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Francesco LaRocca, Al-Hafeez Dhalla, Sina Farsiu, Joseph A. Izatt; Optimization of a Compact CSLO Design. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3103.
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© ARVO (1962-2015); The Authors (2016-present)
Confocal Scanning Laser Ophthalmoscopy (CSLO) enables high resolution and high contrast imaging of the retina by employing spatial filtering for scattered light rejection. A compact CSLO design would enable more versatile applications including hand-held operation, however optical throughput scales with scanner aperture and thus overall system size in conventional CSLO designs. We describe a simple, compact optical CLSO design optimized to balance resolution and throughput while minimizing common imaging artifacts such as lens and corneal reflections.
The illumination optics in the compact CSLO design were optimized to create a near diffraction-limited spot size at the retina across a 15° field of view (FOV). The wide-field schematic eye model with gradient-index lens by Goncharov and Dainty was used to determine the spot size at the retina. Using non-sequential optical modeling, the collection optics were optimized for collection of light scattered from the retina simultaneous with rejection of corneal surface reflections. To optimize retinal scattered light collection, a study was performed of retinal image sharpness versus collection throughput for seven pinhole sizes between 0.5 - 4.5 TDL (times diffraction limited). This study employed a simple variation of the image focus measurement technique by Kautsky et al, which is the ratio of the L2 norm of the high-passed image and the L2 norm of the low-passed image. All remaining reflections from fixed lenses in the optical train were successfully removed using background subtraction.
The volume of the implemented CSLO design was 683 cm3, and can be reduced further by use of custom lenses and improved packaging of the mechanical scanners. Optimal image sharpness with acceptable throughput was obtained for a pinhole size of 0.7 TDL. Excellent retinal image quality was obtained up to 30° FOV with no corneal artifact for a wide range of patient alignment conditions. A sample 30° image acquired at 8 frames per second with 500 lines per frame and a pixel density of 1000 samples per line is shown in Fig.1.
We demonstrate a simple, compact CSLO optical design with near diffraction-limited performance simultaneous with elimination of common artifacts.
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