Abstract
Purpose: :
To develop novel SDOCT technology to quantitatively measure the degree of polarization of retinal layers and use this information to unambiguosuly segment the retinal pigment epithelium in SDOCT images.
Methods: :
A single camera high speed polarization sensitive spectral domain OCT (PS-SDOCT) system was developed. We describe a novel phase unwrapping method to extract the total reflectivity, accumulative retardance and fast axis orientation of the retinal nerve fiber layer (RNFL). We describe two methods to obtain the degree of polarization (DOP) of the retinal layers, a first method based on Stokes vectors analysis and a second based on multiplication of the standard deviation of the retardance and the fast axis orientation. The RPE is segmented based on the DOP.
Results: :
Testing of the PS-SDOCT system with a waveplate indicates that the average error for retardance was 3.2°+/-2.3°, and of fast axis orientation was 1.2°+/-0.7° which in the fast axis case is an order of magnitude better performance than other contemporary PS-SDOCT systems. Three normal eyes were measured with this instrument. The peak value of the single pass birefringence (°/µm) near the optic nerve head was 0.17 for a healthy eye in which the RNFL thickness was 120 µm. Quantitative mapping of the DOP of the retinal layers indicates that the retinal pigment epithelium (RPE) appears as light, intermediate and strong depolarization interleaving bands. The most depolarizating location is close to the foveal center. The DOP of the RPE within the range of 1.6mm around foveal center was 5db higher than in other areas. The RPE was successfully segmented based on the DOP .The retinal DOP mapping is illustrated below:
Conclusions: :
We demonstrate quantitative mapping of the DOP of the retinal layers simultaneously using the standard deviation of retardance, fast axis orientation and Stokes vectors methods. The performance of the fast axis orientation 1.2°+/-0.7° is ~10 times more accurate than in contemporary PS-SDOCT. The accurate mapping of the DOP of the retinal layers and measurement of retardance of RNFL could improve diagnosis of glaucoma and retinal degenerative diseases in clinical applications.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: non-clinical • retinal pigment epithelium