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C. A. Clark, M. S. Muller, A. E. Elsner, B. L. Petrig; Refractive Error Across the Posterior Pole Using a Novel Retinal Imaging Technique. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1007.
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To provide low-cost, nonmydriatic screening for refractive errors and refractive error changes such as those encountered in macular. To use a novel retinal imaging system, the laser scanning digital camera (LSDC), to provide refractive error maps across the visual field.
Six subjects with refractive errors ranging from +4.00 to -4.75 were studied. An LSDC prototype illuminated the retina with structured illumination (850 nm) to increase contrast in the retinal images, provided by modulating the light source in a striped pattern. The Michelson contrast at each location on the retina was measured while stepping through focus. Retinal images were captured using a 1 megapixel sensor array. For each subject and a model eye, through focus retinal images of 36 deg were acquired, using 0.25 or 0.50 diopter steps to compare resolution. The range of the focusing stage allows for detection of refractive errors from +10 to -14 diopters both for central refractive error and across a retinal field of 36 degrees. Subjects viewed a 20/60 letter target at distance during measurement. A spline function was used to interpolate the peak contrast across the through focus image series. Bland-Altman analysis was used to compare the subjective refraction with the LSDC auto-refraction.
The through focus data showed that it was feasible to measure refractive error using the LSDC with structured illumination technique, demonstrating landmarks such as the foveal pit, foveal crest, and optic nerve head. There was no statistical difference between 0.25 and 0.50 steps for measuring central refraction. However, 0.25 diopter steps improved the quality over the 36 deg field of the refractive topographical map compared with the 0.50 steps.
Initial feasibility results have shown the potential for the LSDC to be used as a low-cost device for both retinal imaging and refractive error measurement. The refractive topographical maps provide the potential to screen for changes in retinal topography such as macular edema.
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