The authors present two case reports for the rare, but serious, complication of retinal vascular occlusion as a presumed result of subconjunctival injection following 25-gauge vitrectomy. Risk factors for the complication include: cardiovascular disease, retrobulbar anaesthesia, high intraocular pressure (IOP) perioperatively, and drug toxicity. Case 1 presented a 61-year-old man with a stage 2 macular hole in the right eye, no systemic diseases and a normal IOP. Following retrobulbar anaesthesia and SF6 gas tamponade, subconjunctival gentamicin was administered. On postoperative day (POD) 1, temporal sided dot haemorrhages were observed and on day three no signs were observed resulting in discharge. Upon fundus examination on POD10 there was retinal whitening in the macula and cotton wool spots and a reduction in visual acuity to hand motion. Fluorescein angiography (FA) confirmed occlusion of the macular branch retinal artery on the inferior temporal side. Antiplatelet and vasodilator therapy coupled with an oral steroid were prescribed and a stellate ganglion block was performed to increase ocular circulation. The macular hole was closed with a slight improvement in visual acuity but below preoperative level. Case 2 highlighted the treatment of a 51-year-old woman with visual acuity reduction in the right eye as a result of retinal tears. Following vitrectomy, gas tamponade, and gentamicin injection there was dot bleeding and retinal whitening in the macula on POD2. FA revealed retinal vein filling defects around the macula. A urokinase infusion and oral acetazolamide made no improvement in retinal circulation. Optical coherence tomography one year later confirmed a highly damaged superficial and deep capillary plexus. Previous reports have documented subconjunctival gentamicin-induced macular toxicity following sutureless 25G vitrectomy. Primate experiments involving retinal gentamicin injection have shown inflammatory changes in the inner layer of the retina and vascular occlusion due to granulocyte plug formation around the capillary bed. As hypotony and wound leak encourage gentamicin entry into the vitreous fluid, the authors sutured the ports and measured IOP intraoperatively. There has been no evidence reported that prophylactic antibiotic injection prevents endophthalmitis after vitrectomy. Nonetheless, gentamicin induction of retinal vascular occlusion remains an important complication despite sutured ports.