. The patients were transferred to the operating table for measurement of bilateral rSO2, and preoxygenation was performed for three minutes using 4 L/min 100% oxygen via nasal cannula. The basal oxygenation values were determined by taking the average of the last 30 s measurements. The rSO2 values were recorded at 1, 3, 5, 10, 15, 20, 25, 30th, 35, 40, 45, 50, 55, and 60 minutes after retrobulbar block, and at 10, 20, 30, and 40 minutes after the completion of the procedure.