Early Phenotypic Features of Aniridia-associated Keratopathy and Association with PAX6 Coding Mutations

Purpose: To investigate corneal phenotype in aniridia-associated keratopathy (AAK) including its earliest manifestations, in relation to PAX6 mutational status.

Methods: 46 subjects (92 eyes) with congenital aniridia from a German registry were examined using slit lamp biomicroscopy, anterior segment optical coherence tomography, contact esthesiometry and in vivo confocal microscopy. Cytogenetic analysis was conducted by Sanger sequencing of PAX6 exons and/or MLPA analysis. Measured parameters included AAK grade, distance-corrected visual acuity (DCVA), central corneal thickness (CCT), corneal sensitivity, subbasal nerve density, mature dendritic cell (DC) density and corneal epithelial phenotype.

Results: 46 subjects (age range: 1-64 years) were examined, including 23 (50%) children under the age of 18. Five subjects (11.1%) with absent PAX6 coding mutation (non-PAX6 cases) had mild AAK (Grade 0-1) into the fourth decade of life and maintained corneal epithelial phenotype, greater subbasal nerve density (16.8 mm/mm vs. 3.58 mm/mm, P = 0.01) and better corneal sensitivity (41 ± 11 mm vs. 28 ± 12 mm, P = 0.03) relative to those with PAX6 coding mutations. In five subjects, corneal endothelial cell density ranged from 3245 to 4399 cells/mm. Independent of mutational status, an increased CCT, over tenfold increased mature DC density and reduced corneal sensitivity characterized all subjects.

Conclusions: PAX6 coding mutations influence AAK phenotype and progression from the earliest stages of life. A minimal keratopathy present in 100% of congenital aniridia cases is independent of the specific mutation and consists of increased corneal thickness, reduced touch sensitivity, and increased ocular surface immune activity.