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E. Gotzinger, M. Pircher, B. Baumann, H. Resch, C. Vass, C. K. Hitzenberger; Comparison of Retinal Nerve Fiber Layer Birefringence and Thickness of Healthy and Glaucoma Suspect Eyes Measured with Polarization Sensitive Spectral Domain OCT. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5823.
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© ARVO (1962-2015); The Authors (2016-present)
To measure the birefringence (retardation per unit depth) and thickness of the retinal nerve fiber layer around the optic nerve head of healthy and glaucoma suspect eyes and to compare the results.
A polarization sensitive spectral domain optical coherence tomography (PS-SD-OCT) system is used to measure the thickness and birefringence of the retinal nerve fiber layer (RNFL) of normal and glaucoma suspect eyes. From the acquired 3D datasets the birefringence and thickness around the optic nerve head was calculated. (100 concentric circles around the nerve head have been extracted and the birefringence and thickness of the RNFL was calculated within this area). 8 normal eyes and 12 glaucoma suspects were measured with this instrument.
In case of the healthy eyes the mean value of the single pass birefringence (°/µm) around the optic nerve head was 0.058 +/- 0.003, and in case of the glaucoma suspects the mean value was 0.039 +/- 0.007 (mean +/- SD).Statistical analysis (t-test) showed that this difference is highly significant (p=0.0000031). The optical mean RNFL thickness (µm) of the healthy eyes was 169 +/- 16 and of the glaucoma suspects 152+/-14 (p=0.019). 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 0.041 +/- 0.011 in glaucoma suspect eyes, while inferior quadrant birefringence was 0.059 +/- 0.007 (normal) and 0.039 +/- 0.009 (glaucoma suspects). These results show again highly significant difference (p=0.00000057 and p=0.00014, respectively). Superior quadrant optical thickness was 197 +/- 23 in normal eyes and 172 +/- 18 in glaucoma suspect eyes, while inferior quadrant optical thickness was 174+/- 15 (normal) and 155 +/- 20 for glaucoma suspects (p=0.015 and P=0.04, respectively) .
PS-SD-OCT measures the thickness and birefringence of the RNFL. Mean RNFL thickness of glaucoma suspect eyes is reduced (compared to healthy eyes) by 10% (superior: 12.7%, inferior: 10.9%), whereas mean RNFL birefringence is already reduced by 33% (superior: 51.7%, inferior: 34%). RNFL birefringence might be an early indicator for glaucoma and therefore might improve early glaucoma diagnosis.
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