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L. D. Hubbard, W. Sun, P. A. Cleary, D. P. Hainsworth, Q. Peng, R. A. Susman, R. P. Danis, Diabetes Control & Complications Trial/Epidemiology of Diabetes Interventions & Complications Study; Comparability of Digital vs. Film Grading of Diabetic Retinopathy Severity in DCCT/EDIC. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4674.
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To compare diabetic retinopathy (DR) severity levels when switching from film (F) to digital (D) retinal images in a long-term multi-center study.Introduction: Long-term studies require consistent measurements across clinics and over time for valid conclusions. During the past 25 years, the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study (DCCT/EDIC) have used 7-field stereo color film photos, per ETDRS protocol. Obsolescence of film photography has now forced EDIC to transition to digital imaging. Thus, EDIC conducted an ancillary study of the potential impact of this transition.
At 20 clinics during 2007-2009, 310 type-1 diabetic participants, spanning the ETDRS scale, were imaged with both F and D cameras. Central grading independently assessed DR severity levels from F and D (tonally standardized at Reading Center). For retinopathy outcomes with >10% prevalence, we had ≥85% power to detect an agreement kappa (K) of 0.7 to 0.9.
Comparing DR severity gradings, D vs. F yielded weighted K of 0.74 for eye level and 0.73 for patient level. Digital grading did not systematically under- or overestimate levels (McNemar overall bias test, P=0.14). Regarding major DR outcomes (e.g., 3-step progression, mild/moderate/severe NPDR/PDR or worse), D vs.F kappas were 0.7 to 0.96 ("substantial" to "perfect"). Agreement proportion was 86% - 99%, sensitivity 75% - 98%, and specificity 72% - 99%. Major study conclusions were similar with D vs. F gradings (e.g., adjusted odds reductions with intensive DM therapy for PDR at EDIC year 10: 65.5% [D] vs. 64.3% [F]). Finally, Kappas for major DR outcomes were comparable across all clinics (Cochran’s homogeneity test, all P>0.2).
This is the first multi-center, long-term study comparing DR severity with D vs. F. We show that ETDRS scores from D and F are similar, and that the high reliability of DR evaluations seen historically in DCCT/EDIC will continue with digital photography.
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