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M. S. Muller, A. E. Elsner, D. A. VanNasdale, B. P. Haggerty, T. D. Peabody, R. C. Gustus, B. L. Petrig; Low Cost Retinal Imaging for Diabetic Retinopathy Screening. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3305.
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To provide low-cost, nonmydriatic screening for diabetic retinopathy (DR) with our novel retinal imaging system, the laser scanning digital camera (LSDC). To provide a level of contrast of retinal vessels that is sufficient to monitor pathological changes and to provide a high sensitivity of referral.
Our LSDC prototype is a confocal slit-scanning ophthalmoscope that uses a small pupil entrance / exit diameter of 2.5 mm to perform nonmydriatic, near infrared retinal imaging at 5.6 frames per second. A wide 36° imaging field of view and a working distance of 28 mm has been achieved. A single focusing knob permits easy adjustment over a wide range of visual acuity (+6 to -8 diopters). Pupil alignment is assisted in real-time with a second anterior segment camera, which also allows determination of pupil size and iris pigmentation in post-processing.An initial feasibility study of 61 participants aged 24 to 79 has been performed. This group includes 18 patients with mild to moderate DR and age-, gender- and race-matched controls. LSDC image quality was assessed by calculating the Michelson contrast over a major retinal artery or vein 2.5 optic disc diameters from the center of the optic nerve head. For each participant, a series of twenty images were acquired at different confocal aperture sizes for both fovea- and optic nerve head-centered views. The mean and standard deviation of the Michelson contrast were calculated from up to ten images per patient for the optic nerve head-centered datasets.
Images with a Michelson contrast of retinal vessels >0.15 are typical in our sample. There is no systematic loss of image quality observed between diabetic patients, their respective matched control subjects, or participants with darkly pigmented eyes. A repeatability study in 5 normal subjects, tested weekly over 4 weeks, resulted in an average coefficient of variation of <10% at each aperture size.
Initial feasibility results have shown excellent potential for the LSDC to be used as a low-cost screening device for diabetic retinopathy.
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