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E. Gotzinger, M. Pircher, B. Baumann, C. Vass, A. Luksch, C. Hitzenberger; Retinal Nerve Fiber Layer Birefringence of Healthy and Glaucomatous Eyes Measured With Polarization Sensitive Spectral Domain OCT. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3762.
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© ARVO (1962-2015); The Authors (2016-present)
To measure the birefringence of the retinal nerve fiber layer around the optic nerve head of healthy and glaucomatous eyes and to compare the results.
A polarization sensitive spectral domain optical coherence tomography (PS-SD-OCT) system is used to measure the birefringence (retardation per unit depth) of the retinal nerve fiber layer (RNFL) of normal and glaucomatous eyes. The instrument records three parameters simultaneously: intensity, phase retardation and optic axis orientation. Recording time for a full 3D data set is 3 seconds. From these 3D datasets the birefringence around the optic nerve head was calculated. 8 normal eyes and 8 glaucomatous eyes were measured with this instrument.
From the measured 3D datasets 100 concentric circles around the nerve head have been extracted and the birefringence of the RNFL was calculated within this area. In case of the healthy eyes the mean value of the single pass birefringence (°/µm) around the optic nerve head was 0,061 +/- 0,008, and in case of the glaucomatous eyes the mean value was 0,041 +/- 0,006 (mean +/- SD).Statistical analysis (t-test) showed that this difference is highly significant (p=0,000082). Similar analysis was carried out in the superior and in the inferior quadrant. Superior quadrant birefringence was 0,084 +/- 0,015 in normal eyes and 0,051 +/- 0,016 in glaucomatous eyes, while inferior quadrant birefringence was 0,062 +/- 0,009 (normal) and 0,039 +/- 0,007 (glaucoma). These results show again highly significant difference (p=0,0012 and p=0,00018, respectively).
PS-SD-OCT combines the capability of OCT to provide depth information with the polarization sensitivity of scanning laser polarimetry (SLP). Therefore, it can not only measure retardation, as SLP, and thickness as OCT, but can also directly measure birefringence of the RNFL, i.e. retardation per unit depth, a quantity not measurable by any other technique. Circumpapillary RNFL birefringence in glaucomatous eyes differs significantly from RNFL birefringence in healthy eyes.The capability of PS-OCT to provide quantitative data on RNFL birefringence in the nerve head region might improve glaucoma diagnosis and follow up.
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