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Mervyn George Thomas, Viral Sheth, Wai-Man Chan, Caroline Andrews, Elizabeth C Engle, Irene Gottlob; High Resolution in-vivo Imaging in Patients with PAX6 Mutations. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6413.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies investigating retinal morphology in patients with PAX6 mutations have been using time domain OCT, which has lower resolution and scanning speeds thus limiting imaging in patients with nystagmus. We aimed to investigate the retina and iris using spectral domain OCT (SD-OCT) in patients with PAX6 mutations.
Patients presenting with autosomal dominant nystagmus or singletons with infantile vertical nystagmus (n=18) underwent sanger sequencing to identify PAX6 mutations. SD-OCT (Copernicus HR, 3µm axial resolution) was used to image the fovea, parafovea, optic nerve head and iris. We used a 3D scanning program with a 7x7mm scanning window (AxB; 743x75). Tomograms were segmented and thickness measurements were derived using imageJ. We compared the thickness measurements against controls (n=50).
PAX6 mutations were identified in 15/18 patients. In 3/15 patients we were not able to obtain good quality scans due to cataract or corneal opacity. All 12 patients with PAX6 mutations had foveal hypoplasia. 7/12 patients had a rudimentary foveal pit, while there was no pit in 5/12 patients. The foveal pit was significantly shallower (p<0.0001) while the central macular thickness was significantly increased in patients with PAX6 mutations (p<0.0001). The outer segment was significantly smaller (p<0.0001) in the patients. The ganglion cell layer (GCL) and nerve fibre layer (NFL) thickness was significantly decreased in PAX6 patients (p<0.0001). There was a significant positive correlation between GCL and NFL thickness (r=0.73, p=0.004). The iris phenotypes were variable ranging from normal iris (c.227C>G) to aniridia (c.917_1184del). The milder iris phenotypes included transillumination defects and iris hypoplasia. We were able to visualise the range of morphological abnormalities of the iris using anterior segment OCT. Mutation within the linker subdomain (p.P76R) was associated with the mildest phenotype (normal iris with grade 1 foveal hypoplasia).
We have systematically investigated the retinal and iris phenotypes associated with PAX6 mutations using SD-OCT. We show the spectrum of foveal hypoplasia associated with PAX6 mutations. The NFL thinning observed in patients with PAX6 mutations are related to the GCL loss. For the first time we are able to demonstrate the use of anterior segment OCT to visualise the range of iris phenotypes.
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