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Peripapillary rat sclera investigated in vivo with polarization-sensitive optical coherence tomography.

PURPOSE
To demonstrate polarization-sensitive (PS) optical coherence tomography (OCT) for noninvasive, volumetric, and quantitative imaging of the birefringent properties of the peripapillary rat sclera; to compare the findings from PS-OCT images to state-of-the-art histomorphometric analysis of the same tissues.


METHODS
A high-speed PS-OCT prototype operating at 840 nm was modified for imaging the rat eye. Densely sampled PS-OCT raster scans covering an area of ~1.5 × 1.5 mm centered at the papilla were acquired in the eyes of anesthetized male Sprague-Dawley rats. Cross-sectional PS-OCT images were computed, and fundus maps displaying the birefringent properties of the sclera were analyzed. Postmortem histomorphologic analysis was performed.


RESULTS
Polarization-sensitive OCT enables visualization of the polarization properties of ocular tissues in vivo. The birefringent characteristics of the rat sclera were quantitatively assessed. Scleral birefringence formed a donut-shaped pattern around the papilla with significantly increased values of 0.703 ± 0.089°/μm (i.e., 1.64 × 10(-3) ± 0.2 × 10(-3); mean ± standard deviation) and 0.721 ± 0.084°/μm (i.e., 1.68 × 10(-3) ± 0.2 × 10(-3)) at an eccentricity of 0.4 mm for the left and right eyes, respectively. Birefringent axis orientation maps revealed a ring-shaped distribution around the optic nerve. Postmortem PS-OCT micrographs provided access to retinal and scleral microstructure and were compared to standard histomorphologic analysis.


CONCLUSIONS
Polarization-sensitive OCT enables quantitative imaging of tissue polarization properties in addition to conventional OCT imaging based on reflectivity. In the rat sclera, in vivo PS-OCT provides access to volumetric mapping of birefringence. Scleral birefringence is associated with microstructural tissue organization. Therefore, PS-OCT should prove a valuable tool for the in vivo investigation of peripapillary sclera in glaucoma.