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Danielle J. Harper, Marco Augustin, Antonia Lichtenegger, Pablo Eugui, Martin Glösmann, Christoph K Hitzenberger, Bernhard Baumann; White Light Optical Coherence Tomography for Sub-Micron Resolution and Spectroscopic Imaging in the Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5826.
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To obtain sub-micron axial resolution in vivo images of both the healthy and the diseased murine retina using white light optical coherence tomography (OCT) and to perform a spectral analysis based on the acquired images.
A white light spectral domain OCT system was developed using a supercontinuum laser as a light source. By detecting backscattered light across the whole visible light range (400 – 700 nm), the system has a measured axial resolution in air of 1.0 µm, corresponding to 0.73 µm in retinal tissue. An A-scan rate of 25 kHz allowed for 3D imaging of the murine retina in approximately eight seconds. The mice were anesthetized using isoflurane and pupils were dilated using tropicamide and phenylephrine. Artificial tear drops were also applied to keep the eyes moist. The OCT system was used to image both the healthy murine retina and the very-low-density-lipoprotein-receptor (VLDLR) knock-out mouse model which is known to develop pathologic retinal features, such as neovascularization, anastomoses and retinal degeneration. A spectroscopic analysis was then performed on the images by filtering the acquired spectra using three Gaussian windows centered at different wavelengths and adding these three channels together to form an RGB image.
Sub-micron axial resolution was achieved in vivo in the murine retina, allowing a clear identification of the retinal layers. As the external limiting membrane (ELM) is the boundary between the inner segments of the photoreceptors and their cell nuclei, its apparent thickness (0.91 – 0.97 µm) corresponds to the measured axial resolution of the OCT system in the eye. The images of the VLDLR-/- mouse model show retinal lesions disrupting the retinal pigment epithelium (RPE) and the surrounding layers. White light OCT also allows a 3D spectroscopic analysis to be performed without any additional measurements, showing different color contrasts for different tissues in the inner retinal layers. Only the red light penetrates to the choroid. The colors observed in the spectroscopic en-face image are similar to those seen in murine fundus photography.
The use of white light for OCT results in high resolution images and also in an opportunity to visualize the response of retinal tissues to illumination by different wavelengths. This could be promising for a more detailed analysis of retinal disease progression.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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