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Rebecca Lindsay, John P Kelly, Avery H Weiss; Aniridia and reduction in nerve fiber layer: Quantitative analysis using SD-OCT. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3382.
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The association between PAX6 mutations, aniridia and optic nerve hypoplasia (ONH) has been well documented. We report 4 cases of pediatric patients with mutations in PAX6, aniridia and reduction in nerve fiber layer confirmed and quantified with spectral domain OCT (SD-OCT).
Patients were children (17 months to 12 years age) with isolated PAX6-associated aniridia (3 patients confirmed by PAX6 gene testing; 1 with PAX6 mutation presumed on the basis of dominant inheritance). Images of the fovea and optic nerves were obtained using SD-OCT (Spectralis, Heidelberg Engineering) utilizing automated eye tracking. In two patients, sectoral retinal nerve fiber layer (RNFL) thickness was determined using the Spectralis circular RNFL scan centered on the optic disc. In the remaining 2 subjects, RNFL thickness was determined manually from line scans owing to nystagmus. In the latter 2 cases, distances from the optic nerve center were corrected for refractive error and results were plotted with the normative RNFL data. RNFL data from 5 children with ONH were used as a comparison. The diameter of the optic canal (distance between Bruch's membrane) was estimated by horizontal line scans through the middle of the optic nerve.
All aniridics had annular deficiencies of the central iris, foveal hypoplasia without an anatomical pit, and nystagmus. None of the aniridics had glaucoma. There were global losses of the nerve fiber layer within the maculopapular bundle as well as the remaining quadrants (microns below norms, temporal = 29, superior = 25, nasal = 24, inferior = 48). Overall, RNFL thickness was similar between subjects with aniridia and ONH at all quadrants. The optic canals ranged from 1360 to 1700 microns in aniridia whereas the range was 740 to 1274 microns in ONH.
We show RNFL thickness in the maculopapular bundle is decreased in aniridia, which is expected from isolated foveal hypoplasia. However, there is a reduction across all RNFL quadrants, particularly the infero-nasal quadrant. The optic canal diameter is normal in this subset of patients but is small in ONH, suggesting that, in a subset of patients, the pathogenic mechanisms underlying hyoplasia of the RNFL in aniridia and ONH are different.
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