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Rebecca Mastey, Katie M Litts, Margaret R Strampe, Christopher S Langlo, Emily J Patterson, Melissa A Wilk, Joseph Carroll; Interocular symmetry and repeatability of foveal outer nuclear layer thickness in congenital achromatopsia. Invest. Ophthalmol. Vis. Sci. 2017;58(8):6005. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the interocular symmetry and repeatability of foveal outer nuclear layer (ONL) thickness measurements in patients with congenital achromatopsia (ACHM).
Sixty-two subjects with ACHM (34 M, 28 F) and 14 subjects with normal vision (4 M, 10 F) were recruited. Horizontal line scans (1,000 A-scans, 80-100 repeated B-scans) were acquired using Bioptigen optical coherence tomography (OCT). For each eye, B-scans were registered and averaged to create a single image. A longitudinal reflectivity profile (LRP) was obtained at the fovea for each image using custom software.1 ONL thickness was measured between the inner limiting membrane and the external limiting membrane (ELM) in cases of complete foveal excavation, or between the posterior boundary of the outer plexiform layer and the ELM in cases of foveal hypoplasia.2 Three LRP estimates of ONL thickness were obtained for each subject to assess repeatability.
ONL thickness did not differ between eyes in ACHM (p=0.19) or control subjects (p=0.09), consistent with high interocular symmetry. The mean ± SD ONL thickness was 75.0 ± 17.2 µm for ACHM subjects and 109.4 ± 16.5 µm for normal subjects. Despite this significant difference (p<0.0001) there was substantial overlap between the two groups (Figure). Excellent intra-grader repeatability was observed with an ICC of 0.922 for ACHM subjects and 0.988 for controls. The measurement error (defined as 1.96*within-subject SD) was 10.1µm for ACHM and 3.7µm for controls.
Foveal ONL thickness is reduced in ACHM, consistent with previous reports2 and indicative of disrupted cone structure. Importantly, our measurements show excellent repeatability. Our observation of ONL symmetry in ACHM supports the use of the contralateral eye as a control for trials in which only one eye is treated. Perifoveal measures of ONL thickness will need to account for the presence of the Henle fiber layer, which is difficult due to the severe nystagmus in some subjects with ACHM.1Wilk PMID:278878882Sundaram PMID:24148654
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Foveal ONL thickness (OD) for normal and ACHM subjects (black bar represents the mean and error bars represent ± 2 SDs). While the ONL is, on average, significantly thinner in ACHM compared to controls (p<0.0001), there is considerable overlap between the two groups.
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