Scanning Laser Ophthalmoscopy
The scanning laser ophthalmoscopy (SLO) is a retinal imaging modality that is similar to the standard scanning laser microscope. The major difference is that the optics of the eye function as the objective/condenser lens. As the system has a confocal aperture in front of the detector, the imaging performance is fundamentally better than in the traditional fundus imaging. Typically the SLO utilizes horizontal and vertical scanning mirrors to scan a specific region of the retina with a focused laser spot and create raster images. Besides acquiring normal reflectance images, SLO can be used for other retinal imaging modalities including fluorescein angiography, ICG angiography and fundus autofluorescence.
Optical diagnosis of Alzheimer’s disease
DMD for retinal imaging and motion detection
This research project is focusing on technical development of the scanning laser ophthalmoscopes to improve their performance capabilities. Instead of raster-scanning a focused laser spot over the area of interest in the retina, a digital micromirror device (DMD) is used for illumination. With the DMD, the retina is illuminated with multiple parallel lines simultaneously instead of raster-scanning a spot and these patterns are then shifted to create a scanning effect. After all the whole field of view is scanned, the retinal image is created in post-processing. As these patterns can be projected fast (100 Hz or faster), it makes the system suitable for detecting the horizontal and vertical eye translation from the acquired frames.
Multispectral imaging using DMD
Scanning Light Ophthalmoscope (SLO) has become an essential diagnostic tool in ophthalmology by allowing visualisation of retinal structures. Spatial modulators such as the Digital Micromirror Device (DMD) have proven to eliminate the scanning mirrors by projecting a series of scanning patterns. Multispectral imaging is an emerging modality for ophthalmic applications as simultaneous recording of spectral information at each spatial imaging point enables quantitative mapping of vital physiological parameters indicating retinal health condition. The majority of the Multispectral imagers are either based on a fundus camera with low resolution or they use expensive components such as supercontinuum source and detector arrays. Here, we present a compact DMD retinal imaging. The system is configured to simultaneously record and display the confocal reflectance image of the fundus at two wavelengths in high speed.
Simplified schematic of the imaging system
Imaging in the right eye of a healthy volunteer (A): Wide field image obtained without pinholes, (B): confocal image after applying virtual pinholes, (C): Confocal image of the optic nerve head at 810 nm (D) Confocal image of the optic nerve head at 770 nm (E) Confocal image of the fovea at 820 nm (F) Confocal image of the fovea at 770 nm.