We would like to present a case of branch retinal artery occlusion following uneventful phacoemulsification, possibly caused by sub-Tenon's anaesthesia. There were no predisposing general health problems. There are two possible mechanisms: (1) mechanical effect of the bolus anaesthetic; (2) pharmacologically mediated changes in the vascular calibre. The latter mechanism is much more probable, because of the vasoconstrictive properties of both medications used. This is the first reported case of branch retinal artery occlusion after sub-Tenon's anaesthesia with preservative-free medications.