Scanning Laser Ophthalmoscope

A scanning laser ophthalmoscope is an instrument that uses a collimated beam of laser light to image the ocular structures, especially the retina and optic nerve head. The SLO achieved a drastic reduction in the amount of light required to image the posterior segment of the eye in contrast to indirect ophthalmoscope and conventional fundus camera, thereby improving patient comfort during the procedure. The "flying tv ophthalmoscope" was the very first SLO introduced in 1980 by Robert. H. Webb. The incident highly radiant laser beam uses only the central 1 mm of the pupillary aperture, and the scattered light is collected back from the remaining pupillary aperture. This arrangement was termed "co-pupillary."  Though SLO for clinical practice was introduced as early as 1990, it was not routinely utilized due to disadvantages like inferior resolution, bulky equipment, and cost. These disadvantages were overcome by a "confocal" arrangement where the scattered light rays from the ocular structures are detected at a focal point conjugate to the focus of the point illuminated. The recent scanning laser ophthalmoscopes are equipped with high-powered laser beams, smaller confocal apertures, and extremely sensitive detectors, which has made them an invaluable tool in imaging the retina and the optic nerve in clinical practice. When combined with adaptive optics, it helps in the elimination of optical aberrations, thus making the visualization of individual photoreceptors possible in vivo.