Posterior Capsule Opacification
The most common late occurrence after cataract surgery by means of ECCE or phacoemulsification is posterior capsule opacification (PCO). In addition, contracture of a continuous curvilinear capsulorrhexis may occlude the visual axis because of anterior capsule fibrosis and phimosis.
Capsular opacification stems from the continued viability of lens epithelial cells that remain after removal of the nucleus and cortex. Opaque secondary membranes are formed by proliferating lens epithelial cells, fibroblastic metaplasia, and collagen deposition. Lens epithelial cells proliferate in several patterns. Sequestration of nucleated bladder cells (Wedl cells) in a closed space between the adherent edges of the anterior and posterior capsule results in a doughnut-shaped configuration, referred to as a Soemmering ring. If the epithelial cells migrate out of the capsular bag, translucent globular masses resembling fish eggs (Elschnig pearls) form on the edge of the capsular opening. These pearls can fill the pupil or remain hidden behind the iris. Histologic examination shows that these “fish eggs” are nucleated bladder cells, identical to those proliferating within the capsule of a Soemmering ring but usually lacking a basement membrane. If the epithelial cells migrate across the anterior or posterior capsule, they may cause capsular wrinkling and opacification. These lens epithelial cells are capable of undergoing metaplasia with conversion to myofibroblasts. These cells can produce a matrix of fibrous and basement membrane collagen. Contraction of this collagen matrix causes wrinkles in the posterior capsule, with resultant distortion of vision and glare.
The reported incidence of PCO varies widely but has been diminishing as a result of modern IOL designs and placement. Older studies reported that the frequency of Nd:YAG laser capsulotomy varied between 3% and 53% within 3 years of cataract surgery. More recent clinical series with a 3- to 5-year follow-up of cases with either hydrophobic acrylic or silicone square-edge design show PCO rates up to 5%. IOL design is now considered the dominant factor both in inhibiting posterior migration of lens epithelial cells and in influencing the rate of PCO. The IOL material also has a modest effect on opacification rates. Hydrogel IOLs are associated with the highest rate, followed by PMMA, then silicone; IOLs made of hydrophobic acrylic material are associated with the lowest rate. Compared to round-edge optics, the truncated square-edge optic design is associated with lower rates of PCO in both silicone and acrylic IOLs, although these lenses may increase the incidence of undesirable optical reflections and positive dysphotopsias. See BCSC Section 3, Clinical Optics, for further discussion of IOL design.
Other factors thought to increase PCO rate include:
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younger age of the patient
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history of intraocular inflammation
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pseudoexfoliation syndrome
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anterior capsulorrhexis that does not cover 360° of the IOL edge
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incomplete cortical cleanup
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round-edge design of the IOL optic
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time elapsed since surgery
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presence of silicone oil
There seems to be no difference in PCO rates with prolonged use of postoperative topical corticosteroids or NSAIDs.
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Rönbeck M, Zetterström C, Wejde G, Kugelberg M. Comparison of posterior capsule opacification development with 3 intraocular lens types: five-year prospective study. J Cataract Refract Surg. 2009;35(11):1935–1940.
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.