What is Peters' anomaly of the cornea?

Peters' Anomaly of the Cornea
Definition: Peters' anomaly can be defined as a congenital corneal central opacity associated with a posterior defect in Descemet's membrane and endothelium. Two types have been defined.
Type 1 is unilateral, characterized by a central or paracentral corneal opacity with iris strands that arise from the iris collarette and attach to the cornea.
Type 2 is bilateral in 60% of the cases and shows lens adherence to the posterior cornea due to lack of separation from the lens. This finding is associated with cataract.
Incidence/Prevalence: rare
Etiology: Most cases are sporadic, yet both autosomal recessive and dominant modes of inheritance are reported. Peter’s anomaly is considered an alteration of the migration of waves of neural crest. Reported chromosomal anomalies include ring chromosome 20, trisomy 13, and partial deletion of the long arm of chromosome 11. Mutations occur at the PAX 6 locus on chromosome 11p13 in some Peters' anomaly patients. The anomaly has been reported as a feature of fetal alcohol syndrome.
Clinical Findings: Initially, a defect in corneal endothelium and Descemet's membrane is present, often with marked corneal edema. The edema may extend well beyond the defect giving rise to the central leukoma. A doughnut pattern of the congenital leukoma is highly suggestive of Peter's anomaly (white arrows numbers 1). Over time the surrounding endothelium covers the defect and produces new basement membrane. The edema regresses only to leave the corneal opacity. 50% of cases of Peter’s anomaly may be associated with a variety of ocular abnormalities including: bilateral glaucoma, sclerocornea, corectopia, iris hypoplasia, anterior polar cataract, iris corneal adhesion, keratolenticular touch, microcornea, aniridia, chorioretinal coloboma, iris coloboma, persistence and hyperplasia of the primary vitreous, microphthalmos, and optic nerve hypoplasia.
Systemic abnormalities associated with Peter’s anomaly include craniofacial dysostosis, hydrocephalus, pulmonary hypoplasia, cleft lip and palate, cardiac, and GU malformations.
Histopathology: The key findings are iris stromal fibers that join the collarette (arrow #2) and central cornea, in combination with an absent Descemet’s membrane and endothelium in the central cornea (arrow number 1 and black arrow 3, and number 4) as well as at sites of irido-keratic adhesion. The cornea may appear to have a divot taken from the posterior surface (posterior keratoconus, number 4) . Bowman’s layer may appear to be thicker than normal (black arrow number 5 and lighted arrow below in higher magnification, PAS stained section). Note the clear, branching, subtle channel at the lighted arrow, which is where a corneal nerve is fortuitously captured crossing the thickened Bowman's layer!
Treatment: Penetrating keratoplasty is often performed to correct the leukoma in bilateral cases. However, some authors contend that cases in which the fellow eye is normal do not warrant surgery.