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Thomas Klein, Wolfgang Draxinger, Wolfgang Wieser, Aljoscha Neubauer, Lukas Reznicek, Anselm Kampik, Robert Huber; Ultrawide-field choroidal thickness and structure map created with MHz-OCT. Invest. Ophthalmol. Vis. Sci. 2013;54(15):393.
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© ARVO (1962-2015); The Authors (2016-present)
To study the three dimensional choroidal thickness and choroidal structure over more than 50° field of view, using a single ultrawide-field OCT dataset.
We used a custom swept-source OCT device with an ultrahigh axial line rate of 1.68MHz, which is achieved with a Fourier-domain mode-locked laser source. Together with a center wavelength of 1060nm for increased sample penetration, densely-sampled ultrawide-field 3D datasets of the retina and choroid can be acquired in short time. Datasets consisting of 1088x1088 A-scans spanning ~55° field of view were acquired in 0.85s. The positions of RPE and chorioscleral border were determined manually by a trained observer in a subset of the 1088 B-scans. 3D Interpolation was performed between these points to create thickness (optical path) and intensity (structure) maps.
The short acquisition time yielded almost distortion-free 3D OCT datasets of healthy volunteers (10 eyes). Thickness varied considerably over the posterior pole in all subjects. For instance, in a subject with slight myopia (-1dpt), the outer superior choroid had the largest thickness of up to 560µm, which was about two times higher than the average thickness of 245µm. The mean thickness of the outer nasal area was smaller than that of other areas, with a minimum thickness of only 116µm. Hence thickness varies about a factor of five over the imaged area. In addition to the thickness map, the structure of the choroid can be visualized with an superimposed en-face visualization projection of the segmented 3D Data (see image).
Using MHz axial line rates and a central wavelength of 1060nm, ultrawide-field thickness and structure maps of the choroid can be created out of a single 3D OCT dataset acquired in less than a second. Our results suggest that choroidal thickness varies considerably over the posterior pole. Wide-field thickness and structure maps may allow for a more comprehensive evaluation of the choroid.
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