Angle closure refers to an anatomic configuration in which there is mechanical blockage of the trabecular meshwork by the peripheral iris. Anatomic alterations in anterior segment structures result in obstruction of the iridocorneal drainage angle through apposition (iridotrabecular contact) or consequent to the formation of peripheral anterior synechiae (PAS; adhesions of the peripheral iris to the trabecular meshwork). The term angle-closure disease refers to the presence of PAS, ocular hypertension associated with angle closure, acute primary angle closure, or glaucomatous optic neuropathy attributable to primary angle closure.
Angle closure is divided into 2 main categories—(1) primary angle closure and (2) secondary angle closure—according to the etiology of the disease. In primary angle closure, no secondary pathologic condition can be identified; there is only an anatomic predisposition. In secondary angle closure, an identifiable pathologic cause—such as an intumescent lens, iris neovascularization, chronic inflammation, corneal endothelial migration into the angle, or epithelial ingrowth—initiates the angle closure. See Chapter 10 in this volume for discussion of secondary angle closure.
Table 9-1 European Glaucoma Society Classification of Angle Closure
Current nomenclature further classifies eyes on the primary angle-closure spectrum into 3 categories based on the severity of the condition:
primary angle-closure suspect (PACS), in which the eye has an anatomic configuration that increases the risk of developing angle-closure disease
primary angle closure (PAC), in which trabecular meshwork damage or dysfunction is already present, characterized by PAS or elevated intraocular pressure (IOP)
primary angle-closure glaucoma (PACG), which is characterized by PAS or elevated IOP and glaucomatous optic neuropathy (Table 9-1)
Worldwide prevalence of angle-closure glaucoma (ACG) is estimated to reach over 23 million in 2020 and over 32 million in 2040. ACG is more common in females and in certain ethnic groups, such as particular Asian populations and the Inuit. Prevalence rates in European and African populations are generally lower, but genetic heterogeneity can result in widely varying prevalence within populations of the same continent. ACG has been estimated to account for over 90% of blindness due to glaucoma in the Chinese population.
The angle-closure–related disorders are a diverse group of diseases. Although the various forms of angle closure are united by the presence of PAS and/or iridotrabecular apposition, different mechanisms are responsible for these features. Moreover, the clinical presentation of angle closure varies from the abrupt and dramatic onset of acute angle closure to the insidious and asymptomatic presentation of chronic disease.
To initiate the appropriate therapy, the physician must identify the anatomic changes in the angle and the underlying pathophysiology that has precipitated the disease. Early diagnosis and treatment of most forms of angle closure or narrowing can be invaluable and sometimes curative. Screening patients at greatest risk for angle closure can be beneficial in reducing both the number of patients who develop these diseases and the risk of blindness.
American Academy of Ophthalmology Glaucoma Panel. Preferred Practice Pattern® Guidelines. Primary Angle Closure. American Academy of Ophthalmology; 2016. www.aao.org/ppp
Chan EW, Li X, Tham YC, et al. Glaucoma in Asia: regional prevalence variations and future projections. Br J Ophthalmol. 2016;100(1):78–85.
Tham YC, Li X, Wong TY, Quigley HA, Aung T, Cheng CY. Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis. Ophthalmology. 2014;121(11):2081–2090.
Yip JL, Foster PJ. Ethnic differences in primary angle-closure glaucoma. Curr Opin Ophthalmol. 2006;17(2):175–180.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.