title: Measuring the precise area of peripheral retinal non-perfusion using ultra-widefield imaging and its correlation with the ischaemic index.
abstract: 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 mm(2), 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 mm(2) to 365.4 mm(2) (mean 95.1 mm(2)), while the mean total visible retinal area was 697.0 mm(2). 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 (mm(2)). Eyes with RVO show large areas of peripheral retinal non-perfusion.
authors.affiliation: National Healthcare Group Eye Institute, Tan Tock Seng Hospital, Singapore, Singapore Fundus Image Reading Center, National Healthcare Group Eye Institute, Singapore, Singapore.
authors.forename: Colin S
authors.initials: CS
authors.lastname: Tan
authors.affiliation: National Healthcare Group Eye Institute, Tan Tock Seng Hospital, Singapore, Singapore.
authors.forename: Milton C
authors.initials: MC
authors.lastname: Chew
authors.affiliation: Global R&D, Optos Plc, Dunfermline, UK.
authors.forename: Jano
authors.initials: J
authors.lastname: van Hemert
authors.affiliation: Department of Ophthalmology, Medical Center Ophthalmology Associates, San Antonio, Texas, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Singer
authors.affiliation: Department of Ophthalmology, Medical Center Ophthalmology Associates, San Antonio, Texas, USA.
authors.forename: Darren
authors.initials: D
authors.lastname: Bell
authors.affiliation: Doheny Eye Institute, University of California Los Angeles, Los Angeles, USA.
authors.forename: SriniVas R
authors.initials: SR
authors.lastname: Sadda
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002196:Capillaries / Q000473:pathology; D005260:Female; D005451:Fluorescein Angiography; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007511:Ischemia / Q000145:classification / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012170:Retinal Vein Occlusion / Q000145:classification / Q000175:diagnosis*; D012171:Retinal Vessels / Q000473:pathology*
keywords: Imaging; Retina