In the second wave, peripheral neural crest cells migrate between the newly formed corneal endothelium and surface ectoderm to form the keratocytes that will lead to formation of corneal stroma. The first wave involves the formation of the corneal endothelium as the neural crest cells migrate between the surface ectoderm and the lens. This typically occurs during the 7th week of gestation. Normal corneal development depends on neural crest migration which occurs in 3 distinctive waves during embryogenesis to produce the structures of the anterior chamber. The critical embryological event that is associated with Peters is the formation of the anterior chamber. The American Academy of Ophthalmology's Pathology Atlas contains a virtual microscopy image of Peters Anomaly. Peters type II also features lens abnormalities that can be seen histologically. The opacification often involves the central cornea however, it can also affect the entire cornea. Thinning, thickening, or absence of Bowman’s membrane and defects in the posterior stroma can occur, including residual fibrosis in the opacified stroma and central concave defect in the posterior corneal stroma (posterior ulcer) with disorderly stromal lamellae in the ulcer bed. Keratolenticular adhesions to the posterior cornea are also seen in some cases and can be visualized with slit lamp biomicroscopy or ultrasound biomicroscopy (UBM). Most commonly, the Descemet’s membrane of the cornea is absent, but there has also been a reported case of a “multiple-layer” structure of Descemet’s. There are diverse histological changes in Descemet’s membrane. Histologically, in Peters type I, the cornea at the area of opacity has an an endothelium with underlying iridocorneal synechiae that extend from the iris collarette to the border of the corneal opacity. Intrauterine infection and teratogenic exposures during pregnancy may also be associated with Peters. Fetal alcohol syndrome has been reported as a cause of Peters. In addition, a deficiency of heparan sulfate can lead to abnormal neural crest development in utero. Premature infants are at highest risk for development of ASD, including Peters anomaly. Peters Plus syndrome is an autosomal recessive congenital disorder affecting beta-1,3-galactosyltransferase-like glycosyltransferase gene(B3GALTL) on chromosome 13. In addition, lab studies on mice have shown that a deficiency of heparan sulfate leads to improper neural crest TGF-β2 signaling leading to ASD2. Peters can occur sporadically, but autosomal dominant and recessive inheritance have been reported. Reported chromosomal abnormalities in chromosomes 4, 13, 11, and 20 have been reported to contribute to Peters. The variety of genes involved contributes to the significant degree of phenotypic variability found in ASD. There have been multiple genetic loci that have been identified as causes for Peters anomaly including PAX6, PITX2, PITX3, FOXC1, FOXE3, CYP1B1, MAF and MYOC. Peters anomaly falls within the spectrum of anterior segment dysgenesis, which includes other diseases such as Axenfeld-Rieger syndrome. Peters is also associated with many other ocular pathologies including glaucoma, sclerocornea, corectopia, iris hypoplasia, cataract, ICE syndrome, aniridia, iris coloboma, persistent fetal vasculature and microcornea. ![]() Bilateral Peters is more strongly associated with systemic malformations (71.8%) as compared to unilateral Peters anomaly (36.8%). These systemic findings are seen in up to 60% of patients. Peters Plus syndrome includes short stature, developmental delay, dysmorphic facial features, cardiac, genitourinary, and central nervous system malformations. In both forms, opacification of the cornea leads to an amblyogenic effect on an infant's developing vision. 60% of those with Peters anomaly have bilateral involvement. Peters type II in addition features lens abnormalities and tend to be bilateral. Peters anomaly affects the iris, corneal endothelium, and Descemet’s membrane, leading to Peters type I. It has been known over the years as primary mesodermal dysgenesis of the cornea, congenital anterior synechiae, posterior keratoconus and anterior chamber cleavage syndrome. An estimate of 44-60 cases of Peters anomaly are reported in the United States annually. Peters anomaly is one disease in a constellation of diseases that causes corneal opacity due to anterior segment dysgenesis (ASD) during development. Coloboma and other anomalies of anterior segment ICD-9 743.44
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