Abstract
Abstract: :
Purpose: We describe a method of transforming slit–lamp video into wide–field retinal imagery using a prototype system. Slit–lamp bio–microscopes are commonly used for direct viewing retinal conditions. Less expensive and more widely available than fundus cameras, slit–lamps generally produce retinal imagery inferior to fundus cameras due to small fields of view and specular reflections. Methods: Slit–lamp video images were acquired through a handheld lens and analog video camera attached to a slit–lamp bio–microscope. Video images were digitized and wide–field mosaic retinal images generated using automatic specularity removal, hierarchical robust image registration, mosaic construction, mosaic blending, intensity and color equalization. Results: Average mosaic image field sizes were 17° superiorly, 35° temporally, 18° inferiorly and 24° nasally. Slit–lamp mosaic fundus images from ten normal eyes were qualitatively compared to digitized 35mm fundus images of similar areas of the central retina. Bright, white specular reflections were automatically eliminated from slit–lamp images. Residue reflections were transferred from videotape to mosaic images. Faint, purple oval reflections were deemed non–obstructive to the retina view. Other multiple reflections were small and white, which could be mistaken as retinal pathology. Choroidal details, temporal optic disc margin and cup–to–disc ratios were less consistently discernable on slit–lamp mosaic images than 35mm film. Conclusions:To the best of our knowledge, these are the widest field–of–view retinal images yet created through slit–lamp photography. Mosaic slit–lamp images expanded the retina view, enabling single–field observation of the optic disc, macular and central retina. Slit–lamp is a basic, primary diagnostic tool available in almost every eye care provider office. Transformation of slit–lamp into wide–field retinal imagery provides the ground work for a wide range of future applications including telemedicine.
Keywords: image processing • imaging/image analysis: clinical • retina