CHAPTER 5

Angle-Closure Glaucoma

Introduction

Of the nearly 67 million patients with glaucoma worldwide, it has been estimated that one-half are of Asian descent. The prevalence of angle-closure glaucoma (ACG), much of which is primary angle closure, has been shown to be higher than that of other types of glaucoma among Asian persons. Population studies have determined that the ratio of open-angle glaucoma (OAG) to ACG in Chinese individuals ranges from 1:1 to 2.6:1. Primary ACG (PACG) is more common than previously recognized and is a leading cause of bilateral blindness worldwide. For example, PACG is responsible for 91% of the bilateral blindness in China, affecting more than 1.5 million Chinese persons.

In 1920, Curran proposed the mechanism of pupillary block and the importance of an iridectomy in breaking this impeded aqueous flow. Curran’s observations and theories on PACG were finally accepted in 1951 following papers by Haas, Scheie, and Chandler, confirming the principle of “relative pupillary block.” Advances in gonioscopy prior to 1940, by Barkan, Trantas, Koeppe, Salzmann, and Troncoso, further helped define and distinguish the ACGs. The development of the Goldmann lens in 1938 allowed more universal use of gonioscopy, further advancing our knowledge and understanding of the anterior chamber angle.

In primary OAG, while the resistance to aqueous outflow is known to be increased, structures proximal to the trabecular meshwork do not add to the resistance to aqueous outflow and the pathologic resistance to outflow resides in the meshwork itself. Conversely, in ACG, the primary pathology is anatomical, proximal to the trabecular meshwork. Specifically, in such cases, the peripheral iris impedes the access of aqueous to the trabecular meshwork. The meshwork itself may be anatomically and functionally normal.

The ACGs are a diverse group of diseases. While the various forms of angle closure are unified by the presence of peripheral anterior synechiae (PAS) and/or iridotrabecular apposition, the mechanism of iris apposition or synechiae formation is varied. Moreover, the clinical presentation of angle closure varies from the abrupt and dramatic onset of acute ACG (20%–30% of cases) to the insidious and asymptomatic presentation of chronic ACG (70%–80% of cases).

In either presentation, acute or chronic, the physician must identify the anatomical changes within the angle and the underlying pathophysiology that has precipitated these changes in order to initiate the appropriate therapy. Early diagnosis and treatment of most forms of ACG can be invaluable, and sometimes curative. Accordingly, understanding the pathophysiology is essential if proper treatment is to be initiated. Also, screening patients at greatest risk for angle closure can be beneficial in