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Gang Luo, Zhengzhou Li, Eli Peli; Mobile Electronic Magnification Device For People With Central Vision Loss. Invest. Ophthalmol. Vis. Sci. 2011;52(14):386.
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A head mounted display (HMD) device implementing an on-demand magnification concept for mobile use by people with central vision loss was proposed. A pilot experiment was conducted with patients to evaluate a prototype in visual function testing and a search-and-walk experiment.
We developed a magnification device based on an optical see-through HMD attached with a miniature video camera, which provides adjustable magnification from 2 to 16×. When safe mobility is needed, a seeing-through natural view is enabled. When patients need to see details, they can turn on LCD shutters to block the see-through view, which provides dark background for magnified and contrast-enhanced scene images in the display. Distance visual acuity (VA) and contrast sensitivity (CS) were tested, and performance on a search-and-walk-to-target task was measured in a large (17’ by 27’) empty room, where 10 similar pictures of human faces were posted on the walls. From a fixed start point, subjects had to identify and walk to a given target. If the target they walked to was incorrect, they returned to start point and repeated attempts until the correct target was found. Two subjects (one with retinopathy of prematurity and another with cone dystrophy) have been tested.
Visual function was substantially improved with the device for both subjects (VA: 1 to 0.04 and 1 to 0.24 logMAR, CS: 1.5 to 1.95, and 0.65 to 1.25 log, respectively). In the search-and-walk task, the device reduced the number of attempt (4.3 to 1 and 4.3 to 2.7, respectively), and search time was reduced for one subject (51 to 33 sec.), but not the other (72 to 104 sec.), who reported the testing time was much longer than he can spend on his computer and it caused great eye strain.
When using the device, the magnification improved patients’ VA. Our image enhancement method also improved CS, which has not been achieved by other similar devices (Culham, OPO 2004). The on-demand magnification device may help patients see distant objects while not restricting their mobility. It has the potential to be useful in tasks that require mobility.
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