Retinal Blood Oxygen Saturation and Angiogenic and Inflammatory Biomarkers in Type 2 Diabetes
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Introduction: Diabetic retinopathy (DR) is a major source of visual loss in the world, including North America. A number of hyperglycemia-related pathways have been associated with DR onset and progression. Disturbances in the retinal vasculature appear to play a vital role in DR, resulting in biochemical and functional vascular changes. Therefore, this study investigated retinal blood oxygen saturation and angiogenic and inflammatory biomarkers in DR. Methods: Chapter 3 and 5: FD-OCT Doppler blood flow was non-invasively measured using a prototype system based on the RTVue (Optovue Inc., USA). A minimum of six separate FD-OCT Doppler measurements was acquired. Chapter 4, 5, 7: Non-invasive hyperspectral retinal (HR) imaging was acquired in participants with mild-to-moderate NPDR and age-matched controls. For each subject, six repeated HRC images were acquired at wavelengths of 586 and 605nm. Results: Chapter3: The individual COV medians for retinal blood flow were 7.5% and 9.2% for young and elderly subjects, respectively. The group mean CORs for retinal blood flow for young participants were 6.4µl/min and for elderly subjects were 10.5µl/min. Chapter 4: Retinal blood oxygen saturation in the arterioles of healthy controls was 92.97±1.6%, and in the venules was 55.90±4.8%. Retinal blood oxygen saturation for diabetic subjects with NPDR was significantly higher at 94.65±2.2% (p=0.015) in the arterioles and 64.13±4.3% (p<0.001) in the venules. Chapter 5: Total retinal blood flow was significantly lower in NPDR when compared to controls (42.66 vs 32.97; p=0.004). There was no relationship between total retinal blood flow and venular oxygen saturation (r=0.2). Chapter 6: Angiopoietin 2, IL-8, HGF was significantly higher in NPDR patients than in control patients (p=0.005, p=0.034, p=0.018, respectively) and EGF was significantly lower in NPDR patients when compared to controls (p=0.025). Chapter 7: The study demonstrated a correlation between retinal blood oxygen saturation and Ang 2, HGF and EGF but did not find any correlation for IL-8, TGF-β even though these biomarkers were significantly higher in the diabetic group. Conclusions: Chapter 3: Doppler OCT gave consistent and repeatable blood flow measurements within retinal venules in normal subjects. Chapter 4: A higher blood oxygen saturation could be the result of less oxygen consumtion due to cell death. Chapter 5: There is no correlation between retinal blood flow and retinal blood oxygen saturation. Chapter 6: Further investigation of Ang 2, HGF, IL-8, EGF, TGF-β could be used to better understand the pathophysiology of DR. Chapter 7: The result of this study revealed a relationship between the biomarkers that might result in cell death and higher retinal blood oxygen saturation.