Anti-wrinkle injections relax muscles. Once a muscle is relaxed, it prevents the muscle from contacting, which, over time, causes fine lines to get deeper. They will prevent the wrinkles from getting any worse, and they may also improve existing wrinkles, as the muscle isn’t contracting, anymore.
Anti-wrinkle injections usually last up to 3-4 months, and then they completely wear off, and the muscle contraction will go back to exactly how it was prior to injections. Therefore, if you would like to continually prevent crows feet wrinkles from getting deeper, long-term, you will have to have repeated injections.