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Tomoko Asai, Yasushi Ikuno, Masahiro Akiba, Kohji Nishida; New Parameters Representing Peripapillary Morphology in Highly Myopic Eyes Using High-Penetration Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2152.
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© ARVO (1962-2015); The Authors (2016-present)
Since myopia is highly susceptible to the glaucoma at a given intraocular pressure (IOP), it is critical to investigate the morphological characteristics in these eyes. In order to assess the configurative profile around the optic nerve disc (ONH) in highly myopic eyes, we tested the new parameter in the circular peripapillary scan image from high-penetration optical coherence tomography (HP-OCT).
A total of 41 normal myopic eyes (refractive error greater than -6 diopters or axial length longer than 26mm) of 27 patients were examined with prototype HP-OCT (Topcon, Tokyo, Japan) at Osaka University Hospital. Circular peripapillary (3.4mm of diameter) HP-OCT images were taken and analyzed. Eyes with glaucoma were excluded. Retinal pigment epithelium (RPE) and chorio-scleral interface (CSI) were manually traced, and the mean vertical position of RPE/CSI line was calculated after dividing into 12 sectors. The scan started at horizontal nasal and always went up superior, temporal and inferior in a clockwise (left eye) or anticlockwise fashion (right eye). Average choroidal thickness (ChT) of 12 individual sectors was obtained. The vertical distance between a given sector and opposite site (namely peripapillary index: PPI) was also obtained. The PPI was always calculated by subtracting the temporal height from nasal height. Because there was 12 sectors, the PPI was 6 (sector 1-7, 2-8, 3-9, 10-4, 11-5, and 12-6). We investigated the profile of these parameters at each sectors, and looked for relationship to refractive error, axial length, and tilted disc index (TDI), minor/major axis ratio of ONH, which was obtained from fundus photographs.
Mean ChT was significantly different among 12 sectors (P<0.05). ChT was thickest at the sector 3 (135μm), and thinnest at sector 7 (60μm). PPI was also significantly different between 6 pairs (P<0.0001). The PPI was the largest at sector 2-8, and the smallest at sector 10-4. PPIs from superonasal 3 sectors were significantly correlated with TDI (segment 1-7 and 3-9; P<0.05, segment 2-8; P<0.01), however not inferonasal 3 sectors. PPIs of segment 2-8 and 3-9 were significantly correlated with axial length (P=0.05), but TDI not (P= 0.68).
The area around ONH is tilted especially at the inferotemporal area, which is agreeable with a finding that choroidal thinning is most prominent in this area. The new parameter, PPI of superonasal area is associated with the degree of tilted disc, and also reflects myopic axial length elongation.
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