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F. Jaillon, S. Makita, M. Miura, Y. Yasuno; Choroid Contrast Enhancement by Combining 1-Micron SD-OCT and Robust Mirror Image Removal. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2505. doi: https://doi.org/.
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Spectral domain optical coherence tomography (SD-OCT) is an appropriate modality to image the human posterior eye. Recently 1-µm wavelength probe light has been introduced to enable a better contrast of deep posterior regions such as choroid. SD-OCT is known to have its maximum sensitivity at a particular depth, so called zero-delay depth (ZDD). However, ZDD cannot be utilized for OCT imaging, because this is where an artifact, so called mirror image, overlaps with the real OCT image. This paper aims at demonstrating high-contrast and high-penetration structural imaging of choroid by using our new 1-µm high-penetration SD-OCT (HP-OCT) which is capable of eliminating the mirror image.
Ten eyes without marked posterior disorders, 1 eye of polypoidal choroidal vasculopathy (PCV) and 1 eye of age-related macular degeneration (AMD) were examined by HP-OCT. The 2 pathologic eyes were also examined by SD-OCT with a standard wavelength of 830 nm for a comparison purpose. HP-OCT has a central wavelength of 1.02 µm, a depth resolution of 4.3 µm in tissue and a measurement speed of 47,000 depth scans/sec. The 1-µm probe allows deeper penetration. The phase of an OCT reference beam is modulated parabolically in time. This newly introduced modulation mechanism eliminates the mirror image and enables wide depth range imaging. This method is not disturbed by sample motions, while previously demonstrated mirror image removal method is highly negatively affected by the motion. This new method enables a wide depth range of 3.6 mm, high-sensitivity, deep penetration and subsequently high contrast imaging of the choroid.
In HP-OCT images, the chorio-scleral interface was visible with 8 of 10 normal eyes. In the case of the PCV eye, hyperscattering mass located under pigment epithelial detachment was more highly contrasted in HP-OCT images than those of 830 nm. In the case of the AMD eye, enhanced contrast of choroid situated under hyperscattering fibrin is also observed.
The proposed combination of 1-µm HP-OCT with mirror image elimination enhances the visibility of chorio-scleral interface. Moreover compared to 830 nm system, it was shown that, in the case of pathologic eyes, the structures beneath retinal pigment epithelium possessed very high contrast.
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