Anterior Segment Dysgenesis
The term anterior segment dysgenesis refers to a spectrum of developmental anomalies resulting from abnormalities of neural crest cell migration and differentiation during embryologic development (eg, Axenfeld-Rieger syndrome, Peters anomaly, posterior keratoconus, and iridoschisis). Maldevelopment of the anterior chamber angle is most prominent in Axenfeld-Rieger syndrome, an autosomal dominant disorder, which itself encompasses a spectrum of anomalies, ranging from isolated bilateral ocular defects to a fully manifested systemic disorder.
Ocular manifestations of Axenfeld-Rieger syndrome include posterior embryotoxon, iris strands attached to the Schwalbe line, iris hypoplasia and atrophy, corectopia and pseudopolycoria, a maldeveloped or “fetal” anterior chamber angle (discussed earlier), and glaucoma in 50% of the cases occurring in late childhood or adulthood (Figs 7-4, 7-5). Posterior embryotoxon is often described as a thickening of Descemet membrane at its termination (Schwalbe line), but it is, in fact, a nodular thickening of the collagen just under the terminal portion of Descemet membrane. See also BCSC Section 8, External Disease and Cornea.
Figure 7-4 Posterior embryotoxon. Light micrograph shows a nodular, collagenous prominence under the termination of Descemet membrane (arrow). TM = trabecular meshwork.
(Courtesy of Hans E. Grossniklaus, MD.)
Chang TC, Summers CG, Schimmenti LA, Grajewski AL. Axenfeld-Rieger syndrome: new perspectives. Br J Ophthalmol. 2012;96(3):318–322.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.