BACKGROUND: Blindness or visual loss is the most serious complication resulting from facial hyaluronic acid (HA) injection. In this study, three recent clinical cases were analyzed, and the relevant anatomy of cadavers was evaluated to investigate the mechanism behind visual impairment due to HA injection. METHODS: Three patients with different extents of visual loss after HA injection were studied. Ophthalmic testing and corresponding treatments were performed, and the clinical progress was observed. In addition, thirty-six fresh Asian cadaver hemifaces were anatomized to investigate the morphology of the ophthalmic artery and its branches. The minimum dose of HA for central retinal artery embolism was calculated based on the ophthalmic arterial volumes of cadavers. RESULTS: Visual impairment was more severe in central retinal artery occlusion and combined intraocular branch occlusion than in posterior ciliary artery occlusion. During follow-up, no improvement was observed in terms of visual impairment. Cadaver study reconfirmed that the ophthalmic artery included facial and intraocular branches. The ophthalmic arterial volumes running from the supraorbital artery and supratrochlear artery to the central retinal artery were 0.083 cm and 0.089 cm, respectively. CONCLUSIONS: The severity of blindness caused by HA injection may be associated with the occlusion site. Our clinical observations indicate that conventional treatments, such as retrobulbar hyaluronidase injection, are insufficient to relieve visual impairment. Injecting as little as 0.08 ml of HA into the facial branch is enough to cause central retinal artery embolism. Limiting the volume per injection could represent a simple prophylactic strategy. LEVEL OF EVIDENCE V: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .