• #2-3. Pathogenesis of Blindness Caused by HA Fillers


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    Pressure and Volume of Fillers, and the Risk of Blindness


    There are the two most important elements of fillers in terms of the risk of blindness. The first element is how intense pressure is applied for injection. In other words, it is related to the pressure on the syringe during a filler procedure. The second element is how much filler is injected at one time, which is related to volume.


    In fact, the concepts of pressure and volume are not different but correlated. The stronger pressure is applied for injection, the more volume of filler is injected. On the other hand, when the filler is gently injected at a low pressure, the volume of the filler injected at one time becomes small.


    The process of blindness due to filler injection is summarized as the following five steps:


    1. The blood vessel (connected to the ophthalmic artery) is pierced.


    2. The needle tip or cannula tip must be located in the blood vessel.


    3. The needle or cannula must fill the blood vessel.


    4. The filler must be injected under sufficient pressure (larger than the ophthalmic artery pressure). 


    5. A sufficient volume of filler must be injected


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    1.  A sufficient volume of filler must be injected


    The needle is more likely to pierce blood vessels than the cannula. In particular, needles with a small diameter can most easily pierce blood vessels because the pressure applied when piercing blood vessels is low. Even large-diameter needles may pierce blood vessels, but it is easier to rupture blood vessels if the diameter of blood vessels is smaller. Although the probability is low, fillers may move through such torn blood vessels.


    When the filler is injected with a large-diameter needle, the bolus of filler to be injected may be large, and the fibrosis of skin tissue may progress after the filler procedure, which may cause vascular events due to the reduced vascular movements during the next filler procedure. In addition, inflammatory response due to tissue damage is highly likely to result in granuloma by causing the initial immune response of fillers.


    Although the cannula is less likely to pierce blood vessels, the likelihood may be high if blood vessels are fixed with reduced movement due to fibrosis of the surrounding tissue (plastic surgery or previous filler or thread lifting procedures on the surrounding tissue) and the diameter of blood vessels becomes larger.


    In addition, as for inexperienced injectors who are not well acquainted with anatomical structure of tissues or blood vessels subject to procedure and are not proficient in performing a procedure, they may penetrate blood vessels during a procedure.


    Therefore, the injectors must distinguish the degrees of resistance in penetrating a tissue and then discontinue the procedure if the resistance more than a certain level of intensity is felt and lower the possibility of penetration into blood vessels by reassessing the tissue. Particularly, surgeons with little experience should be careful when performing a procedure with a large-diameter cannula. Usually, procedures are performed on the assumption that large-diameter cannulas can hardly penetrate blood vessels. 


    However, if the procedure is carried by the injector who is not skilled and a excessively large bolus of filler material is injected, even a large-diameter cannula may cause blindness. To prevent blindness, the injector needs to concentrate on practicing filler injection with a single procedure tool, whether it is a needle or a cannula, and should be able to distinguish the tissues felt through the tool.


    - To be continued

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