Age-related macular degeneration (AMD) is the most common cause of irreversible central vision loss and legal blindness in developed countries.1–3 AMD represents a chronic disease with various phenotypic manifestations, disease stages, and rates of progression over time. Severe vision loss results from choroidal neovascularization (CNV), pigment epithelial detachment, or geographic atrophy (GA) of the retinal pigment epithelium (RPE).4 While CNV is the most common cause of vision loss, GA is responsible for approximately 20 % of severe visual impairment in AMD.5–8 The chronic nature of the disease, limited treatment options, and the aging population are all factors suggesting that the prevalence of AMD will increase with time unless effective interventions are developed. Retinal imaging plays a critical role in the detection and management of disease because it can reveal lesions difficult to visualize by funduscopic examination. Color fundus photography is the standard imaging modality used for assessment and documentation of AMD. Fluorescein angiography provides additional functional information on vascular involvement, which is important in the detection of CNV and other complications of advanced disease that involve disturbance of the blood–retinal barrier. The scanning laser ophthalmoscope (SLO) adds the ability to test and image the retina in a point-by-point fashion, which enhances the evaluation of structural and functional changes in the disease process of exudative and non-exudative AMD.
The SLO was originally developed by Pomeranzeff and Webb to provide high-contrast images of the retina at illumination levels 1/1,000 of those required for indirect ophthalmoscopy.9 The SLO scans a low energy laser beam (or other coherent illumination source such as the superluminescent diode) across the fundus and reconstructs images from reflected light, creating images with a higher level of contrast compared with fundus photography.10,11 The technology of the sweeping illumination source provides a platform from which additional testing such as fluorescein angiography, manual and automated perimetry, and reflectometry of cone pigment densities can be accomplished.10,12–15
Additional modifications of the device lead to the confocal SLO (cSLO), which uses light from a single plane for image reconstruction. By rejecting the returning scattered light, the cSLO provides improved contrast and complete retinal images (40°) without dilation of the pupil.11,16
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