A comparative histologic study of the fibrillin microfibrillar system in the lens capsule of normal subjects and subjects with Marfan syndrome.

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Abstract

PURPOSE: To gain a better understanding of the pathogenesis of ectopia lentis and myopia in Marfan syndrome, studies were performed to determine the distribution and structure of fibrillin microfibrils in the lens capsule of normal subjects and of subjects with Marfan syndrome. METHODS: Frozen sections and/or flat mounts of lens capsules were prepared from six autopsy eyes, nine surgical capsulotomy specimens obtained at the time of cataract extraction, and five capsules from patients with Marfan syndrome obtained at intracapsular lens extraction. Avidin-biotin-peroxidase complex (ABC) immunoperoxidase or immunofluorescence staining with monoclonal antifibrillin antibody was used to localize fibrillin in lens capsules. Image analysis was also performed to compare the amount of fibrillin expression in normal and Marfan syndrome capsules. RESULTS: Based on fibrillin staining patterns, we identified three distinct zones in the equatorial and periequatorial regions of the normal lens capsule. Zone I, a 0.75-mm-wide peripheral ring of the anterior capsule, contained radial bundles of fibrillin fibers. In Zone II, a 1-mm-wide meshwork of fibrillin-rich fibers encircled the equator and served as an insertion platform for zonular fibers. Zone III was composed of radial, 0.1-mm-wide bands arranged in a periodic fashion in the most peripheral part of the posterior capsule. Fibrillin fibers were abnormal and disrupted in all three zones in patients with Marfan syndrome. The amount of fibrillin staining per unit area was significantly reduced in Marfan capsules compared with normal capsules (16-26% versus 49-56% per unit area, respectively; P < 0.001). CONCLUSIONS: Fibrillin was a major constituent of the peripheral and equatorial areas of the lens capsule. Zonular fibers, also rich in fibrillin, insert into the equatorial region, primarily in Zone II. Possibly, fibrillin played a role in the ability of the lens to change its configuration during accommodation. The observed qualitative and quantitative abnormalities in fibrillin expression in the lens capsule of patients with Marfan syndrome supported a causal relationship to lens abnormalities in these patients.