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H. Luo, J. Schwiegerling, E. Dereniak, T. Tkaczyk; Snapshot Retinal Imaging Polarimeter. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4252.
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To develop a retinal imaging system that captures the complete polarization state of the retinal nerve fiber layer in a single snapshot. The polarization state is directly proportional to the retinal nerve fiber layer thickness. The long-term goal of this system is to provide screening for early retinal changes associated with glaucoma.
We have retrofit a commercial fundus camera with a polarization-based optical system to photograph the retina. The polarization optics include a pair of Savart plates which encode the polarization state of light passing through the plates. Images captured with the device contain both the retinal image, as well as a fringe pattern superimposed on top of the image. Distortions in the fringe pattern change depending upon the degree of linear and circular polarization introduced by the retinal nerve fibers. Fourier analysis is used to analyze the captured image and extract the Stokes vectors from the image.
To date, we have fabricated the Savart plate system and have photographed both static polarization elements such as a linear retarder and a circular polarizing filter, as well as a biological sample. We have been able to reliably retreive the different Stokes parameters within an accuracy of 5% except for in regions of high spatial frequency content and specular reflection.
The Savart system shows promise for measuring nerve fiber layer thickness in vivo. Current problems with high spatial frequency error and specular reflection are expected to be minimal for the eye due to the smooth intensity variations and diffuse nature of the retina.
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