Abstract
Purpose: :
To compare diabetic retinopathy (DR) severity levels graded from enhanced stereo color digital retinal images to those graded from slide film photographs.
Methods: :
Film (F) and digital (D) color images of 154 eyes of persons with diabetes (pre-selected for full range of DR) were taken with a Topcon 35o camera as 7 stereo fields [7SF] per DRS/ETDRS protocol. Three graders independently determined Early Treatment Diabetic Retinopathy Study(ETDRS) DR level from F (slide transparencies on light boxes with Donaldson viewers) and D (2392 x 2048 pixel, uncompressed images viewed on calibrated 20" LCD monitors with hand-held stereo viewers in Topcon IMAGEnet). Digital images were standardized for brightness, contrast and color balance according to the AREDS2 image model, yielding film-like consistency. In D, the green channel (similar to red-free) was also examined. DR levels were defined by central tendency among graders. Custom software controlled order/timing of grading to minimize bias and recall.
Results: :
Graders classified DR from F images as follows: no DR = 26 eyes, non-proliferative DR (NPDR) - 97 eyes (microaneurysms only, mild/moderate/severe = 8/35/25/29), proliferative DR (PDR) = 30 eyes (mild/moderate/severe = 10/10/10), and ungradable DR = 1 eye. Comparison of D vs. F classifications for specific ETDRS level (9-step scale) yielded 66.9% exact agreement and 94.8% +1 step (unweighted Κ = 0.62, SEΚ = 0.04; linear weighted Κ = 0.83, SEΚ = 0.03). For historical comparison, agreement in ETDRS from single replicate gradings of F using the same scale (ETDRS report #12, Ophthalmology 1991) was lower: 53% exact and 88% +1 step (unweighted Κ = 0.42). In our study, variability observed between media was similar to that observed between graders within each medium.
Conclusions: :
Comparing D 7SF with F 7SF after standardized enhancement of D, our DR evaluations from D were similar to those from F. Unlike some previous reports using unenhanced digital images which showed lower sensitivity of D for levels defined by subtle abnormalities (microaneurysms, IRMA, new vessels), we found no evidence of systematic disadvantage for D compared to F over a broad range of DR severity.
Keywords: diabetic retinopathy • clinical (human) or epidemiologic studies: outcomes/complications • imaging/image analysis: clinical