X-RAY-DIFFRACTION AND TRANSMISSION ELECTRON-MICROSCOPY OF MORQUIO-SYNDROME TYPE-A CORNEA - A STRUCTURAL-ANALYSIS

Purpose. This case report describes the structural characterization of the corneal stroma from a patient with Morquio syndrome type A. Metho ds, A left penetrating keratoplasty was performed, and the cornea was examined using transmission electron microscopy and synchrotron x-ray diffraction. The interfibrillar proteoglycans were visualized in the e lectron microscope by using cuprolinic blue. Results, Stromal collagen fibrils showed a bimodal distribution of diameters: 70% had a distrib ution comparable to that in normal tissue (20-30 nm), and 30% containe d larger fibrils (30-42 nm) as seen by electron microscopy. Both elect ron microscopy and x-ray diffraction showed that the bulk numeric dens ity of fibrils per unit area in cross-section (number density) was hig her than normal in the Morquio syndrome cornea. The arrangement of pro teoglycans throughout most of the Morquio syndrome cornea appeared nor mal, but many of the filaments were twice their normal length. In the anterior stroma, very large proteoglycan filaments (less than or equal to 400 nm long) were found. Other ultrastructural differences also we re noted, including abnormal keratocytes and long spacing collagen. Co nclusion, The variation in fibril diameter and number density were mod eled to account for only a 5% decrease in light scattering compared wi th the normal cornea. The extensive corneal clouding seen in the Morqu io syndrome cornea cannot therefore be attributed to the variation in fibril diameters; collagen-free areas and expanded cells seem to be th e most likely cause.