With ultra-widefield angiography, we have ascertained that posterior pole nonperfusion of more than 10 DA remains the key risk factor for new vessel development compared to areas of nonperfusion confined to the periphery.

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2 Structured Abstract Purpose:To validate the use of concentric rings as a method to measure topographical area of retinal non-perfusion in ultra wide-field angiography with the ischemic index method, which is the most frequently used method to measure non-perfusion in ultra widefield angiography. Design:Validation study and reliability analysis Methods:Setting: Single centre study performed at National Institute for Health Research Moorfields Biomedical Research Centre, London, United Kingdom.Study Population: 28 ultra wide-field angiogram images of eyes with central retinal vein occlusion.Observation Procedure: The concentric rings method consist of six macula centered concentric rings divided into 12 segments each. Each image was graded by five graders using both the concentric rings and the ischemic index methods. Main Outcome Measures:Agreement between the two methods was calculated using the intraclass correlation coefficient. Intertest agreement, intergrader agreement, test-retest reliability and the time taken to grade using these two methods were compared. Results:The intertest agreement between concentric rings method and ischemic index method was 0.965. The intergrader agreement was 0.910 for concentric rings method and 0.898 with the ischemic index method. The test-retest reliability was 0.975 for the rings and 0.979 for the ischemic index. Average grading time per image was 187s and 297s for concentric rings method and ischemic index method respectively, p=<0.001. Conclusion:The concentric rings method has an 'almost perfect' intergrader agreement and intertest agreement with the ischemic index method with a shorter grading time. Text IntroductionFundus fluorescein angiography (FA) remains the gold standard imaging tool for the measurement of retinal perfusion status in retinal vascular diseases. Previous seminal research papers such as the Early Treatment Diabetic Retinopathy Study 1 and the Central Vein Occlusion Study 2 classified retinal perfusion status based on the montage of overlapping 7-field FA images. However, 7-field imaging only allows visualisation of approximately a third of the retinal surface area. The acquisition of these 7-field images are also technically challenging and require well-trained photographers, well-dilated pupils and good patient co-operation to undergo multiple flash photography. Furthermore, a single 7-field montage image is formed of images acquired at different FA phases. These limitations have been overcome by the introduction of ultra wide-field imaging. The ultra wide-field imaging has a shorter image capture time and allows visualisation of significantly larger areas of the retina using less number of images compared to the conventional 7-field imaging. For example, the ultra wide-field image obtained by Optos Plc, Dumfermline, Scotland, United Kingdom covers approximately a 200 degree field of view in a single image compared to the 30 to 50 degree conventional fundus cameras and is now regularly used in clinical practice 3-9 .The conventional measurement of...