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A Sharma, M Barakat, B Madjarov; Accurate Determination of the Ischemic Retinal Areas in Branch Retinal Vein Occlusion . Invest. Ophthalmol. Vis. Sci. 2002;43(13):493.
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Purpose: The dimensions of the areas with capillary non-perfusion in patients with branch retinal vein occlusion (BVO) correlate well with the risk for development of retinal neovascularization. In clinical practice the ischemic areas are roughly estimated or measured inadequately using a greater linear dimension. The measurement task becomes more challenging when such areas extend beyond a single photographic field. Our goal is to develop and validate more accurate methods for area calculation in patients with BVO. Methods: 21 eyes (21 patients) were selected from the clinical archives. Only patients with foveal involvement and extensive areas of capillary non-perfusion evident from the fluorescein angiograms were included in the study. Film-based fluorescein angiograms were digitized at 1000 dpi (Nikon Super CoolScan 4000 ED), 24 bits per pixel to an image size of 1100x945. An algorithm was developed and implemented to permit digital composition from two adjacent overlapping photographic fields. Incorporated graphical capabilities in the custom developed software allowed for precise outlining of a single or multiple ischemic segments on the composed digital image. Measurements were displayed in square pixels or standard disc areas for each single area. The total area was also calculated as a sum of non-adjacent areas. Results: The graphical user interface of the software allowed for a facile interactive construction of digital wide field images. The outlining capability demonstrated a robust performance on single and composed digital images. The results for the total area dimensions ranged from 8434.4-44824.89 square pixels, 0.385-2.049 disk areas. The mean for the eyes, which were not at risk for development of neovascularization by the current standards was 18644.38, 0.850 and standard deviation was equal to 12967, 0.592 in square pixels and disk areas, respectively. Conclusion: Computer algorithms allow for precise delineation and accurate measurement of large non-perfused retinal areas. Further correlation between the established clinical standards and exact area dimensions may improve the management of BVO.
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