Purpose: To characterize the occurrence of diabetic macular edema and the presence of abnormal retinal fluid accumulation in nonproliferative diabetic retinopathy (NPDR).
Methods: In this two-year prospective study, a total of 122 eyes with diabetes type 2 underwent optical coherence tomography (OCT) and OCT-Angiography in association with OCT-Fluid imaging, a novel algorithm of OCT analysis allowing quantification of abnormal accumulation of fluid in the retina through low optical reflectivity ratios (LOR). Early Treatment Diabetic Retinopathy Study (ETDRS) grading for diabetic retinopathy (DR) severity assessment was performed using 7-field color fundus photography. Best corrected visual acuity was also recorded.
Results: During the 2-year follow-up, 23 eyes (19%) developed central-involved diabetic macular edema (CI-DME) and 2 eyes (2%) developed clinically significant macular edema (CSME). In the two-year period of the study, eyes that developed CI-DME showed a progressive increase in central retinal thickness (CRT) (β = 7.7 ± 2.1 µm/year, p < 0.001) and in LOR values (β = 0.009 ± 0.004 ratio/year, p = 0.027). The increase in CRT and abnormal retinal fluid, represented by increased LOR ratios, are associated with increased retinal perfusion in the deep capillary plexus (DCP) (skeletonized vessel density, p = 0.039). In contrast, the eyes with CSME showed decreased retinal perfusion and abnormal fluid located in the outer layers of the retina.
Conclusions: CI-DME and CSME appear to represent different entities. Eyes with CI-DME show increases in abnormal retinal fluid associated with increased retinal vascular perfusion in the DCP. Eyes with CSME are apparently associated with decreased retinal vascular perfusion in the DCP and abnormal fluid in the outer retina.
Keywords: Diabetic macular edema; diabetic retinopathy; retina; retinal pathology / research; techniques of retinal examination.