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Posterior polymorphous corneal dystrophy
Posterior polymorphous corneal dystrophy (PPCD) is a rare mild subtype of posterior corneal dystrophy (see this term) characterized by small aggregates of apparent vesicles bordered by a gray haze at the level of Descemet membrane, generally with no effect on vision.
Prevalence of this form of corneal dystrophy is unknown.
Lesions generally develop in early childhood and are mostly bilateral but may be asymmetrical or unilateral in some cases. Most patients are asymptomatic with no corneal edema, but progressive visual impairment due to stromal clouding may rarely occur.
PPCD is a genetically heterogenous condition with extremely variable expression. Three genes have been implicated: VSX1 (20p11.21), COL8A2 (1p34.2-p32.3), and ZEB1 (10p11.22), but the evidence implicating VSX1 and COL8A2 is questionable.
Multiple layers of collagen manifesting as focal fusiform or nodular excrescences are found on the posterior surface of Descemet membrane.
PPCD should be distinguished from congenital endothelial dystrophy type 1 (CHED1, see this term), since the two conditions share certain morphological and clinical features.
An autosomal dominant pattern of inheritance has been reported.
Management and treatment
Most patients with PPCD do not require therapy, but some may eventually require a penetrating keratoplasty or a procedure for repairing the posterior surface of the cornea, such as a deep lamellar endothelial keratoplasty (DLEK), Descemet stripping endothelial keratoplasty (DSEK), or Descemet stripping automated endothelial keratoplasty (DSAEK).