Polarization-sensitive optical coherence tomography (PS-OCT) is known to be advantageous because of its additional tissue-specific contrast of the anterior eye. So far, this advantage has been shown only qualitatively. We evaluate the improved visibility afforded by 3-D PS corneal and anterior eye segment OCT (PS-CAS-OCT) in visualizing the trabecular meshwork (TM) based on statistical evidences. A total of 31 normal subjects participated in this study. The anterior eye segments of both the eyes of the subjects are scanned using a custom-made PS-CAS-OCT and the standard-scattering OCT (S-OCT) and polarization-sensitive phase-retardation OCT (P-OCT) images are obtained. Three graders grade the visibility of the TM using a four-leveled grading system. The intergrader agreement, intermodality differences, and interquadrant dependence of visibility are statistically examined. All three of three combinations of graders show substantial agreement in visibility with P-OCT (ρ = 0.74, 0.70, and 0.68, Spearman's correlation), while only one of three shows substantial agreement with S-OCT (ρ = 0.72). Significant dependence of the visibility on the modality (S-OCT versus P-OCT) and quadrants are found by the analysis of variance. A subsequent Wilcoxon signed-rank test reveals significantly improved visibility. PS-CAS-OCT may become a useful tool for screening angle-closure glaucoma.
A tissue discrimination algorithm of polarization sensitive optical coherence tomography (PS-OCT) based on optical properties of tissue was developed. We calculated three dimensional (3D) feature vector (intensity, extinction coefficient, birefringence) obtained by PS-OCT. The tissue types of each pixel were discriminated according to positions of the feature vectors in 3D feature space. This algorithm was applied for discrimination of human anterior eye chamber. Conjunctiva, selera, trabecular meshwork (TM), cornea and uvea were well separated in the 3D feature space and discriminated in good contrast.
Adaptive optics scanning laser ophthalmoscope with 1-micrometer band probe is presented. The residual wavefront error
was less than 0.02 with in vivo human eye. Photoreceptor cones are visualized at the eccentricity up to 10 degrees.
An application of swept-source polarization sensitive optical coherence tomography (PS-OCT) to anterior eye is presented. The image properties of anterior eye segments in PS-OCT images are discussed. The ability of PS-OCT to visualize trabecular meshwork is evaluated. For this evaluation, 25 normal subjects were involved. The visibility of trabecular meshwork in PS-OCT images of the subjects were scored by 2 graders. The grading score were then statistically analyzed. This analysis shows a statistically significant improvement of the visibility of trabecular meshwork in PS-OCT images against conventional intensity OCT images. A birefringent artifact appeared in anterior eye segment OCT image is also discussed.
Polarization properties of anterior segment disorders of the eyes were evaluated using a fiber-based
polarization-sensitive Fourier-domain optical coherence tomography (PS-FD-OCT). The light source is a
superluminescent diode with a central wavelength of 840 nm, and bandwidth of 50 nm. Synchronized two
line-CCD cameras allow high-speed measurement of birefringence of retina (line rate 27.7 kHz), and the
sensitivity of the system is 100.7 dB. Birefringence of the optical fiber was compensated with the surface
reflection. Phase retardation and orientation of the birefringence were measured with a Jones matrix based
algorithm. The phase retardation map of the anterior segment was visualized as a depth-resolved
three-dimensional image in addition to the conventional cross sectional OCT image. In the polarization
image of the normal eye, striking polarization change was observed at the sclera. In the eyes with necrotizing
scleritis, abnormal thinning of the sclera could be confirmed. In the eyes after filtering glaucoma surgery,
polarization change in the conjunctiva due to the abnormal fibrosis after surgery could be observed.
PS-FD-OCT is an effective tool to understand the polarization properties of different types of pathological
changes in the anterior segment of the eye.
A two- and three- dimensional swept source optical coherence tomography (SS-OCT) system is demonstrated. This system uses 1.3 &mgr;m probe band, posesses a depth resolution of 14 &mgr;m, and operated at a sensitivity of 100 dB. This SS-OCT is capable of realtime display of two-dimensional OCT, and can take three-dimensional OCT with the measurement time of 2 s.
28 cases of 25 patients including 6 types of corneal diseases, 4 types of uveal diseases, 1 type of scleral disease and 3
types of glaucoma surgery are examined by this SS-OCT.
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