Stromal, descemet's and endothelial changes in macular corneal dystrophy type II

Purpose. A multi-faceted investigation of an individual macular corneal dystrophy (MCD) type II cornea from a 42-year-old female. Methods. Quantification of antigenic keratan sulphate in serum (ELISA with 5-D-4 antibody), synchrotron X-ray diffraction, energy dispersive X-ray microanalysis, and electron microscopic histochemistry (cuprolinic blue) and immunohistochemistry (5-D-4). Results. The level of antigenic keratan sulphate in our patient's serum was well below normal (19ng/ml compared to 251±78ng/ml). A characteristic 4.6Å X-ray reflection was evident, and the mid-stroma contained 30% less sulphur than normal. Close-packing of collagen was restricted to the superficial stroma. Abnormally-large proteoglycan filaments were noted throughout the extracellular matrix and Descemet's membrane's posterior non-banded zone, but not its anterior banded zone. Small, collagen-associated stromal proteoglycans were susceptible to digestion with chondroitinase ABC, but not keratanase I or N-glycanase. On occasion, collagen fibrils ranged in size from 20nm to 58nm, with preferential diameters of 34nm and 42nm. The endothelium expressed reduced anti-keratan sulphate labelling. Numerous endothelial inclusions were most likely due to intracellular fibrillogranular vacuoles similar to those found in the stroma. Conclusion. Based on our immunochemical findings it seems that a heterogeneity may exist within the MCD type II subgroup. Moreover, our patient's histopathology reveals pockets of large collagen fibrils, and proteoglycan abnormalities that involve Descemet's membrane and the endothelial cells.