a 74-year - old lady presented to our clinic complaining of progressive blurred vision more in the right eye ( re ) compared to the left eye ( le ) , over the last 6 months . past medical history showed transsphenoidal pituitary surgery ( 16 years ago ) , acromegaly , well - controlled hypertensive disease and hyperlipidaemia . on routine follow - ups and mri scan after the neurosurgery , no recurrence or abnormalities in the visual field were noted . ophthalmological examination showed best corrected visual acuity ( bcva ) 0.5 ( 6/12 ; 20/40 ) in the re and 0.7 ( 6/9 ; 20/30 ) in the le . anterior segment was normal with exception of nuclear cataracts in both eyes ( be ) , more pronounced in the re compared to the le . preoperatively g. tropicamide 1% , g. phenylephrine 2.5% , g. cyclopentolate 1% and g. oxybuprocaine 0.4% were instilled in the re . sub - tenon 's anaesthesia with lidocaine 2% ( 2 ml ) , bupivacaine 0.5% ( 3 ml ) and hyalase was performed in the lower nasal quadrant of the re . uneventful phacoemulsification with implantation of posterior chamber intraocular lens was performed by an experienced surgeon ( consultant grade ) in less than 15 min . during the surgery intracameral cefuroxime 1 mg and subconjunctival mixture of cefuroxime and betnesol subconjunctivally were injected at the end of the procedure . the eye was left with normal intraocular pressure ( iop ) after the closure of the wound . acetazolamide 250 mg once in the night after the surgery were prescribed . during the procedure the highest level of blood pressure recorded was 135/95 mm hg and all other parameters monitored were within normal limits ( pulse , saturation , respiration ) . on the 1st postoperative day visual acuity ( va ) in the re was counting fingers ( cf ) . there were a few descemet folds in the cornea , mostly around the incision site . on the 6th postoperative day va in the re was still cf with no pinhole improvement . both pupils had brisk reaction to light and no relative afferent papillary defect was noted . on standard slit lamp . optical coherence tomography scan of the re showed increased reflectivity of the inner retinal layers and hyporeflectivity of the outer retinal layers ( fig . these findings were consistent with retinal artery occlusion . on the 9th postoperative day visual field investigation was performed and it showed central scotoma in the re , occupying 5 degrees ( fig . standard slit lamp fundoscopy showed absence of foveal reflex , but no other major abnormalities . the same investigation performed with red - free filter showed pronounced macular nerve fiber layer oedema with relative foveal sparing in the re ( fig . 1b ) . on the fluorescein angiography performed on the same day , a small retinal artery branch , crossing the horizontal raphe , with very irregular lumen surprisingly the bcva in the re improved to 0.3 ( 6/18 ; 20/60 ) and 0.5 ( 6/12 ; 20/40 ) on the 2nd and 4th week after the surgery , respectively . there are several case reports , describing central artery occlusion ( crao ) after cataract surgery , vitrectomy , pterygium excision and other ophthalmic procedures . all these procedures were performed under local anaesthesia , particularly retrobulbar , parabulbar or sub - tenon 's anaesthesia . there are different possible mechanisms : ( 1 ) mechanical effect of the bolus anaesthetic ; ( 2 ) pharmacologically mediated changes in the vascular calibre . the mechanical effect of bolus anaesthetic may cause elevation of iop or direct pressure over the vessels . several studies done on the effect of sub - tenon 's anaesthesia on iop show that there is no significant increase in the iop [ 1 , 2 , 3 ] . this is thought to be one of the advantages over other types of peribulbar anaesthesia , where more pronounced iop elevation was detected [ 1 , 2 , 3 ] . this may be because when sub - tenon 's anaesthesia is performed the incision in the conjunctiva may allow egress of fluid if the pressure is too high . the bolus pressure over the vessels is thought to be insignificant , because in the sub - tenon 's space a thin layer of anaesthetic is formed . neither honan 's balloon , nor digital massage were used , in which cases the iop may be increased significantly to a level sufficient to occlude the central retinal artery [ 4 , 5 ] . the iop may increase more significantly in patients with glaucoma   or other conditions , associated with deficient blood supply to the optic nerve . the pharmacologically mediated changes in the vascular calibre are the more likely mechanism in which retinal artery occlusion can occur . meyer et al .   have shown in a study performed on porcine ciliary artery that local anaesthetic agents of the amide type such as lidocaine , bupivacaine and mepivacaine interact with the vascular endothelium . this effect is mediated via receptor - operated activity of the endothelial l - arginine / nitric oxide pathway . .   showed that after peribulbar anaesthesia pulsatile choroidal blood flow and retinal blood flow velocities were reduced . this effect was still present 5 min after the anaesthesia , when the iop had returned to baseline . .   demonstrated that ocular pulse amplitude was significantly reduced when lidocaine was used either as sub - tenon 's or peribulbar anaesthesia . it is known that lidocaine in low concentration causes vasodilation , but in higher concentrations vasoconstriction can occur . in the sub - tenon 's group of this study , because of the systemic absorption there was noted increased ocular pulse amplitude in the fellow eye in the 1st minute after the injection and reduced in the 10th . this was explained with the lower dose early and the higher dose of systemic lidocaine reaching later on the other eye . because the amount of anaesthetic used in this study was relatively small ( 2 ml lidocaine ) another possible cause for branch retinal artery occlusion ( brao ) after sub - tenon 's anaesthesia is presumed toxic effect from preservatives contained in the vials with anaesthetic drugs . there are 3 published cases of brao and 3 cases of crao after sub - tenon 's anaesthesia prior to vitrectomies with mepivacaine containing methyl- and propyl parahydroxybenzoate over a period of 3 months . these vascular effects occurred between 2 and 14 days after the anaesthesia , which makes the toxic effect more probable in comparison with vasospastic effect . in our case it is believed that the cause of visual loss in this patient is spasm of a branch of the central retinal artery , which led to occlusion . three cases of transient crao after sub - tenon 's anaesthesia were published by feibel and guyton . crao is a possibility in our case as well , but the absence of relative afferent papillary defect , small central scotoma , localized vascular changes in the macular area and the subsequent improvement in visual acuity , make brao more probable . to our knowledge this is the first reported case of brao after sub - tenon 's anaesthesia with preservative - free medications .
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 .