PURPOSE: To determine equivalence of manual microaneurysm (MA) counts on UWF-CI and UWF-FA.
METHODS: Retrospective study of all patients at the Joslin Diabetes Center from 3/21/2012-12/21/2018 with type 1 or 2 diabetes and both UWF-FA and UWF-CI performed in the same eye within a 2-wk period. MAs were manually counted in individual ETDRS and extended UWF zones on both UWF-FA and UWF-CI. Fields with ≥ 20 MAs were used to assign DR severity per international classification system (0 fields=mild, 1-3=moderate, ≥4=severe). UWF-CI and UWF-FA MA count agreement and effect on DR severity were evaluated.
RESULTS: In 288 eyes (193 patients), UWF-CI DR severity was 2.4% no DR, 29.9% mild, 32.6% moderate, 22.9% severe NPDR and 12.2% PDR. UWF-FA MA counts were 3.5x higher than UWF-CI counts overall (414.4±375.2 vs 120.0±157.4,p<0.001), 3.2x higher in ETDRS fields (265.8±239.5 vs 81.8±100.1,p<0.001) and 5.3x higher in extended ETDRS fields (148.6±184.6 vs 28.2±74.8,p<0.001). In eyes with NPDR on UWF-CI (N=246), UWF-FA images had 2.3x more fields with ≥20 MAs than UWF-CI in the ETDRS fields and 2.0x more in all total fields (p<0.001), with only fair agreement between modalities (k=0.325,0.313). In ETDRS fields, agreement for DR severity based on MA counts increased from k=0.346 to 0.600 when dividing UWF-FA counts by a factor of 3 and declined rapidly in agreement thereafter. Total ultrawide field DR severity agreement increased from k=0.317 to 0.565 with an adjustment factor of 4-5. UWF-FA with MA counts ≥20 were compared to DR severity determined by formal ETDRS grading of UWF-CI. Within the ETDRS fields, kappa agreement increased from 0.543 uncorrected to 0.643 when adjusting by a factor of 2 followed by a rapid decline thereafter. Highest agreements with formal ETDRS grading were observed with total UWF-CI MA count (k=0.656), UWF-FA ETDRS counts at threshold=2 (k=0.643) and UWF-FA total field counts at threshold=4 (k=0.584).
CONCLUSIONS: UWF-FA detects 3.2-5.3x more MAs and 2.0-2.3x more fields with MAs≥20 than UWF-CI at all DR severity levels, thus limiting direct comparison between these modalities. Correcting UWF-FA MA counts can substantially improve agreement between UWF-FA and UWF-CI derived DR severity and should be considered when using UWF-FA MA counts to assess DR outcomes.
