In contrast to nuclear cataracts, cortical cataracts are associated with local disruption of the structure of mature lens fiber cells. Once membrane integrity is compromised, essential metabolites are lost from the affected cells. This loss leads to extensive protein oxidation and precipitation. Like nuclear cataracts, cortical cataracts are usually bilateral but are often asymmetric. Their effect on visual function varies greatly, depending on the location of the opacity relative to the visual axis. A common symptom of cortical cataracts is glare from intense focal light sources, such as car headlights. Monocular diplopia may also result. Cortical cataracts vary greatly in their rate of progression; some cortical opacities remain unchanged for prolonged periods, while others progress rapidly.
On examination with the slit-lamp biomicroscope, the first visible signs of cortical cataract formation are vacuoles (Fig 5-3) and water clefts in the anterior or posterior cortex. The cortical lamellae may be separated by fluid. Wedge-shaped opacities (often called cortical spokes or cuneiform opacities) form near the periphery of the lens, with the pointed end of the opacities oriented toward the center (Fig 5-4). The cortical spokes appear as white opacities when viewed with the slit-lamp biomicroscope and as dark shadows when viewed by retroillumination. The wedge-shaped opacities may spread to adjacent fiber cells and along the length of affected fibers, causing the degree of opacity to increase and extend toward the visual axis. When the entire cortex, from the capsule to the nucleus, becomes white and opaque, the cataract is said to be mature (Fig 5-5). In mature opacities, the lens absorbs water, becoming swollen and enlarged (termed intumescent cortical cataract); such cataracts may lead to angle-closure glaucoma.
When degenerated cortical material leaks through the lens capsule, leaving the capsule wrinkled and shrunken, the cataract is referred to as hypermature (Fig 5-6). When further liquefaction of the cortex allows free movement of the nucleus within the capsular bag, the cataract is described as morgagnian (Fig 5-7).
On histologic examination, cortical cataracts are characterized by local swelling and disruption of the lens fiber cells. Globules of eosinophilic material (morgagnian globules) are observed in slitlike spaces between lens fibers (see Fig 9-11 in BCSC Section 4, Ophthalmic Pathology and Intraocular Tumors).
Figure 5-3 Early cortical cataract development as viewed at the slit lamp using retroillumination. A, Vacuoles in the periphery of a combined cataract with central PSC plaque. B, Typical cortical spokes.
(Courtesy of James Gilman, CRA, FOPS.)
Figure 5-4 Cortical cataract. A, Cortical cataract viewed by oblique view at the slit lamp. B, Schematic of immature cortical cataract.
(Part A courtesy of James Gilman, CRA, FOPS; part B illustration by Mark Miller.)
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.