What causes acute angle-closure glaucoma (AACG)?

Updated: Jun 20, 2019
  • Author: Albert P Lin, MD; Chief Editor: Inci Irak Dersu, MD, MPH  more...
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Answer

Pupillary block is considered to be the most common cause of AAC. Normally, aqueous humor is made by the ciliary body and flows through the pupil to the anterior chamber, where it drains out of the eye through the trabecular meshwork and the Schlemm canal. If contact occurs between the lens and the iris, aqueous humor accumulates behind the pupil, increasing posterior chamber pressure and forcing the peripheral iris to shift forward. The forward movement of the iris does not cause angle closure in individuals with normal anatomy.

The trabecular meshwork is located between the iris and cornea, and the two structures form an angle that is normally 40°. Persons with susceptible anatomy have a narrow occludable angle, usually of less than 20°. When the iris is pushed forward by the aqueous humor in a narrow occludable angle, it becomes apposed to the trabecular meshwork. This blockage causes accumulation of aqueous humor in the anterior chamber and an acute rise in IOP.

Not all individuals with narrow occludable angle develop AAC, and mechanisms other than pupillary block play a role in development of AAC.

Plateau iris is a condition in which the iris is inserted more anteriorly into the ciliary body and the periphery of the iris is flat. The angle is narrow owing to the anterior iris insertion, and the flat iris bunches up to obstruct the angle when the eye is dilated. [6, 7]

Several medications have been implicated in causing acute ACC by producing swelling in the ciliary body and forward movement of the iris. Sulfa-derivative medications, including acetazolamide, sulfamethoxazole, and hydrochlorothiazide, and antiepileptic medication topiramate have been reported to cause acute attacks. [8, 9]

Persons of Asian descent have thicker irides, and increased iris thickness is associated with angle closure. [10, 11]

Pupillary dilation normally results in loss of iris volume, but this volume decrease is less in eyes that have had AAC; some of these eyes actually showed an increase in iris volume. [12, 13]

Individuals with hyperopia have smaller eyes, and the diameter of the eye (axial length) is shorter. The intraocular structures are spaced closer together. These patients are more likely to have shallow anterior chambers and narrow occludable angles. [1, 2, 3]

Lens volume increases with age and can decrease the amount of space in the anterior chamber via mass effect. [1, 2, 3]


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