This study used the optical coherence tomography angiography (OCTA) technique to evaluate possible hemodynamic changes after horizontal rectus muscle surgery in 32 eyes of 16 patients; nine male, seven female. Recession / resection surgery was undertaken for two horizontal rectus muscles in one eye. Mean age was 35.7 ±12.9 years. There were eight esotropias and eight exotropias. Postoperatively there was a significant increase in measurements of vessel density of the superficial and deep capillary plexus for operated eyes. There were no significant changes for fellow non-operated eyes. A significant decrease was noted in superficial and deep foveal avascular zone measurements. The authors propose these changes were caused by surgery and not by other factors such as anaesthesia. Potential explanations for changes may be inflammatory reaction due to surgery or increased blood flow as a compensatory mechanism with anterior ciliary artery injury. This warrants further study.