Lens-Induced Angle Closure
The mechanism of phacomorphic glaucoma is typically multifactorial. However, by definition, a significant component of the pathologic angle narrowing is related to the acquired mass effect of the cataractous lens itself. As seen in the primary angle-closure (PAC) spectrum, pupillary block often plays an important role in this condition. Phacomorphic narrowing of the angle generally occurs slowly with formation of the cataract. However, in some cases, the onset may be acute and rapid, precipitated by marked lens swelling (intumescence) as a result of cataract formation and the development of pupillary block in an eye that is not otherwise anatomically predisposed to closure (Figs 10-1, 10-2).
Table 10-1 Underlying Mechanisms of Non–Pupillary Block Angle Closure
Distinguishing between the PAC spectrum and phacomorphic angle closure is not always straightforward, but making the distinction may not be necessary, as the treatment of both conditions is similar. However, the anterior chamber depth (ACD), gonioscopic appearance, and degree of cataract differ between eyes on the PAC spectrum and those with phacomorphic angle closure, and these differences can help the clinician determine the etiology (see also BCSC Section 11, Lens and Cataract). Several methods of anterior segment imaging (anterior segment optical coherence tomography [AS-OCT], ultrasound biomicroscopy [UBM], and Scheimpflug) provide parameters that can assist in the diagnosis. For example, AS-OCT in patients with phacomorphic angle closure showed that the ACD was about half that of control eyes (1.4 mm vs 2.8 mm) and that the lens vault was triple the value of controls (1.4 mm vs 0.4 mm).
Figure 10-1 Phacomorphic glaucoma. Lens intumescence precipitates pupillary block and secondary angle closure in an eye not anatomically predisposed to angle closure.
Figure 10-2 Phacomorphic glaucoma. A, In this example, the angle remains narrow despite a patent iridotomy. B, In bright light, the angle is transiently made deeper by pupil constriction. C, In this case, a longer-term solution is provided by thinning the peripheral iris with laser iridoplasty. Lensectomy is also an effective treatment strategy.
(Courtesy of Yaniv Barkana, MD.)
Laser peripheral iridotomy (LPI) followed by cataract extraction in a quiet eye is the traditional treatment. However, in many cases, the iridotomy is unnecessary, because cataract surgery is the definitive treatment in eyes that have the potential for improved vision. Cholinergic agents have no role in the treatment of this condition because they may further narrow the angle (by increasing the pupillary block and causing forward movement of the lens–iris interface due to zonular laxity) and worsen vision in the presence of cataract. In addition, the miotic pupil makes subsequent cataract surgery more challenging.
Ectopia lentis is defined as displacement of the crystalline lens from its normal anatomic position (Fig 3-10). With forward displacement, pupillary block may occur, resulting in iris bombé, shallowing of the anterior chamber angle, and secondary angle closure. Common causes of lens subluxation include
sulfite oxidase deficiency
The most common cause of acquired zonular insufficiency and crystalline lens subluxation is pseudoexfoliation syndrome (Fig 4-10).
Figure 10-3 Ectopia lentis: dislocation of the lens into the anterior chamber through a dilated pupil.
(Courtesy of Ron Gross, MD.)
Figure 10-4 Pseudoexfoliation syndrome is a common cause of subluxation of the crystalline lens. A, Right eye of a patient with complete dislocation of the lens. B, Gonioscopic view of the same eye reveals that the dislocated lens is in the inferior vitreous cavity. C, Left eye (same patient) showing subluxation of the lens.
(Courtesy of Thomas W. Samuelson, MD.)
The treatment of choice is the creation of 2 laser iridotomies 180° apart so that both will not be occluded simultaneously by the lens. This relieves the pupillary block and is a temporizing measure until more definitive lensectomy, if indicated to improve visual function, can be performed. Lens extraction is usually indicated to restore vision and to reduce the risk of recurrent pupillary block and peripheral anterior synechiae (PAS) formation.
Microspherophakia, a congenital disorder in which the lens has a spherical or globular shape, may cause ectopia lentis and subsequent pupillary block with resultant angle closure (Fig 5-10). Treatment with cycloplegia may tighten the zonules, flatten the lens, and pull it posteriorly, breaking the pupillary block. Miotics may make the condition worse by increasing the pupillary block and by rotating the ciliary body forward, loosening the zonules and allowing the lens to become more globular. Microspherophakia is often familial and may occur as an isolated condition or as part of Weill-Marchesani or Marfan syndrome.
Aphakic or pseudophakic angle closure
Pupillary block may occur in aphakic and pseudophakic eyes. Vitreous can block the pupil and/or an iridotomy site in aphakic or pseudophakic eyes or in a phakic eye with a dislocated lens. Generally, the anterior chamber shallows, and the iris assumes a bombé configuration. Treatment with mydriatic and cycloplegic agents may restore aqueous flow through the pupil but may also make performing a laser iridotomy difficult initially. Topical β-adrenergic antagonists, α2-adrenergic agonists, carbonic anhydrase inhibitors, and hyperosmotic agents can be effective in reducing intraocular pressure (IOP) prior to performing an iridotomy. One or more laser iridotomies may be required.
Pupillary block may also occur with anterior chamber intraocular lenses (ACIOLs). An iridectomy or early postoperative iridotomy should be performed when an ACIOL is implanted. This is to prevent pupillary block from developing as a result of apposition of the iris to the ACIOL optic or apposition of the vitreous face to the pupil–optic complex. If pupillary block occurs, the peripheral iris bows forward around the ACIOL and occludes the angle. In this instance, the central chamber remains deep relative to the peripheral chamber because the ACIOL itself prevents the central portions of the iris and vitreous face from moving forward. Laser iridotomies, often multiple, are required to relieve the pupillary block. In rare cases, pupillary block can occur in the presence of an iridectomy if the lens haptic or vitreous obstructs the iridectomy site or the pupil.
Figure 10-5 Ectopia lentis due to microspherophakia. The lens (arrow) is trapped anteriorly by the pupil, resulting in iris bombé and a dramatic shallowing of the anterior chamber.
(Courtesy of G.L. Spaeth, MD.)
In addition, pupillary block can occur following posterior capsulotomy when vitreous obstructs the pupil. A condition referred to as capsular block may also be seen, wherein retained viscoelastic or fluid in the capsular bag pushes a posterior chamber intraocular lens (IOL) anteriorly, which may narrow the angle.
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.