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Mathi Damodaran, Kari Viljami Vienola, Boy Braaf, Koen Vermeer, Johannes F De Boer; Multispectral Scanning Light Ophthalmoscope (MSLO) using optimized illumination schemes. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1697. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
We present an MSLO capable of recording spectral information at each spatial imaging point to enable quantitative mapping of vital physiological parameters indicating retinal health condition.
The imaging system (Fig.1) uses a Digital Micromirror Device (DMD) to create parallel illumination on the retina. An annulus is placed conjugate to the pupil to create annular illumination at the pupil of the eye. This allows imaging the retina through the central un-illuminated portion of the pupil and effectively reduces corneal back reflections. A healthy retina was imaged at 150 Hz with a fill factor 1/20 (i.e.,20 patterns required to create a full field image) resulting in a full-field image frame rate of 7.5 Hz. The reflected light from the retina is collected using a CMOS camera. By adding the images for each pattern, we get a wide field image (Fig.2A) and upon background subraction by post-processing, we get the confocal image (Fig.2B). We imaged the right eye of a healthy male subject at 820 nm and 740 nm wavelengths.
Fig.2B suffers from corneal haze and out-of-focus signals which is removed in Fig.2C to reveal the optic nerve head and the blood vessels. Fig. 2C and 2D shows the multispectral images of the same region at 820 nm and 740 nm respectively, clearly showing the different reflectivity of the structures at different wavelengths. Fig.2D and 2E shows the macular region with small blood vessels visible at the same wavelengths.
We have demonstrated multispectral retinal imaging of human fundus using a DMD and a CMOS camera combined with different LED illuminations. The modular design of the system allows imaging using different wavelengths easily at a low cost. By combining the advantages offered by the DMD technology and multispectral imaging, we aim to make the imaging system suitable for diagnosis and screening of eye diseases.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Fig.1 MSLO: Light from the LED is homogenized using a light pipe, which uniformly illuminates the DMD. DMD is programmed with scan pattern which is then projected on the retina using relay optics. The annulus (A) is placed in the pupil plane (Aperture 1).
Fig.2 Imaging in the right eye of a healthy volunteer (A): Wide field image and (B): confocal image. Multispectral Imaging of Optic nerve head (C:820nm, D:740nm) and macula (E:820nm, F:740nm). Scale bar corresponds to 2o in the retina.
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