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Y. Zhao, A. E. Elsner, B. P. Haggerty, D. A. VanNasdale, B. L. Petrig; Confocal Laser Scanning Digital Camera for Retinal Imaging. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4265.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a Laser Scanning Digital Camera (LSDC), an inexpensive, comfortable for patients and easy-to-handle device capable of non-mydriatic retinal imaging for a 40 deg field of view. To quantify the contrast of retinal vessel images captured by the LSDC and to study the contrast enhancement effect of different confocal aperture sizes.
We employed an 850 nm VCSEL laser, a cylindrical lens, and a rotating polygon mirror to create a narrow bright slit, which scans across a 40 deg retinal field in an undilated human eye. The photons returned from the retina are collected and coupled onto a MegaPixel CMOS detector array for image acquisition. A narrow linear aperture, reducing light not originating from the illuminated slit area on the retina, was used in the LSDC system to suppress the unwanted photons. Four different confocal aperture widths, equivalent to about 200, 400, 800, and 1600 microns on human retina, were used while taking LSDC images.
Retinal images of four undilated subjects were digitized with the four confocal apertures. For each image, profiles of arteries and veins were analyzed for the cross-sections about 10 deg away from the center of optic disk, and the Michelson contrasts were computed. For example, Fig. 1 shows an unprocessed LSDC image (200 micron confocal aperture) of a 33 year old Asian male (OD). A superior temporal artery and vein pair of this subject was analyzed for the image series taken with different apertures. The calculated contrasts are 0.209, 0.172, 0.113, 0.111 for the 120 micron wide vein, and 0.111, 0.093, 0.085, 0.071 for the 80 micron wide artery, for the smallest to largest aperture, respectively. These results show that the image contrast of retinal blood vessels strongly depends on the size of the confocal aperture.
The LSDC provided good contrast of retinal vessels across 40 deg field with nearly invisible near infrared light. The contrast was markedly enhanced by the use of a narrow confocal aperture. The application of the LSDC in telemedicine could improve the connection between underserved patients and eyecare providers.
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