the iridotrabecular apposition. This can occur directly with developmental anomalies such as anterior cleavage abnormalities, in which the iris insertion is more anterior into the scleral spur or meshwork; a thick peripheral iris, which on dilatation “rolls” into the trabecular meshwork; and/or anteriorly displaced ciliary processes, which may secondarily rotate the peripheral iris forward (plateau iris) into the meshwork. Another example of iris-induced angle closure is seen in aniridia, where the rudimentary iris leaflets rotate into the angle, resulting in secondary angle closure.
Primary Angle Closure
Primary angle closure is a complex disease entity that is a leading cause of glaucoma worldwide. Although the pathophysiology is complex and not completely understood, pupillary block is considered to be at least partially involved as the underlying cause in most cases of primary angle closure. Eyes with shorter axial lengths are at risk for PACG. Recent research suggests that regulation of iris volume may also play an important role in the pathogenesis of PACG. Whereas most eyes show a loss of iris volume with dilation of the pupil, eyes at risk for angle closure may have less ability to rid the iris stroma of water upon dilation. The retention of water within the stroma results in greater iris volume as the pupil dilates, crowding the angle and closing it in susceptible individuals. This dynamic feature of iris physiology may explain why only certain eyes with anatomically narrow angles develop overt angle closure.
Risk Factors for Developing Primary Angle Closure
Race
The prevalence of PACG in patients older than 40 years varies greatly depending on race: 0.1%–0.6% in whites, 0.1%–0.2% in blacks, 2.1%–5.0% in the Inuit, 0.4%–1.4% in East Asians, 0.3% in the Japanese, and 2.3% in a mixed ethnic group in South Africa. Some of these differences can be explained by the difference in the biometric parameters (anterior chamber depth, axial length) of the different white and Inuit populations, whereas the increased incidence in the Chinese and East Asian populations cannot be explained by biometric parameters alone. Most angle closure presents as an asymptomatic chronic disease without an acute attack. It has become increasingly clear that the burden of ACG is greater in Asian countries.
Bonomi L, Marchini G, Marraffa M, et al. Epidemiology of angle-closure glaucoma: prevalence, clinical types, and association with peripheral anterior chamber depth in the Egna-Neumarket Glaucoma Study. Ophthalmology. 2000;107(5):998–1003.
Dandona L, Dandona R, Mandal P, et al. Angle-closure glaucoma in an urban population in southern India: the Andhra Pradesh Eye Disease Study. Ophthalmology. 2000;107(9):1710–1716.
Foster PJ, Oen FT, Machin D, et al. The prevalence of glaucoma in Chinese residents of Singapore: a cross-sectional population survey of the Tanjong Pagar district. Arch Ophthalmol. 2000;118(8):1105–1111.
Quigley HA. Angle-closure glaucoma—simpler answers to complex mechanisms: LXVI Edward Jackson Memorial Lecture. Am J Ophthalmol. 2009;148(5):657–669.
Quigley HA. The iris is a sponge: a cause of angle closure. Ophthalmology. 2010;117(1):1–2.
Quigley HA, Broman AT. The number of people with glaucoma worldwide in 2010 and 2020. Br J Ophthalmol. 2006;90(3):262– 267.
Ocular biometrics
Patients who develop primary angle closure have small, “crowded” anterior segments and short axial lengths (ALs). The most important factors predisposing an eye to angle closure are a shallow anterior chamber, a thick lens, increased anterior curvature of the lens, a short AL, and a small corneal diameter and radius of curvature. An anterior chamber depth (ACD) of less than 2.5 mm predisposes
patients to primary angle closure, whereas most patients with primary angle closure have an ACD of less than 2.1 mm. With improvements in biometry techniques, a clear association between ACD and PAS has been demonstrated. While primary PAS seem to be uncommon with an ACD of greater than 2.4 mm, there is a strong correlation of increasing PAS formation with an ACD shallower than 2.4 mm. However, despite these generalizations, angle closure still occurs with deep anterior chambers in some cases.
The prevalence of ACG increases with each decade after 40 years of age. This increased prevalence has been explained by the increasing thickness and forward movement of the lens with age, and the resultant increase in iridolenticular contact. PACG is rare in persons younger than 40 years, and the etiology of angle closure in young individuals is most often related to structural or developmental anomalies rather than pupillary block.
Aung T, Nolan WP, Machin D, et al. Anterior chamber depth and the risk of primary angle closure in 2 East Asian populations. Arch Ophthalmol. 2005;123(4):527–532.
Devereux JG, Foster PJ, Baasanhu J, et al. Anterior chamber depth measurement as a screening tool for primary angle-closure glaucoma in an East Asian population. Arch Ophthalmol. 2000;118(2):257–263.
Ritch R, Chang BM, Liebmann JM. Angle closure in younger patients. Ophthalmology. 2003;110(10):1880–1889.
Gender
Primary angle closure has been reported 2 to 4 times more commonly in women than in men, irrespective of race. In studies assessing ocular biometry, women tend to have smaller anterior segments and ALs than do men. This difference does not appear to be large enough to explain this gender predilection.
Family history
The incidence of primary angle closure is increased in first-degree relatives of affected individuals. In whites, the prevalence of primary angle closure in first-degree relatives has been reported to be between 1% and 12%, whereas results from a survey in a Chinese population showed that the risk was 6 times greater in patients with any family history. In the Inuit, the relative risk in patients with a family history is increased 3.5 times compared with the general Inuit population. Such familial associations support a genetic influence in ACG; a gene associated with ACG was recently discovered.
Refraction
Primary angle closure occurs more commonly in patients with hyperopia, irrespective of race. Increasing rates of myopia, especially in Asia, have influenced the prevalence of this disease. Angle closure occurring in a patient with significant myopia should alert the clinician to search for secondary mechanisms such as microspherophakia, plateau iris configuration, or phacomorphic closure related to nuclear sclerotic cataract.
Acute Primary Angle Closure
Acute primary angle closure (PAC) occurs when IOP rises rapidly as a result of relatively sudden blockage of the trabecular meshwork by the iris. It is typically manifested by ocular pain, headache, blurred vision, and rainbow-colored halos around lights. Acute systemic distress may result in nausea and vomiting. The rise in IOP to relatively high levels causes corneal epithelial edema, which is responsible for the visual symptoms. Signs of acute angle closure include
high IOP
mid-dilated, sluggish, and irregularly shaped pupil corneal epithelial edema
congested episcleral and conjunctival blood vessels shallow anterior chamber
mild amount of aqueous flare and cells
Definitive diagnosis depends on the gonioscopic verification of angle closure. Gonioscopy should be possible in almost all cases of acute angle closure, although medical treatment of elevated IOP and clearing of corneal edema with topical glycerin may be necessary to enable visualization of the chamber angle. Dynamic gonioscopy may help the physician determine whether the iris– trabecular meshwork blockage is reversible (appositional closure) or irreversible (synechial closure), and it may also be therapeutic in breaking the attack of acute angle closure. Gonioscopy of the fellow eye in a patient with PAC usually reveals a narrow, occludable angle. The presence of a deep angle in the fellow eye should alert the clinician to search for alternative causes of elevated IOP. When performing gonioscopy, the clinician should observe the effect that the examination light has on the angle recess. For example, the pupillary constriction stimulated by the slit-lamp beam itself may open the angle and the narrow recess may go unrecognized (Fig 5-2).
Figure 5-2 Ultrasound biomicroscopy (UBM) of a narrow angle. A, Angle closure is evident when the angle is imaged with lights off. B, The same angle is much more open when imaged with lights on. (Courtesy of Yaniv Barkana, MD.)
During an acute attack, the IOP may be high enough to cause glaucomatous optic nerve damage, ischemic nerve damage, and/or retinal vascular occlusion. PAS can form rapidly, and IOP-induced ischemia may produce sector atrophy of the iris. Such atrophy releases pigment and causes pigmentary dusting of the iris surface and corneal endothelium. Iris ischemia, specifically of the iris sphincter muscle, may cause the pupil to become permanently fixed and dilated. Glaukomflecken, characteristic small anterior subcapsular lens opacities, may also develop as a result of ischemia. These findings are helpful in the detection of previous episodes of acute ACG.
The definitive treatment for acute angle closure is a laser iridotomy or, much less commonly, a surgical iridectomy; these procedures are discussed in detail in Chapter 8. Lensectomy is also a viable treatment option, although laser iridotomy may be more easily accomplished in the acute setting, especially if the eye is inflamed. Mild attacks may be broken by cholinergic agents (pilocarpine 1%– 2%), which induce miosis that pulls the peripheral iris away from the trabecular meshwork. Stronger miotics should be avoided, as they may increase the vascular congestion of the iris or rotate the lens– iris interface more anteriorly, increasing the pupillary block. Moreover, when the IOP is markedly elevated (eg, above 40–50 mm Hg), the pupillary sphincter may be ischemic and unresponsive to miotic agents alone. In this case, the patient should be treated with other agents, such as β-adrenergic antagonists; α2-adrenergic agonists; prostaglandin analogues; and oral, topical, or intravenous carbonic anhydrase inhibitors. When necessary, a hyperosmotic agent may be administered orally or intravenous carbonic anhydrase inhibitors. A hyperosmotic agent may be administered orally or intravenously or a paracentesis can be performed with a 30-gauge needle. The goal is to reduce the IOP to enable the miotic agent to constrict the pupil and break the block. Globe compression and dynamic gonioscopy have also been described to treat acute ACG. Nonselective adrenergic agonists or medications with significant α1-adrenergic activity (apraclonidine) should be avoided to prevent further pupillary dilation and iris ischemia.
In most cases of PACG, the fellow eye shares the anatomical predisposition for increased pupillary block and is at high risk of developing acute angle closure. This is especially true if the inciting mechanism included a systemic sympathomimetic agent such as a nasal decongestant or an anticholinergic agent. In addition, the pain and emotional upset resulting from the involvement of the first eye may increase sympathetic flow to the fellow eye and produce pupillary dilation. It is recommended that a peripheral iridotomy be performed in the other eye if a similar angle configuration is present. If the contralateral eye has a significantly different angle configuration, secondary ACGs must be strongly considered in the differential diagnosis. In general, PAC is a bilateral disease, and its occurrence in a patient whose fellow eye has a deep chamber angle raises the possibility of a secondary cause, such as a posterior segment mass, zonular insufficiency, or the iridocorneal endothelial (ICE) syndrome.
Laser iridotomy is the treatment of choice for PAC due to pupillary block. Surgical iridectomy or lensectomy with or without goniosynechialysis is indicated when laser iridotomy cannot be accomplished. Once an iridotomy or iridectomy has been performed, the pupillary block is relieved and the pressure gradient between the posterior and anterior chambers is normalized, which in most cases allows the iris to fall away from the trabecular meshwork. As a result, the anterior chamber deepens and the angle opens. If a laser iridotomy cannot be performed, the acute attack may be broken in 1 of 2 ways: the peripheral iris may be flattened with a laser iridoplasty or the pupillary block may be relieved with a laser pupilloplasty. In such cases, a peripheral iridectomy should be accomplished once the attack is broken and the cornea is of adequate clarity. Following resolution of the acute