Proposed Mechanism
With the rising reports of blindness secondary to soft tissue augmentation, the understanding of the mechanism of this complication has evolved. It has been suggested that vascular complications such as blindness can be attributed to intravascular injection and retrograde embolization of the filler.47 Although it may seem logical that the material injected into an artery would flow in the direction of blood flow, in fact, the arteries branch and become smaller more distally, whichincreases resistance. Arapidlyinjected bolusmayfindlessresistanceproximallythandistally. It has been shown that arterial pressure can be easily overcomewheninjectingandthematerialcantravelin a retrograde fashion.48 Multiple branches of the
ophthalmic artery project outside the ocular area and onto the nose and forehead. Proximal branches include the supraorbital, supratrochlear, and dorsal nasal artery. Furthermore, there are anastomoses between many other arteries of the face and those branches of the ophthalmic artery. If the tip of the needle or cannula penetrates the vessel and enough pressure is applied to the plunger when injecting even small volumes of filler, the arterial pressure can be overcome and the filler can reach the ocular vessels. When the injector stops the pressure of injection, the arterial pressure can carry the embolus from the proximal vessels such as the ophthalmic artery to the more distal retinal arteries. Because these are small arteries,alargevolumeoffillerisnotrequiredtocause occlusion. Indeed, many of the reported cases have involved injections of 0.5 mL or less.48 If the injector applies greater pressure for longer, there is a chance that the filler may travel retrograde into the internal carotid artery and from there may advance into the cerebral circulation, causing a stroke.47