A COMPARATIVE HISTOLOGIC-STUDY OF THE FIBRILLIN MICROFIBRILLAR SYSTEMIN THE LENS CAPSULE OF NORMAL SUBJECTS AND SUBJECTS WITH MARFAN-SYNDROME

PURPOSE To gain a better understanding of the pathogenesis of ectopia lentis and myopia in Marfan syndrome, studies were performed to determ ine the distribution and structure of fibrillin microfibrils in the le ns capsule of normal subjects and of subjects with Marfan syndrome. ME THODS. Frozen sections and/or flat mounts of lens capsules were prepar ed from six autopsy eyes, nine surgical capsulotomy specimens obtained at the time of cataract extraction, and five capsules from patients w ith 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 compa re the amount of fibrillin expression in normal and Marfan syndrome ca psules. RESULTS. Based on fibrillin staining patterns, we identified t hree distinct zones in the equatorial and periequatorial regions of th e normal lens capsule. Zone I, a 0.75-mm-wide peripheral ring of the a nterior capsule, contained radial bundles of fibrillin fibers. In Zone II, a 1-mm-wide meshwork of fibrillin-rich fibers encircled the equat or and served as an insertion platform for zonular fibers. Zone III wa s composed of radial, 0.1-mm-wide bands arranged in a periodic fashion in the most peripheral part of the posterior capsule. Fibrillin fiber s were abnormal and disrupted in all three zones in patients with Marf an syndrome. The amount of fibrillin staining per unit area was signif icantly reduced in Marfan capsules compared with normal capsules (16-2 6%; versus 49-56% per unit area, respectively; P < 0.001). CONCLUSIONS . Fibrillin was a major constituent of the peripheral and equatorial a reas of the lens capsule. Zonular fibers, also rich in fibrillin, inse rt into the equatorial region, primarily in Zone II. Possibly, fibrill in played a role in the ability of the lens to change its configuratio n during accommodation. The observed qualitative and quantitative abno rmalities in fibrillin expression in the lens capsule of patients with Marfan syndrome supported a causal relationship to lens abnormalities in these patients.