Placing fillers, such as Restylane, in the tear trough is an off label use of these products. However, it is a common location for filler injection and it works wonders on hollowness of the tear troughs. An extremely rare complication of injections perfomed around the eyes is blindness. Although I don't know of any studies looking at the rate of this complication with needles versus cannulas (it would be a hard study to do because this complication is so uncommon), I suspect that using a cannula would be less risky because there is a lower risk of puncturing a blood vessel. Using a cannula decreases discomfort and bruising with filler injection but is not as precise as using a needle. Many filler injectors will use both cannulas and needles to get the best results. I would recommend seeing a physician who is comfortable with injecting filler around the eyes and defer to their preference in treating this area.
Thank you for the question. As others have said, the risks are quite low with needle injection -- and are even lower with cannulas. In my practice, I prefer to use Derma-Sculpt cannulas for my tear-trough injections because I find that the patients have a more comfortable experience and less bruising afterward. There are lots of tiny veins in the eyelid, and using a blunt cannula helps to avoid nicking one of these. I also have all patients use ice packs and avoid strenuous activity for 24 hours after injections around the eyes. Best of luck moving forward!
The decision on whether to use a cannula or needle for tear trough injections is really doctor preference. The risk of blindness from tear trough injections is very low. There are only a handful of cases of this type of complication reported in the world medical literature even though tens of thousands of people have had this procedure done. The risk is not zero, but is definitely very low. Each patient needs to consider this before having any type of filler injections.
There is a risk of vision loss from filler injections outside the eye area as well. There are reports of vision loss after filler injections in the glabella (area between the eyebrows) and even in the smile lines. Again, the risk of this type of complication is very low.
The idea that cannulas are safer than needles for tear trough injections is purely theoretical, and not based on real world clinical studies. In my own practice, I perform multiple tear trough injections each week and use needles exclusively. I find that I can get a much nicer result with a needle than with a cannula. With a needle, I can place the injections at the exact depth that I want to, which I feel is often difficult when I have tried using cannulas in the past.
My advice would be to go to the doctor who has the most experience with tear trough injections. You should never feel bad about asking your doctor how many times they have done a particular procedure.
Best of luck!