The morphology of angle dysgenesis assessed by ultrasound biomicroscopy and its relationship with glaucoma severity and mutant genes in Axenfeld-Rieger syndrome

BACKGROUND: Axenfeld-Rieger syndrome (ARS), a developmental disorder, involves anterior segment abnormalities and can lead to glaucoma. However, limited research has addressed the ultrasound biomicroscopy (UBM) characteristics of ARS. This study aimed to assess the anterior chamber angle features using UBM in ARS and determine their correlation with glaucoma severity and mutant genes. METHODS: UBM examination was conducted for 42 patients diagnosed with ARS and glaucoma. The morphology of the anterior chamber angle was classified into 6 types (type A, pure high iris insertion; type B, posterior embryotoxon; type C, iris process; type D, trabecular-iris synechia; type E, peripheral iridocorneal adhesion; type F, goniodysgenesis). Candidate genes were sequenced with next-generation sequencing. Correlations of clinical characteristics with angle dysgenesis types and mutant genes were analyzed. RESULTS: Among the 42 patients recruited, 6 eyes were excluded for poor quality UBM images or lack of glaucoma development. The remaining 78 eyes were categorized into 6 groups according to their dominant type of anterior chamber angle (>2 quadrants). There were statistically significant differences in onset age of glaucoma (P<0.001), untreated intraocular pressure (IOP) (P=0.016), vertical cup to disc ratio (P=0.001), and age at surgery (P<0.001) among the groups. Eyes in the type C and D groups developed glaucoma and underwent surgery at an earlier age, while eyes in the type B, E, and F groups developed glaucoma at a relatively later age. Eyes in type A group developed glaucoma and underwent surgery at the latest age, and had the lowest untreated IOP compared to the other groups. Patients with FOXC1 defects were more likely to have angle type B, type C, and type D (accounting for 93.8% of the total), whereas patients with PITX2 defects were more likely to have angle type A, type E, and type F (accounting for 92.1% of the total). CONCLUSIONS: UBM is powerful for evaluating the anterior segment abnormalities in ARS. Combined with genetic testing results, the morphological classification helps to assess the severity of glaucoma.