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Srinivas R Sadda, Colin S Tan, Jano van Hemert, Darren J Bell, Milton Chew, Michael Singer; Correlation of precise area of peripheral non-perfusion with the ischemic index in retinal vein occlusion. Invest. Ophthalmol. Vis. Sci. 2014;55(13):247.
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As a result of non-linear distortion at the periphery of ultra-widefield (UWF) images, the extent of peripheral retinal non-perfusion (PRNP) has been quantified as a percentage of the total visible retina (ischemic index). Recent software advances now permit anatomically correct areas of PRNP to be calculated in mm2. In this study we compare the new corrected measures of PRNP with the ischemic index.
32 patients with branch or central retinal vein occlusion were recruited for standardized UWF (up to 200 degrees) fluorescein angiography (FA) using an Optos 200Tx. Uncorrected raw images were exported from the device and sent to the Doheny Image Reading Center (DIRC) for analysis by a masked, certified reading center grader. Using validated planimetric reading center grading software, the grader manually outlined all areas of PRNP as well as the total area of visible retina in order to calculate an ischemic index (percentage of visible retina that was non-perfused). The manually annotated images were converted using a “stereographic projection” method and accurate areas (in mm2) of perfused and non-perfused retina (in the visible field) were calculated. Both the corrected area of PRNP and the corrected non-perfusion percentage were compared with previously generated ischemic index.
Of the 32 eyes, the precise areas of PRNP ranged from 0 mm2 to 365.4 mm2 with a mean of 95.1 mm2. The corrected non-perfusion percentage ranged from 0% to 52.9%, with a mean of 13.5%. The uncorrected ischemic index ranged from 0% to 67.7%, with a mean of 14.8%. Both the corrected area of non-perfusion and the corrected percent non-perfusion correlated with the uncorrected ischemic index (R=0.978, p<0.001), but the max difference was 14.8%. A higher percentage of PRNP was associated with the presence of persistent edema (P<0.001). Following anti-vascular endothelial growth factor (VEGF) treatment, the area of PRNP was noted to decrease in 68.8% of cases, with a mean area of reversible PRNP of 16.3 mm2 and a max of 145.6 mm2.
Peripheral distortion on UWF images can be corrected, allowing calculation of lesion areas in correct physical units (i.e. mm2). Eyes with RVO can show large areas of PRNP which positively correlate with the severity of macular edema. A portion of the PRNP appears to be reversible with anti-VEGF therapy.
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