Cataract and Other Lens Abnormalities
Mild thickening of the lens capsule can be associated with pathologic proliferation of lens epithelium or with chronic inflammation of the anterior segment. Elements with an affinity for basement membranes, such as copper or silver, can form pigmented deposits in the anterior lens capsule, conditions known as chalcosis and argyrosis, respectively.
The most common abnormality involving the lens epithelium may be posterior subcapsular cataract (Fig 9-7A; see also Fig 9-8A). Histologically, development of this cataract begins with epithelial disarray at the lens equator, followed by posterior migration of the lens epithelial cells along the posterior capsule. As the cells migrate posteriorly, they may enlarge significantly because of retention of lens protein in the cytoplasm. These swollen cells, referred to as Wedl (or bladder) cells, can cause significant visual impairment if they involve the axial portion of the lens (Fig 9-7B).
Inflammation, ischemia, or trauma can result in injury to the lens epithelium, stimulating epithelial metaplasia and the formation of anterior subcapsular fibrous plaques (Fig 9-8A). In this condition, the epithelial cells have undergone a metaplastic transformation into fibroblast-like cells that form a plaque just interior to the anterior capsule. Following resolution of the inciting stimulus, the lens epithelium may produce another capsule, thereby completely surrounding the fibrous plaque and creating what is called a duplication cataract (Fig 9-8B).
Figure 9-7 Posterior subcapsular cataract. A, Cataract (arrow) viewed at the slit lamp. B, Oval to round nucleated Wedl cells (arrows) and smaller lens epithelial cells line the posterior lens capsule (arrowhead).
(Part A courtesy of Arlene V. Drack, MD; part B courtesy of Robert H. Rosa Jr, MD.)
Figure 9-8 Anterior and posterior subcapsular cataracts. A, Gross photograph shows white anterior (arrow) and posterior (arrowhead) subcapsular plaques located centrally. B, A fibrous plaque (asterisk) is present internal to the original lens capsule (arrowhead).
(Part A courtesy of Tatyana Milman, MD; part B courtesy of Hans E. Grossniklaus, MD.)
Disruption of the lens capsule often results in proliferation of lens epithelial cells. For example, following extracapsular cataract extraction, remaining epithelial cells can proliferate and cover the inner surface of the posterior lens capsule, resulting in clinically appreciable posterior capsule opacification. These accumulations of proliferating epithelial cells may form partially transparent globular masses, referred to as Elschnig pearls (Fig 9-9), which are histologically identical to Wedl cells. Sequestration of proliferating lens fibers in the equatorial region may create a doughnut-shaped remnant, known as a Soemmering ring secondary cataract (Fig 9-10).
Severe elevation of intraocular pressure can damage lens epithelial cells, leading to cell degeneration. Clinically, patches of white flecks (glaukomflecken) are observed beneath the anterior lens capsule. Histologic examination shows focal areas of necrotic lens epithelial cells, often with associated degenerated cortical material. See also BCSC Section 10, Glaucoma.
Figure 9-9 Elschnig pearls. A, Clinical appearance with slit-lamp retroillumination, demonstrating numerous cystic posterior capsule opacities behind the lens implant. B, Photomicrograph depicts proliferating lens epithelium (arrows) on remnants of the posterior capsule (PAS stain).
(Part A courtesy of Sander Dubovy, MD; part B courtesy of Nasreen A. Syed, MD.)
Figure 9-10 Soemmering ring secondary cataract. A, Doughnut-shaped white cataractous material is present in the equatorial region of the lens capsule and surrounds a lens haptic (arrows). The lens optic and a second haptic are positioned in front of the lens capsular bag, in the sulcus. B, Photomicrograph shows accumulation of lens protein in the residual equatorial lens capsule (arrows).
(Part A courtesy of Tatyana Milman, MD.)
Retention of iron-containing metallic foreign bodies in the eye or long-standing intraocular hemorrhage may result in iron deposition in the lens epithelial cells from siderosis or hemosiderosis. The iron is toxic to the epithelial cells. The presence of iron within the epithelial cells can be demonstrated with Perls Prussian blue stain.
Clinically, cortical degenerative changes fall into 2 broad categories: (1) generalized discolorations with loss of transparency; and (2) focal opacifications. Generalized loss of transparency cannot be reliably diagnosed histologically; the histologic stains used to colorize the lens tissue after it is processed prevent the assessment of lens clarity. The earliest sign of focal cortical degeneration is hydropic swelling of the lens fibers with decreased intensity of eosinophilic staining. Focal cortical opacities become more apparent when fiber degeneration is advanced enough to cause liquefactive change. Light microscopy shows the accumulation of eosinophilic globules (morgagnian globules) in slitlike spaces between the lens fibers (Fig 9-11; see also Fig 9-12C). As focal cortical lesions progress, these spaces become confluent and form globular collections of lens protein. Ultimately, the entire cortex can become liquefied, allowing the nucleus to sink inferiorly and the capsule to wrinkle; this condition is referred to as morgagnian cataract (Fig 9-12).
In the adult lens, the continual production of lens fibers subjects the nucleus to the stress of mechanical compression, which causes hardening of the lens nucleus. Aging is also associated with alterations in the chemical composition of the nuclear fibers that contribute to changes in color and refractive index. The pathogenesis of nuclear discoloration is poorly understood and probably involves more than one mechanism, including accumulation of urochrome pigment. Clinically, the lens nucleus may appear yellow, brunescent, or dark brown.
Figure 9-11 Cataract. A, Extensive cortical changes are present (asterisk).B, Cortical degeneration. Lens cell fibers (asterisk) are swollen and fragmented. Note the morgagnian globules (arrowheads). The lenticular fragments, which are opaque, increase osmotic pressure within the capsule.
(Courtesy of Hans E. Grossniklaus, MD.)
Figure 9-12 Morgagnian cataract. A, The brunescent nucleus has sunk inferiorly within the liquefied cortex. Arrows mark the superior edge of the nucleus. B, The lens cortex has liquefied, leaving the lens nucleus (asterisk) floating freely within the capsular bag. C, Artifactitious, sharply angulated clefts (arrows) are present in this nuclear sclerotic cataract. A zone of morgagnian globules (M) is visible.
(Part A courtesy of Bradford Tannen, MD; part B courtesy of Debra J. Shetlar, MD.)
Figure 9-13 Crystalline deposits of calcium oxalate (arrows) are visible within the lens. Also apparent is a cortical cleft with morgagnian globules (arrowheads).
(Courtesy of Tatyana Milman, MD.)
Nuclear cataracts are difficult to assess histologically because they take on a subtle homogeneous eosinophilic appearance. Clinically, the loss of laminations (artifactitious clefts) probably correlates better with nuclear firmness than it does with optical opacification (see Fig 9-12C). Occasionally, crystalline deposits, identified as calcium oxalate, may be observed within a nuclear cataract (Fig 9-13). These deposits are birefringent under polarized light. It is postulated that oxidative DNA damage to lens epithelial cells may contribute to age-related nuclear cataract.
Deposition of abnormal protein on the lens zonular fibers in pseudoexfoliation syndrome (also called exfoliation syndrome) can lead to degeneration of these fibers and their eventual dehiscence. See Chapter 7 in this volume for additional discussion of pseudoexfoliation syndrome. See also Chapter 5 in BCSC Section 11, Lens and Cataract.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.