Posterior Embryotoxon, Neurocristopathy

Definition

Posterior embryotoxon is a prominent, anteriorly displaced Schwalbe’s line that can extend 360° around the peripheral cornea or be isolated to a few clock hours, located most often, in the temporal aspect of the cornea. It can often be visualized on slit lamp exam, otherwise is seen gonioscopically.

Etiology

Dysgenesis of neural crest cells of the anterior chamber causes posterior embryotoxon. It can be isolated (i.e., considered normal) or be associated with a more extensive disease process such as Axenfeld-Rieger syndrome or Alagille’s syndrome. Less commonly, it is seen in congenital glaucoma or iridocorneal endothelial syndrome. Histologically, it appears as a central core of collagen and ground substance covered by a layer of spindle shaped cells and basement membrane. In Axenfeld-Rieger syndrome, iris strands may extend to the posterior embryotoxon.

Occurrence

Posterior embryotoxon is present in 8–15% of normal individuals. It is most commonly seen in Axenfeld-Rieger...