Axenfeld-Rieger syndrome: a theory of mechanism and distinctions from the iridocorneal endothelial syndrome.

Twenty-four patients with the diagnosis of Axenfeld's anomaly or Rieger's anomaly or syndrome were the subjects of a clinical study, which included specular microscopy of the corneal endothelium in 16 cases and fluorescein angiography of the iris in 5. Histopathologic material was obtained from ten eyes of eight of these patients (one enucleated eye and nine trabeculectomy specimens) and was studied by light and electron microscopy. The overlapping of ocular and nonocular defects in these patients prevented subclassification according to traditional criteria. Any attempted subdivision appears to have minimal clinical value, and a single classification for the disease spectrum is believed to be more practical. The collective term Axenfeld-Rieger (A-R) syndrome is proposed. A theory of mechanism for the ocular features of the A-R syndrome is postulated which involves a developmental arrest, late in gestation, of tissues derived from neural crest cells. This leads to retention of primordial endothelial tissue on the iris and across the anterior chamber angle, which produces the iridic changes and the peripheral tissue strands. Continued contraction of these membranes after birth explains the progressive changes noted in some patients. This primordial endothelium also produces excessive and atypical basement membrane, especially near the corneolimbal junction, which accounts for the prominent Schwalbe's line. The secondary glaucoma results from arrested development of the anterior chamber angle structures, characterized by incomplete maturation of the trabecular meshwork and Schlemm's canal and a high insertion of the iris. The ICE syndrome may be confused with the A-R syndrome on the basis of certain clinical and histopathologic similarities. Based on available evidence, however, it is postulated that the two entities are distinctly separate, in that the fundamental defect in the ICE syndrome is believed to be an abnormality of the corneal endothelium with secondary proliferation of a tissue layer over the anterior chamber angle and iris, while the A-R syndrome is thought to represent a developmental arrest with retention of a primordial membrane and other developmental defects.