In 40 normal adult cynomolgus monkey eyes, recession of various recti in different combinations was done to evaluate their effects on the anterior segment. These procedures were done as primary, secondary, tertiary, and fourth procedures (each separated by several weeks or months), ultimately involving all four recti in the eyes. In 11 eyes, posterior ciliary arteries (PCAs) were occluded to determine its effects on the anterior segment. All eyes were examined by slit lamp, color photography, and fluorescein angiography of the anterior segment, and tonometry, before surgery and serially thereafter during the follow-up period. These studies showed that recession of two or three recti simultaneously in different combinations produced no serious permanent anterior segment changes, although initially in some of the eyes there was transient mild-to-moderate anterior segment ischemia. Recession of four recti simultaneously as a primary procedure produced serious permanent ocular and anterior segment changes; however, when this was done as a secondary or tertiary procedure after previous recessions of three or four recti, anterior segment changes were much fewer and milder than when it was a primary procedure. Occlusion of all the posterior ciliary arteries in itself produced no important changes in the anterior segment, but when combined with simultaneous recession of both the horizontal recti, it produced serious anterior segment changes. In the light of these findings, the pattern of arterial blood supply of the anterior segment is discussed.