In Vivo Assessment of Retinal Phenotypes in Axenfeld-Rieger Syndrome

Abstract

Purpose: Axenfeld-Rieger syndrome (ARS) is characterized by ocular anomalies including posterior embryotoxon, iridocorneal adhesions, corectopia/iris hypoplasia, and developmental glaucoma. Although anterior segment defects and glaucoma contribute to decreased visual acuity, the role of potential posterior segment abnormalities has not been explored. We used high-resolution retinal imaging to test the hypothesis that individuals with ARS have posterior segment pathology.

Methods: Three individuals with FOXC1-ARS and 10 with PITX2-ARS completed slit-lamp and fundus photography, optical coherence tomography (OCT), OCT angiography, and adaptive optics scanning light ophthalmoscopy (AOSLO). Quantitative metrics were compared to previously published values for individuals with normal vision.

Results: All individuals demonstrated typical anterior segment phenotypes. Average ganglion cell and inner plexiform layer thickness was lower in PITX2-ARS, consistent with the glaucoma history in this group. A novel phenotype of foveal hypoplasia was noted in 40% of individuals with PITX2-ARS (but none with FOXC1-ARS). Moreover, the depth and volume of the foveal pit were significantly lower in PITX2-ARS compared to normal controls, even excluding individuals with foveal hypoplasia. Analysis of known foveal hypoplasia genes failed to identify an alternative explanation. Foveal cone density was decreased in one individual with foveal hypoplasia and normal in six without foveal hypoplasia. Two individuals (one from each group) demonstrated non-foveal retinal irregularities with regions of photoreceptor anomalies on OCT and AOSLO.

Conclusions: These findings implicate PITX2 in the development of the posterior segment, particularly the fovea, in humans. The identified posterior segment phenotypes may contribute to visual acuity deficits in individuals with PITX2-ARS.

Figure 1.

Anterior segment images illustrating features of ARS in imaged individuals. (A–M) Slit-lamp images demonstrating typical ARS features in all individuals, including iridocorneal adhesions (arrow in A), posterior embryotoxon (arrow in D), iris hypoplasia (asterisk in E), and corectopia (arrow in K). Pigment deposits in the cornea (arrow in G1) and lens opacity (asterisk in K1) were also noted in some individuals. Individual number is indicated in the upper right corner of each image. Both eyes are shown for individuals with asymmetric iris phenotypes. Surgical history includes glaucoma surgery in the eyes pictured in B, D, E, F1, H1, K, and K1 and cataract surgery as well as corneal transplant in H1 and I.

Figure 2.

Posterior segment images of selected individuals. (A–F) In individual 2, fundus photography (A) demonstrated peripapillary atrophy and linear streaks across the retina with corresponding focal disruptions of the ellipsoid zone band on OCT (B, arrow) and linear regions of abnormal photoreceptor pattern by AOSLO (C, dashed line). In individual 5, fundus photography (D) revealed subretinal deposits along the fovea with irregularities in the inner and outer segment junction on OCT (E, bracket) and patchy regions of abnormal photoreceptor pattern on AOSLO with several outlined with dashed lines (F). Scale bars: 250 µm.

Figure 3.

Foveal hypoplasia in PITX2-ARS. (A–E) OCT images from 15-year-old female with no vision-limiting pathology (A, control) and individuals 4 (B), 6 (C), 8 (D), and 13 (E) displaying grade 1b foveal hypoplasia. The arrow in A indicates the location of the fovea. Scale bar: 100 µm in each direction for all images.

Figure 4.

Foveal comparisons. (A). Foveal pit images showing variability among non-hypoplastic foveal pits. Largest (individual 1), intermediate (individual 7), and smallest (individual 9) non-hypoplastic pit images were chosen. (B, C) Plotting of foveal pit depth and volume demonstrates a statistically significant decrease in both metrics compared to normal controls for PITX2-ARS (blue symbols) but not FOXC1-ARS (yellow symbols). The normal range from control individuals is indicated by black lines in B and C. The symbol assigned to each individual is indicated in the lower left corner.

Figure 5.

OCT Angiography. (A–D) OCTA images demonstrate normal FAZ in individual 7 and a fragmented FAZ in individuals 6, 8, and 13, all of whom showed a foveal hypoplasia phenotype (Figure 3). Scale bar: 500 µm (all images).

Figure 6.

Cone mosaic analysis. Cone density (A, B) and spacing (C, D) were determined from AOSLO images from individuals with PITX2-ARS (blue symbols) and FOXC1-ARS (yellow symbols) along both the superior (A, C) and temporal (B, D) eccentricity. Only individual 6 (with foveal hypoplasia) had values consistently outside the normal range. The symbol assigned to each individual is indicated and consistent with Figure 4 (but AOLSO data are only available for a subset of participants).