Synchrotron X-ray diffraction in atypical macular dystrophy.

This report documents the first case of X-ray diffraction techniques aiding the diagnosis of a corneal dystrophy with a clinically ambiguous presentation. Post-operatively, a high-angle synchrotron X-ray diffraction pattern was obtained from an in vitro portion of a pathological cornea. This pattern displayed two X-ray reflections which we recently demonstrated to be unique to the high-angle X-ray diffraction patterns of both type I and type II macular dystrophy corneas; on the basis of this evidence we were able to offer a post-operative diagnosis of macular corneal dystrophy. An electron microscopical evaluation of the cornea revealed stromal lacunae at all levels and an extensive layer of vacuoles, predominantly between Bowman's layer and the anterior stroma. These vacuoles were often associated with large proteoglycan filaments, as identified by Cuprolinic blue staining. Abnormally large collagen fibrils were documented, for the first time, in a macular dystrophy cornea; they existed in localised regions, frequently adjacent to the vacuoles and abnormal proteoglycans, and could well have implications for corneal transparency. We propose that the dystrophy is an atypical variant of macular corneal dystrophy which is encompassed by the heterogeneous nature of the condition.