Anterior segment anomalies of the eye constitute a complex spectrum of overlapping phenotypic disorders resulting from malformations of endothelial tissues during the differentiation of the neural crest, and are collectively grouped as Axenfeld–Rieger syndrome (Shields et al. 1985; Alward 2000). Patients are considered to have Axenfeld−Rieger anomaly (ARA) when iris strands bridge the iridocorneal angle to the trabecular meshwork and the posterior embryotoxon. Axenfeld−Rieger anomaly is an autosomal-dominant disorder not associated with clinical symptoms, consisting of a number of developmental anomalies in the region where the iris approaches the cornea. In many eyes the iris root appears hypoplastic and becomes stretched, resulting in arcardic stromal fenestration. A thin, impermeable membrane extends with delaying fibrillae from the iris root, covering the trabecular meshwork, and forms a firm attachment to the prominent, anteriorly displaced Schwalbe's line. The transparent membrane is usually barely visible on slit-lamp or gonioscopic examination (Lines et al. 2002).
Optical coherence tomography (OCT) displays high resolution, cross-sectional images of the anterior segment by detecting changed optical reflections of different ocular microstructures converted to false colour images. These morphometric measurements provide precise information on the in vivo architecture of the anterior chamber. We performed multiple anterior segment B-scans using OCT to determine the cross-sectional anatomy in an eye with anterior segment anomalies secondary to ARA.
We report a 32-year-old, white woman with ARA with anterior segment anomaly. Her intraocular pressure was 35 mmHg OD and 45 mmHg OS. Slit-lamp examination revealed a clear cornea without breaks in Descement's membrane (Haab striae), but areas of iris hypoplasia and a posterior embryotoxon were observed. The fundi appeared normal except for the optic nerve heads, with increased cup : disc ratio of 0.9 OU. Gonioscopy disclosed a prominent posterior embryotoxon with adherent iris strands in both eyes. Images derived from OCT showed a bridging strand of trabecular tissue that appeared to arise from the anterior border of the iris root and follow the prominent Schwalbe's line (Figs 1 and 2). The subject had been born at term and no problems or exposure to toxic materials were recorded during her prenatal period. The patient had no additional systemic features of Axenfeld syndrome.
The trabecular meshwork develops around the 15th week of gestation, when the synthesis and secretion of extracellular matrix proteins begins. Axenfeld called this aberrant tissue ‘embryotoxon cornea posterius’ and described a white line in the posterior aspect of the cornea. The ring-like structure has adherent stands from the iris root, which traverse the filtrating iridocorneal angle, obstructing the outflow of aqueous humour. The almost transparent Barkan membrane probably consists of endothelial cells and is held responsible for a clotted angle and reduced aqueous outflow (Maul et al. 1980; Bakunowicz-Lazarczyk et al. 2001).
This is the first report to evaluate the trabecular meshwork in vivo by OCT in a patient with ARA. In our case, serial cross-sectional OCT scans assessed the anatomical morphology of the anterior segment, visualized the membrane obstructing the angle and confirmed previously published histological investigations. Optical coherence tomography provides precise information on the in vivo structure of the anterior segment, which is important to define the diagnosis and select appropriate treatment in congenital glaucoma.