Classification of the primary corneal dystrophies has until now been based on biomicroscopic and pathologic features. Depending on the location of dystrophic deposits, the main anatomic groupings have been epithelial and subepithelial dystrophies, dystrophies primarily affecting the Bowman layer, stromal dystrophies, and endothelial dystrophies.
Recent advances in our understanding of the molecular genetics and pathophysiology of certain corneal dystrophies proffer a paradigm shift regarding the classification of these disorders. The greatest strides have occurred in the study of stromal corneal dystrophies. In 1994, Stone et al1 mapped the genetic defect in 2 families with granular dystrophy, 2 families with lattice dystrophy, and 4 families with Avellino dystrophy to chromosome 5q. Subsequently, Munier et al2 refined the location to chromosome 5q.31 for families with granular, lattice, Avellino, and Reis-Bucklers dystrophy, and isolated the candidate gene BIGH3 (the transforming growth factor β–induced gene). Since then, mutations in this gene have been shown to be responsible for a number of phenotypically distinct entities: granular corneal dystrophy type I, type II (formerly Avellino corneal dystrophy), and type III (formerly Reis-Bucklers dystrophy); lattice corneal dystrophy type I, type IIIA, type IIIA-like, and type IV; and Thiel-Behnke dystrophy. The molecular genetics of these and other corneal dystrophies has been well summarized recently by Klintworth.3
Dunaief JL, Ng EWM, Goldberg MF. Corneal Dystrophies of Epithelial GenesisThe Possible Therapeutic Use of Limbal Stem Cell Transplantation. Arch Ophthalmol. 2001;119(1):120-122. doi:10-1001/pubs.Ophthalmol.-ISSN-0003-9950-119-1-eed00006