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Boy Braaf, Koenraad Arndt Vermeer, Mattijs de Groot, Kari V Vienola, Johannes F de Boer; Fiber-based polarization-sensitive swept-source OCT of the human retina at 1 µm. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1626.
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© ARVO (1962-2015); The Authors (2016-present)
Polarization-sensitive OCT (PS-OCT) is a extension of standard OCT to measure tissue optical polarization properties which are known to give insight in the progression of several diseases. A fiber based PS-OCT instrument to image the retina is presented using a 1 µm wavelength swept-source and a novel method to correct for fiber-induced polarization distortions.
A high-speed fiber-based PS-OCT system was constructed based on a 1050 nm swept-source laser with an A-scan rate of 100 kHz. Two depth-multiplexed orthogonal polarization states simultaneously illuminated the sample, and polarization-sensitive detection was implemented to analyze the back-scattered light. A Jones matrix analysis method was developed to determine the double-pass phase retardation (DPPR) of the imaged tissues. This included a calibration against fiber-induced polarization distortions based on matrix diagonalization using the sample surface polarization state as a function of wavelength. The system operated at a sensitivity of 91.4 dB for a 1.5 mW power on the cornea. A healthy volunteer was imaged in the macula area and inferior to the optic nerve head (ONH). Averaging was used to suppress speckle noise in the DPPR images with a kernel of 3x7 pixels (h×w).
Figure 1 shows the results for imaging the macula, which demonstrates the low birefringent properties of the macula by a minimum amount of DPPR. Two locations in the center of the fovea are marked with arrows where Henle's fiber layer caused increased DPPR levels. Below the choroid two arrows mark an increase in DPPR that is caused by the birefringence of the sclera. Figure 2 shows increased DPPR inferior to the ONH at locations corresponding to the rim of the scleral canal (marked by arrows flanking the ONH pit), and the sclera (arrows lower right corner), which are both hard to identify in the intensity image.
The presented PS-OCT system measures phase retardation in tissues inside and below the retina that are known to be birefringent. This will be of specific interest in future studies to diseases that alter ocular tissue polarization properties during their progression, e.g. glaucoma or multiple sclerosis.
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