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Yongjoo Kim, Jang-Ryul Park, Tae Jin Park, Jeeyun Ahn, Se Joon Woo, Kyu Hyung Park, Wang-Yuhl Oh; High-Speed Multi-Functional Retinal Optical Frequency Domain Imaging. Invest. Ophthalmol. Vis. Sci. 2014;55(13):219.
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OCT has been used as a powerful tool for retinal imaging. However, conventional OCT image only provides structural information of the retina and there is demand for functional extensions of OCT technique for the tissue-specific visualization of the retina. The most promising modalities are polarization-sensitive and Doppler imaging for birefringent retinal layers or blood vessels. To acquire additional information of the retina, we developed a high-speed multi-functional optical frequency domain imaging (OFDI) additional to the intensity imaging that provides for both polarization-sensitive and Doppler imaging.
An eye of healthy volunteer was imaged with OFDI system. Novel short-cavity wavelength-swept source was developed as a light source with A-line rate of 230 kHz centered at 1050 nm. For polarization-sensitive imaging, polarization of the light source is modulated so that it alternates between a pair of states that are perpendicular to each other on the Poincare sphere. For Doppler imaging, circular-variance based algorithm was used to observe vasculature of the retina.
Retinal imaging was conducted on the area of 3.5 mm x 3.5 mm around the foveal region (Fig. 1). Fig. 2(a) shows phase retardation image. The phase retardation does not change over entire retinal layer above choroidal layer (displayed as deep blue), while it increases at the border of choroid and sclera layer (light blue). Fig. 2(b) represents DOPU (degree of polarization uniformity) image. The DOPU value at the RPE (indicated as white arrows) is notably lower than upper layers showing clear discrimination between RPE and other layers. Fig. 2(c) shows en-face OCT angiography reconstructed from corresponding Doppler OCT data. Microvasculature of retina is well visualized.
We demonstrated high-speed multi-functional retinal OFDI system that is capable of performing both polarization-sensitive and angiographic imaging. The multi-functional imaging system allows better understanding of the retina by providing additional contrast for RPE and choroid-sclera segmentation. Moreover, the depth-resolved OCT angiography shows great potential for diagnosing diseases associated with retinal vasculature modification.
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