Retinal Oxygen Delivery and Metabolism in Healthy and Sickle Cell Retinopathy Subjects

PURPOSE: Reduction in inner retinal oxygen delivery (DO(2)) can cause retinal hypoxia and impair inner retinal oxygen metabolism (MO(2)), leading to vision loss. The purpose of the current study was to establish measurements of DO(2) and MO(2) in healthy subjects and test the hypothesis that DO(2) and MO(2) are reduced in sickle cell retinopathy (SCR) subjects. METHODS: Dual wavelength retinal oximetry and Doppler optical coherence tomography were performed in 12 healthy control and 12 SCR subjects. Images were analyzed to measure retinal arterial and venous oxygen content (O(2A) and O(2V)), venous diameter (D(V)), and total retinal blood flow (TRBF). Retinal arteriovenous oxygen content difference (O(2AV)), DO(2), MO(2), and oxygen extraction fraction (OEF) were calculated according to the following equations: O(2AV) = O(2A) − O(2V); DO(2) = TRBF * O(2A); MO(2) = TRBF * O(2AV); OEF = MO(2)/DO(2). RESULTS: Retinal D(V) and TRBF were higher in the SCR group as compared to the control group, whereas, O(2A), O(2V), and O(2AV) were lower in SCR group as compared to the control group. DO(2), MO(2), and OEF were not significantly different between control and SCR groups. MO(2) and DO(2) were linearly related, such that higher MO(2) was associated with higher DO(2). There was an inverse relationship between TRBF and OEF, such that lower TRBF was associated with higher OEF. CONCLUSIONS: Increased blood flow compensated for decreased oxygen content, thereby maintaining DO(2), MO(2), and OEF at predominately lower stages of SCR. Quantitative assessment of these parameters has the potential to advance knowledge and improve diagnostic evaluation of retinal ischemic conditions.