Anterior polar cataracts in CS rats: A predictor of mature cataract formation

PURPOSE. The objective of this study mas to characterize the morphology of the anterior opacities formed during recovery from posterior subcapsular ca taract (PSC) in Royal College of Surgeons (RCS) rats. METHODS. Lenses from. RCS rats at 8 and 12 weeks postnatal (n = 14 and 12, respectively) were examined under a dissecting microscope for the presence of anterior opacities. Lenses with anterior opacities were fixed, embedded in epoxy resin, and sectioned along the optic axis for light microscopy (LM ) and transmission electron microscopy (TEM). RESULTS. At eight weeks postnatal, 21.5% of animals (3/14) had anterior cat aracts. Light microscopy of 1- to 2-mu m thick sections revealed an anomalo us layer of material located at the epithelium-fiber interface, which was i dentified as a zone of liquefaction by TEM. Epithelial cells had minor stru ctural defects but were not necrotic. Anterior portions of elongating and c ortical fibers under the zone of liquefaction were undisrupted, whereas the ir posterior portions had numerous vacuoles.. The. anterior opacities were classified as anterior polar cataracts (APCs) based on the location and typ e of morphologic morphologic damage in the affected lenses. At twelve weeks postnatal, 25% of animals (3/12) bad APCs that involved prominent vesicula tion of the anterior cortex. Ultrastructural examination showed that large vesicles were located between and inside anterior fibers and that most extr acellular spaces were abnormally widened. Posteriorly, internalization of t he PSC by new fiber growth was disordered and displayed vesiculation and de nsity variations. In the bow region LM revealed minor structural irregulari ties that were identified as groups of apparently degenerating fibers by TE M. CONCLUSIONS. APCs in RCS rats are caused by degeneration of elongating fibe rs in the bow region and subsequent damage in the superficial anterior cort ex. The percentage of animals with APCs (25%) was consistent with the perce ntage of animals in which mature cataracts eventually develop. The morpholo gic changes, time of onset, and percentage of animals affected suggest that APC is the initial manifestation of mature cataract formation in RCS rats.