The IC3D classification of the corneal dystrophies [Ic3D-klassifikation von hornhautdystrophien]

Background: The recent availability of genetic analyses has demonstrated the shortcomings of the current phenotypic method of corneal dystrophy classification. Abnormalities in different genes can cause a single phenotype, whereas different defects in a single gene can cause different phenotypes. Some disorders termed corneal dystrophies do not appear to have a genetic basis. Purpose: The purpose of this study was to develop a new classification system for corneal dystrophies, integrating up-to-date information on phenotypic description, pathologic examination, and genetic analysis. Methods: The International Committee for Classification of Corneal Dystrophies (IC3D) was created to devise a current and accurate nomenclature. Results: This anatomic classification continues to organize dystrophies according to the level chiefly affected. Each dystrophy has a template summarizing genetic, clinical, and pathologic information. A category number from 1 through 4 is assigned, reflecting the level of evidence supporting the existence of a given dystrophy. The most defined dystrophies belong to category 1 (a welldefined corneal dystrophy in which a gene has been mapped and identified and specific mutations are known) and the least defined belong to category 4 (a suspected dystrophy where the clinical and genetic evidence is not yet convincing). The nomenclature may be updated over time as new information regarding the dystrophies becomes available. Conclusions: The IC3D Classification of Corneal Dystrophies is a new classification system that incorporates many aspects of the traditional definitions of corneal dystrophies with new genetic, clinical, and pathologic information. Standardized templates provide key information that includes a level of evidence for there being a corneal dystrophy. The system is user-friendly and upgradeable and can be retrieved on the website www.corneasociety.org/ic3d. Key Words: corneal dystrophy, inherited corneal disease, genetic corneal disease, corneal histopathology, gene, mutation, key reference, eponym, epithelial basement membrane dystrophy, epithelial recurrent erosion dystrophy, subepithelial mucinous corneal dystrophy, Meesmann corneal dystrophy, Lisch epithelial corneal dystrophy, gelatinous drop-like corneal dystrophy, Grayson-Wilbrandt corneal dystrophy, lattice corneal dystrophy, lattice gelsolin type dystrophy, granular corneal dystrophy 1, granular corneal dystrophy 2, Avellino corneal dystrophy, Reis-Bücklers corneal dystrophy, Thiel-Behnke corneal dystrophy, macular corneal dystrophy, Schnyder corneal dystrophy, Schnyder crystalline corneal dystrophy, congenital stromal corneal dystrophy, fleck corneal dystrophy, posterior amorphous corneal dystrophy, central cloudy dystrophy of Francxois, pre-Descemet corneal dystrophy, Fuchs endothelial corneal dystrophy, posterior polymorphous corneal dystrophy, congenital hereditary endothelial dystrophy 1, congenital hereditary endothelial dystrophy 2, X-linked endothelial corneal dystrophy.