THE STRUCTURE OF POSTERIOR SUBCAPSULAR CATARACTS IN THE ROYAL-COLLEGEOF SURGEONS (RCS) RATS

The Royal College of Surgeons (RCS) rat is an animal model for human a utosomal recessive retinitis pigmentosa. As the retinas of these anima ls degenerate from two to six weeks after birth, posterior subcapsular cataracts (PSCs) develop, presumably in response to toxic lipid perox ides formed by degenerating rod outer segments. Morphologically, these PSCs are thought to be characterized by a proliferation of dysplastic bladder-like fibers, or Wedl cells, in the meridional region of the l ens, that subsequently migrate to, and aggregate at, the posterior pol e as the PSC. This report presents the results of correlative scanning (SEM) and transmission (TEM) electron microscopic as well as light mi croscopic (LM) analysis of the ultrastructure of RCS PSCs, SEM analysi s of two, four and six week old lenses (n = 6-10 specimens per age gro up) demonstrated that the PSCs of RCS rats resulted from a growth malf ormation of the posterior fiber ends from four to six weeks. The PSC i s composed of markedly enlarged and irregular posterior fiber ends abe rrantly curved away from the polar axis toward the vitreous rather tha n overlapping and abutting to form suture branches within and between concentric growth shells. LM analysis revealed evidence of progressive ly more numerous, enlarged, and irregular, ovate cellular profiles at the posterior pole from four to six weeks. However, there was no evide nce of Wedl cells either within the meridional row region or along a m igratory path from the equator to the posterior pole at any age. TEM a nalysis confirmed that the size and abnormal shapes of cellular profil es were consistent with SEM analysis and that nuclei were never observ ed within the plaque. In addition, there was considerable variation in cytoplasmic densities between cells, Also, dense deposits were freque ntly noted between cells and beneath the capsule. The orientation of p osterior fiber end profiles to the posterior capsule was 45, 70 and 90 degrees at respectively two, four and six weeks of age. These results show that RCS PSCs are a consequence of abnormal posterior fiber end growth culminating in a posterior opacity. (C) 1998 Academic Press.