Histological landmarks in corneal dystrophy: pathology of corneal dystrophies.

Corneal dystrophies are bilateral, progressive, genetically determined noninflammatory diseases restricted to the cornea. These are characterized by deposition of nonnative protein or other material, both intracellular and extracellular, within the corneal layers. Dystrophies are classified based on the anatomical location of the lesions as: anterior corneal dystrophies (affecting the epithelium and extending into the superficial stroma), stromal dystrophies (which involve the stroma only) and posterior corneal dystrophies (which include the Descemet's membrane and endothelium). Recent additions in the field of genetics and molecular basis of the dystrophies have led to the evolution of a new classification which incorporates genotypic-phenotypic features. While histopathologic study is the gold standard for the diagnosis, various other techniques help provide additional information in this area. Corneal dystrophies can be considered unique as the association of gene-protein-disease has been approached both in the forward direction as well as the reverse order. In this chapter, we attempt to highlight the histological features of corneal dystrophies from the cumulative evidence obtained from the study of corneal buttons, enucleated specimens, corneal biopsies, electron microscopic studies, histochemistry and immunohistochemistry.