Contrasting Foveal Specialization in Disorders Associated with Foveal Hypoplasia

Abstract

Purpose: While foveal specialization has been well characterized in albinism, less is known regarding foveal morphology in other disorders associated with foveal hypoplasia. Here we sought to quantify foveal specialization in patients with aniridia or a history of premature birth using spectral domain optical coherence tomography (SD-OCT) and adaptive optics scanning light ophthalmoscopy (AOSLO), and compare these findings to those of patients with albinism.

Methods: Subjects with a diagnosis of albinism (n=5), aniridia (n=3), or a history of premature birth (n=3, birth was between 25 and 30 weeks’ gestation) were recruited for this study. Volumetric SD-OCT scans of the macula were acquired, and custom MATLAB software was used to derive estimates of foveal pit depth, diameter, and volume. Additionally, high-resolution linear SD-OCT scans were acquired and manually segmented to obtain measurements of relative foveal cone inner and outer segment (IS and OS, respectively) length. Images of the photoreceptor mosaic and foveal avascular zone (FAZ) were acquired using AOSLO. When possible, cone density was measured using a semi-automated cone counting program, and FAZ area and diameter were measured using semi-automated segmentation.

Results: Despite having reduced FAZ areas, all 3 subjects with a history of premature birth displayed normal foveal pit metrics, normal foveal cone OS elongation, and normal cone packing. Consistent with previously reported results from 32 subjects with albinism and the additional 5 subjects reported here, the subjects with aniridia had variable OS lengthening. Clear evidence of cone packing was seen in one subject with aniridia, though due to the presence of severe nystagmus, it was not possible to quantify cone density in the remaining two subjects.

Conclusions: Contrary to previous observations in patients with a history of premature birth, our subjects displayed normal foveal specialization. Further work contrasting foveal specialization across these disorders may be useful to better understanding normal foveal development. While previous work from our group has shown that it is possible to obtain high quality images in patients with nystagmus, AOSLO hardware improvements and some form of eye tracking are needed to enable imaging of patients with severe nystagmus, such as that seen in aniridia.

Keywords: 497 development • 585 macula/fovea • 648 photoreceptors