor from the posterior chamber to the anterior chamber and resultant increased pressure in the posterior chamber. This pressure can cause the iris to bulge forward (iris bombe) and occlude the angle, blocking the outflow of aqueous humor through the trabecular meshwork and causing increased intraocular pressure (IOP). This is one of the causes of angle-closure glaucoma. Risk factors for pupillary block and angle-closure glaucoma include shallow anterior chamber, proportionally thick lens, anteriorly located lens-iris diaphragm, and narrow angles. Secondary causes of pupillary block include posterior synechiae from uveitis, ectopia lentis, or enlargement of the lens (i.e., mature cataracts). Pupillary block can also be precipitated by pupillary dilation. Patients with acute pupillary block may report a history of sudden-onset unilateral eye pain, headache, blurred vision, rainbow-colored halos around lights, nausea, and vomiting. Examination may show a fixed mid-dilated pupil, corneal haze, conjunctival injection, elevated IOP, anterior chamber cell and flare, and possible optic nerve head edema. Gonioscopy should be performed to evaluate for occludable angles in the unaffected eye. In the acute setting, the goal of treatment is to lower the IOP quickly using topical, oral, and/or IV medications. Definitive treatment is laser peripheral iridotomy. Lens extraction can also be therapeutic for these patients. Patient with subacute pupillary block may complain of intermittent episodes of similar symptoms. IOP measurement and gonioscopy are important for this evaluation. Chronic pupillary block may mimic open-angle glaucoma with symptoms of peripheral vision loss in the later stages of disease; however, these patients will demonstrate occludable angles on gonioscopy. These patients should be followed regularly to monitor for changes in IOP, optic nerve cupping, and visual field loss.