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H. Song, X. Qi, T. Y. Chui, Z. Zhong, W. Zou, S. A. Burns; High Speed Electro-optics Based Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO) Polarimeter. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1055.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate light tissue interactions in the retina using high magnification adaptive optics and near infrared imaging. While most light returning from the retina retains polarization, light which has been multiply scattered can be depolarized. We developed a technique to measure the Stokes Vector of light returning from the retina by using dual electro-optical crystals (LiNbO3) in a modified adaptive optics scanning laser ophthalmoscope (AOSLO).
We used the Indiana AOSLO to image the retina in near infrared light (15 nm bandwidth centered at 830 nm). The illuminating light was elliptically polarized, and a polarization analyzer was placed at the detection channel. The analyzer consists of two electro-optical crystals (orientated at 0 degree and 45 degree), followed by a linear grid polarizer at 0 degree and an avalanche photodiode detector. The imaging beam was steered by an 8 kHz horizontal scanner and a 15 Hz vertical scanner to sweep across the imaging region. Images of the retina of a field size of 1.8 x 0.2 deg were digitized at 640 x 512 pixels. The vertical scan was programmed to move vertically every 7 lines, during the 7 lines repeat scanning lines, the voltage to the electro-optics crystals was varied (from -180V to +180V in 60V step at 8 KHz). As a result, the birefringence of the two LiNbO3 crystals is modulated, allowing measurement of the Stokes Vector of the light returning from the retina for each line, with a complete measurement of 512 pixels occurring in less than 1 msec. The system has been tested both on artificial targets and a human eye.
Specular reflections from glass bead targets were polarization preserving as expected. In the human images, cones were readily imaged in the perifoveal regions. As expected, the image intensity for different features depended on the relation between input polarization and the birefringence of the two EO crystals.
We have developed and tested a superfast high resolution AOSLO for Stokes vector measurements of light returning from the retina. For each pixel in the image, the different polarization analysis conditions occur in approximately 1 msec, removing the artifact of the eye movements. Forming images based on different polarization properties allows us to measure the physical properties of eye tissue at the microscopic level.
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