Choroidal structural analysis in eyes with diabetic retinopathy and diabetic macular edema-A novel OCT based imaging biomarker

Purpose To evaluate structural changes in the choroid among patients with diabetic macular edema (DME), with varying grades of diabetic retinopathy (DR), using enhance depth imaging spectral domain optical coherence tomography (EDI SD-OCT) scans. Methods A cross-sectional study was conducted on 82 eyes with DR and DME and 86 healthy control eyes. Eyes with DME were classified according to the severity of DR as per the international DR severity scale. Sub foveal choroidal thickness (SFCT) was obtained using EDI SD-OCT scans. These scans were binarized into luminal and stromal areas, to derive the choroidal vascularity index (CVI). CVI and SFCT were analyzed between the study and control group using paired-T test. Tukey's test was used to correlate the differences in CVI and SFCT between different grades of DR. Further analysis was done to look for the effect of DR severity and type of DME on CVI as well as SFCT using correlation coefficient and linear regression analysis. Results SFCT was significantly increased in eyes with DME as compared to the controls (334.47 +/- 51.81 mu m vs 284.53 +/- 56.45 mu m, p< 0.001), and showed an ascending trend with worsening of DR, though this difference was not statistically significant [ mild non-proliferative diabetic retinopathy (NPDR) = 304.33 +/- 40.39 mu m, moderate NPDR = 327.81 +/- 47.39 mu m, severe NPDR = 357.72 +/- 62.65 mu m, proliferative DR (PDR) = 334.59 +/- 47.4 mu m, p-0.09]. CVI was significantly decreased in DME with DR eyes as compared to controls (63.89 +/- 1.89 vs 67.51 +/- 2.86, p< 0.001). CVI was also significantly decreased with worsening DR (mild NPDR = 66.38 +/- 0.3, moderate NPDR = 65.28 +/- 0.37, severe NPDR = 63.50 +/- 0.47, PDR = 61.27 +/- 0.9, p<0.001). Conclusion SFCT and CVI are dynamic parameters that are affected by DME. Unlike CVI, SFCT is also affected by ocular and systemic factors like edema and hypertension. CVI may be a more accurate surrogate marker for DME and DR and can potentially be used to monitor the progression of DR.