The Genetic Mysteries of the Corneal Dystrophies The Genetic ...

Features of Corneal Dystrophies andDegenerationsCorneal Degenerations (Examples)Feature Dystrophy DegenerationAge of Onset Early LateFamilial Yes NoSymmetry Symmetric AsymmetricInvolved Eye Bilateral UnilateralLocation Central PeripheralVascularity No YesInflammation No YesAssoc. disorders Rarely More frequent• Arcus senilis• Vogt’s limbal girdle• Marginal furrowdegeneration• Terrien’s degeneration• Pterygium• Salzmann’s nodulardegeneration• White ring of Coats• Band keratopathy• Corneal ectasias• Keratoconus• Non-hereditary• Pellucid MarginalDegenerationKeratoconus: Degeneration or Dystrophy?• Ectasia or thinning of the cornea-usually inferior/temporally• Hereditary in some cases• Autosomal dominant• Defective genes on chromosome 21 (SOD1 and VSX genes)• Etiology not known in non-hereditary cases-suspected causes:• eye rubbing• CL wear• Hormonal• Exacerbated by pregnancyClassification of the Corneal Dystrophies• Traditionally, classified by the affected corneal layer• Molecular genetics are changing this classification• Chromosome 1 Chromosome 4• Chromosome 5 Chromosome 9• Chromosome 12 Chromosome 16• Chromosome 17 Chromosome 20• Chromosome 21 X-chromosomeIC3D-2008 Classification of CornealDystrophies• Category 1: well-defined; gene mapped;mutations known• Category 2: well-defined; mapped to specificchromosomal loci but gene not yet identified• Category 3: well-defined; not mapped to anychromosomal locus• Category 4: suspected corneal dystrophyEpithelial Dystrophies• Epithelial Basement Membrane Dystrophy(EBMD) –Map/Dot/Fingerprint or Cogan’s• Meesman’s Dystrophy• Anterior Membrane Dystrophy• Band-shaped/Whorled Microcystic Dystrophy(Lisch dystrophy)• Recurrent Corneal Erosion Dystrophy2