If I get Juvederm to improve the appearance of temple veins, how likely am I to go blind?

Hello,We don't recommend filler in the forehead to camouflage a large vessel if indeed it's the forehead you are referring to.  However, if you have more noticeable veins in the temples, using dermal filler in this area works well in camouflaging the condition.  With regards to safety, using a gel filler such as Restylane LYFT is much safer than a more viscous product that cannot be dissolved.  In our practice, we only use  the gel fillers or Sculptra for a long-term benefit.  In addition, a safe injector practices good technique to confirm that he/she is not injecting into a major blood vessel.  The secondary concern is too much product or swelling compressing a major blood vessel - using  a gel or Sculptra is much safer in this regard.  The below link offers more information and photos on how to safely and effectively treat the "temporal hollows."

Fillers can be used to lighten the visibility of veins in temple region but i usually don't do fillers for that purpose since I can treat veins in that area with sclerotherapy or laser. Risk of blindness is very minimal with fillers almost close to zero. 

The best treatment for veins in this area is laser.  However, fillers and fat can be used to "camouflage."  Sometimes with HA fillers the veins get more prominent from the water retention.  Please see an expert.  Best, Dr. Emer.