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Measuring the precise area of peripheral retinal non-perfusion using ultra-widefield imaging and its correlation with the ischaemic index
  1. Colin S Tan1,2,
  2. Milton C Chew1,
  3. Jano van Hemert3,
  4. Michael A Singer4,
  5. Darren Bell4,
  6. SriniVas R Sadda5
  1. 1National Healthcare Group Eye Institute, Tan Tock Seng Hospital, Singapore, Singapore
  2. 2Fundus Image Reading Center, National Healthcare Group Eye Institute, Singapore, Singapore
  3. 3Global R&D, Optos Plc, Dunfermline, UK
  4. 4Department of Ophthalmology, Medical Center Ophthalmology Associates, San Antonio, Texas, USA
  5. 5Doheny Eye Institute, University of California Los Angeles, Los Angeles, USA
  1. Correspondence to Dr SriniVas R Sadda, Doheny Eye Institute-DEI 3623, 1450 San Pablo Street, Los Angeles, CA 90033, USA; SSadda{at}


Objective To determine the calculated, anatomically correct, area of retinal non-perfusion and total area of visible retina on ultra-widefield fluorescein angiography (UWF FA) in retinal vein occlusion (RVO) and to compare the corrected measures of non-perfusion with the ischaemic index.

Methods Uncorrected UWF FA images from 32 patients with RVO were graded manually for capillary non-perfusion, which was calculated as a percentage of the total visible retina (uncorrected ischaemic index). The annotated images were converted using novel stereographic projection software to calculate precise areas of non-perfusion in mm2, which was compared as a percentage of the total area of visible retina (‘corrected non-perfusion percentage’) with the ischaemic index.

Results The precise areas of peripheral non-perfusion ranged from 0 mm2 to 365.4 mm2 (mean 95.1 mm2), while the mean total visible retinal area was 697.0 mm2. The mean corrected non-perfusion percentage was similar to the uncorrected ischaemic index (13.5% vs 14.8%, p=0.239). The corrected non-perfusion percentage correlated with uncorrected ischaemic index (R=0.978, p<0.001), but the difference in non-perfusion percentage between corrected and uncorrected metrics was as high as 14.8%.

Conclusions Using stereographic projection software, lesion areas on UWF images can be calculated in anatomically correct physical units (mm2). Eyes with RVO show large areas of peripheral retinal non-perfusion.

  • Retina
  • Imaging

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