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Graham Strong; New video-based assistive technologies for low vision. Journal of Vision 2004;4(11):5. doi: 10.1167/4.11.5.
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Over the past decade, electro-optical technology has evolved as an important platform for the development of contemporary assistive devices for people with low vision. Video-based devices are now commercially available in iterations corresponding to all commonly differentiated categories of optical low vision aids — hand held, stand mounted, face worn, and head borne magnifiers and telemicroscopes. With several notable exceptions, these developments are manifestations of “technology push” initiatives aimed at replicating the established functionality of conventional CCTV systems within smaller, more portable embodiments by utilizing recent innovations in sensor, display, and lighting technologies. Most of these compact video magnifiers incorporate a variable, but modest, range of magnifications combined with several contrast enhancement selections. Their major weaknesses include over-magnification, mediocre colour rendering, reduced display contrast, narrow viewing angles, aspect ration distortions, non-intuitive camera/display juxtapositions, and modestly limited fields of view. Nonetheless, these devices have been well-received by many low visioned users because they offer several unique advantages over optical magnifiers for some applications. Video devices with distance viewing capabilities are somewhat more ubiquitous. Clinical experience with these multifaceted systems provides greater insight into the full potential of video technology for low vision applications. Their theoretical potential derives from the fundamental posits of contemporary clinical analysis. “Low vision” commonly describes any untreatable condition of diminished vision that interferes with an individual's ability to perform common visual tasks such as reading. Underpinning these functional seeing disabilities is a unique assortment of measurable deficits in tested visual function. These elemental impairments often include visual acuity reductions, contrast sensitivity deficits, glare sensitivity, visual field defects, diminished scotopic or photopic function, and photo-recovery deficiencies. Optical devices invariably produce fixed levels of magnification that provide effective solutions for people with relatively specific impairments performing fairly specific seeing tasks. This approach is somewhat one-dimensional since it invokes a visual acuity solution for all impairment presentations. Video-based technology allows developers to incorporate a much broader range of enhancement options in a single low vision device. These devices produce a video-mediated reality that can be selectively tuned to redress the multifaceted visual deficiencies of most users with respect to most seeing tasks. Our experience with video telescope users reveals the utility of several novel viewing strategies that are exclusive to video device use, including innovative orientation and localization strategies that are potentiated by their zoomable user interface. Another significant performance feature of video devices is their intrinsic capacity to create readily discernable images within a wide range of hostile viewing environments. The increased availability of new video-based low vision devices poses a significant challenge for contemporary vision rehabilitation service providers, who must now resolve their integration into well-established low vision assessment protocols. The growing range and versatility of video devices establishes a viable alternative for most optical sight enhancement systems that is best evaluated using organized assessment protocols that allow assessors and users to directly compare the two intervention options.
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