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Abstract
Glaucoma is complex ophthalmic pathology that affects the retinal nerve fiber layer (RNFL) and results in partial or total vision loss. It is the second leading cause of blindness worldwide. It has been demonstrated that a decrease in RNFL thickness is directly related to the onset of glaucoma. As glaucoma progresses the RNFL axons die and the layer thins. Up to 40% of the axons can be lost before any visual field loss is detected by perimetry, the gold standard for glaucoma diagnosis. Therefore, an accurate measurement of RNFL thickness would be extremely useful for glaucoma diagnosis and follow up.
This dissertation presents a new optical imaging technique called polarization sensitive optical coherence tomography (PSOCT) and assesses its performances to measure the RNFL thickness. The principle of operation for PSOCT is similar to ultrasound B mode imaging and provides longitudinal cross-sectional images of tissue with a spatial resolution in the order of 15μm. The depth-resolved polarization state of light backreflected from the sample is determined by computing the Stokes parameters, which facilitates tissue birefringence imaging. Because the RNFL is the only birefringent layer in the retina, PSOCT provides a contrast image of this layer.
A PSOCT system was designed, constructed and calibrated. In vivo and ex vivo images were acquired in seven rabbit eyes and one monkey eye. A birefringent layer was observed in the most anterior part of the retina corresponding to the RNFL. The thickness of this layer is in good agreement with the RNFL thickness measured with histology.
Also, PSOCT images of the rabbit and monkey corneas were acquired to determine the effect of corneal birefringence on polarization state of light incident on the retina and to assess the structural organization of collagen fibrils in the corneal stroma. Rabbit corneal images showed significant variations in the birefringence of the corneal stroma between subjects and within a sample.
