Demographics of patients (Table 1)
The medical records of 177 eyes of 90 DM patients were reviewed; 5 patients had type 1 DM and 85 patients had type 2 DM. In the DM group, 94 eyes of 51 patients (53.1%) had PDR, 53 eyes of 32 patients (29.9%) had moderate/severe NPDR, and 30 eyes of 16 patients (16.9%) had less than mild NPDR. Nine patients had signs of a different stage in one eye from that of the other one. Ninety-eight of the 177 eyes (55.4%) had received panretinal retinal photocoagulation (PRP) or local photocoagulation; 63 eyes with PDR, 35 eyes with moderate/severe NPDR, and none with less than mild NPDR. Fifty-three of the 177 eyes (29.9%) had received anti-VEGF therapies, and 33 of the 94 PDR eyes (35.1%) had undergone pars plana vitrectomy.
For the non-DM controls, 99 eyes of 50 patients who had widefield SLO examinations during the same period were analyzed. The control eyes included 7 eyes of 6 patients with RVO, 47 eyes of 34 patients with other retinal disorders, and 45 eyes of 36 patients without any retinal disorders. All 7 eyes with RVO had a branch retinal vein occlusion (BRVO). Other fundus diseases included 7 eyes with an epiretinal membrane, 7 eyes with Vogt-Koyanagi-Harada disease, 4 eyes with a rhegmatogenous retinal detachment, 4 eyes with multifocal posterior pigment epitheliopathy, 3 eyes with glaucoma, 3 with a macular hole, 3 with a peripheral vasoproliferative tumor, 2 eyes with dry AMD, 2 eyes with sarcoidosis, and 2 eyes with panuveitis. There were 45 eyes without any fundus disorders including the unaffected fellow eyes of patients with unilateral fundus disorders (23 eyes), dry eye (7 eyes), anterior uveitis (5 eyes), and cataract (3 eyes). Widefield SLO images were taken as one of the routine ocular examinations in these patients without fundus disorders.
Comparisons of the demographics of the DM group and controls are shown in Table 1. The differences in the mean age (63.0 ± 12.3 years in DM and 62.9 ± 14.8 in controls) and the mean refractive error (-1.6 ± 2.6 D in DM and − 3.2 ± 4.6 D in controls) were not significant. The DM patients had significantly poorer decimal BCVA than controls (0.29 ± 0.40 vs. 0.08 ± 0.26). There were significantly more men in the DM group than in the control group.
We also compared the demographics of the PDR, moderate/severe NPDR, less than mild NPDR, RVO, other fundus diseases, and no fundus diseases groups. The results showed that there were significant differences in the sex distribution, age, and BCVA (P < 0.001 in Chi-square test; P < 0.05 and P < 0.001 in Kruskal-Wallis test). There was no significant difference in the refractive error among the 6 groups (Kruskal-Wallis tests; Table 1).
Presence of hyporeflective areas in blue widefield SLO images in eyes with advanced diabetic retinopathy (DR)
In patients with no fundus lesions, a uniform background was observed in the blue widefield blue images (Supplementary Fig. 1). On the other hand, hyporeflective areas were present in the blue widefield SLO images in 98 of the 177 eyes of the DM patients (55.4%; Figs. 1–5, Table 2). A hyporeflective area was easily recognized as an area of darker appearance than the surrounding areas. In some areas, the retinal vessels crossing the hyporeflective area were seen as white lines (Fig. 1–5). Hyporeflective areas were found in 72 of 94 eyes with PDR (76.6%), in 26 of the 53 eyes (49.1%) with moderate to severe NPDR, and none of the 30 eyes (0%) with less than mild NPDR. The hyporeflective areas were either localized or diffuse. Among the 72 eyes with PDR that had hyporeflective areas, 63 eyes (87.5%) had a history of PRP. In these 63 eyes, hyporeflective areas were observed both in eyes with and without prior PRP (Figs. 1–5).
Among the control patients, hyporeflective areas were not found in the blue SLO images in any of the 56 eyes with any fundus diseases other than in eyes with RVO. However, hyporeflective areas in the blue SLO images were seen in 4 of 7 (57.1%) eyes with a BRVO (Table 2). None of the 36 control eyes with fundus disorders had hyporeflective areas.
Concordance of hyporeflective areas in blue widefield SLO images and non-perfused areas (NPAs) in fluorescein angiograms (FA)
FA images were available for 175 eyes; 126 eyes in the DM groups and 49 eyes in the non-DM controls. In the DM group, 70 of the 94 eyes with PDR had FA images, 46 of the 53 eyes with moderate to severe NPDR had FA images, and 10 of the 30 eyes with less than mild NPDR had FA images. Among the 49 eyes of the non-DM controls, FA images were available in 6 of the 7 eyes with BRVO, 35 of the 56 eyes with fundus disorders except DR or RVO, and 8 of the 36 eyes with non-fundus disorders.
Among the eyes examined by FA, NPAs were found in 65 eyes with PDR, in 27 eyes with moderate to severe NPDR, and in 3 eyes with BRVO. In these cases, a concordance in the incidence and location between the hyporeflective area in the blue SLO images and the NPAs in the FA images was evaluated (Table 3). Among the 65 eyes with PDR in which NPAs were found in the FA images, hyporeflective areas in the blue SLO images were observed in 53 eyes (52/65, 80.0% sensitivity). Similarly, in 27 eyes with moderate to severe NPDR and with NPAs in the FA images, the hyporeflective areas in the blue SLO images were found in 21 eyes (21/27, 77.8% sensitivity). In these eyes, the location of the hyporeflective areas corresponded exactly within the location of the NPAs in the FA images (Fig. 1–5). In contrast, 13 of the 65 eyes (19.7%) with PDR and with NPAs in the FA images and 6 of the 27 eyes (22.2%) with moderate to severe NPDR and with NPAs did not show hyporeflective areas in the blue SLO images. In these eyes, the SLO images were obtained after photocoagulation, while the FA images were obtained before the treatment. Thus, the chorioretinal scars of photocoagulations seemed to interfere with finding the dark areas with multiple scars showing hyperreflection. In 3 eyes with BRVO and with NPAs in the FA images, the hyporeflective areas were detected in all 3 eyes (3/3, 100% sensitivity). In these 3 eyes, the hyporeflective areas corresponded with the areas of the NPAs in the FA images (Supplementary Fig. 2).
In contrast, none of the eyes without a NPA in the FA images (10 eyes with less than mild NPDR, 3 eyes with BRVO, 35 eyes with other fundus diseases except DR/RVO, and 8 eyes without fundus diseases) showed any hyporeflective areas in the blue widefield SLO images.
The concordance between the incidence of hyporeflective areas in the widefield blue SLO and the NPAs in the FA images was determined by calculating Cohen’s kappa coefficient (κ) with the kappa function. The mean κ value was 0.785 with a range of 0.6 and 0.8. Thus, we conclude that there was good concordance in the incidence (Table 3). Furthermore, hyporeflective areas were not found in the blue SLO images, when NPAs in the FA images were not found, in all 80 eyes for a specificity of 100%. Thus, the concordance relationship between the widefield blue SLO images and the NPAs in the FA images was very high.