Samira Heydarian - Department of Rehabilitation Sciences, School of Allied Medical sciences, Mazandaran University of Medical Sciences, Sari, Iran

Corneal dystrophy is a common type of hereditary corneal diseases. It includes many types, which have varied pathology, histology and clinical manifestations. Corneal dystrophies are caused by the build-up of foreign material in one or more of the five layers of the cornea. Corneal dystrophies may not cause symptoms in some individuals; in others they may cause significant vision impairment. The age of onset and specific symptoms vary among the different forms of corneal dystrophy. The disorders have some similar characteristics; most forms of corneal dystrophy affect both eyes (bilateral), progress slowly, do not affect other areas of the body, and tend to run in families. There are more than 20 different types of corneal dystrophies. Traditionally, these disorders have been classified based upon their clinical findings and the specific layer of the cornea affected. Corneal dystrophies generally grouped into three categories: 1. Anterior or Superficial Corneal Dystrophies These dystrophies affect the outer two layers of cornea: the epithelium and the Bowman’s membrane. They include:  Epithelial basement membrane dystrophy  Lisch corneal dystrophy  Meesmann corneal dystrophy  Reis-Bucklers corneal dystrophy  Thiel-Behnke corneal dystrophy 2. Stromal Corneal Dystrophies These dystrophies usually affect the stroma, or center layer of cornea. They may also progress into other layers. Types in this group include:  Gelatinous drop-like corneal dystrophy  Granular corneal dystrophy  Lattice corneal dystrophy  Macular corneal dystrophy  Schnyder crystalline corneal dystrophy 3. Posterior Corneal Dystrophies This group affects the two innermost layers: The Descemet membrane and the endothelium. Included in this group are:  Congenital hereditary endothelial dystrophy  Fuchs’ endothelial corneal dystrophy  Posterior polymorphous corneal dystrophy Advances in molecular genetics have led to a greater understanding of these disorders. In this review we will discuss the clinical characteristics of different types of corneal dystrophies.