Iridocorneal angle maturation begins during the 15th week of gestation through a combination of processes.85-87 Differential growth of the vascular tunic results in posterior movement of the iris and ciliary body relative to the trabecular meshwork and exposure of the outflow pathways.4 Schlemm's canal is identified during the 16th week.114 There is gradual cellular rearrangement and mesenchymal atrophy, as well as enlargement of numerous large spaces, until they become confluent with the anterior chamber.98 The corneal trabeculae enlarges and the corneal endothelium covering the angle recess regresses. The discontinuity of the cellular layer covering the angle and the many lacunae present in late gestation may be correlated with the normal development of an increase in the outflow facility of aqueous humor. It may be speculated that, if the splitting and rebuilding of the endothelial membrane lining of the early iridocorneal angle is arrested, a block to normal outflow may result. Persistence of the endothelial (Barkan's) membrane has been postulated to be of significance in the pathogenesis of congenital glaucoma.13,42,61,68,70,111 Postnatal remodeling of the drainage angle is associated with cellular necrosis and phagocytosis by macrophages, resulting in opening of the spaces of Fontana (clefts in the trabecular meshwork) and outflow pathways.86,87
Studies using staining for neuron-specific enolase (NSE) indicate that, although most of the structures of the iridocorneal angle are of neural crest origin, the endothelial lining of Schlemm's canal (like the vascular endothelium) is mesodermal.1,78
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