How long will canthoplasty results last?

A canthoplasty is designed to last a long time. it corrects the laxity in the lower lid ligament which took years to develop. It is unusual to go back and have to redo a canthoplasty.

Canthoplasty usually can last a long time, but there are some issues that can be difficult to treat with canthoplasty. Specially, medial canthoplasty to correct punctal eversion. These type of problems are difficult to treat even with medial canthoplsty. So I should say depend on why the canthoplasty was performed the longavity of cahtoplasty my differ. 

Relaxation of the canthus is one of the things that happens to the eyes with age. A canthoplasty is designed to correct this. It is usually accompanied by a Blepharoplasty to also tighten the shin and remove the tear troughs. It usually lasts many years. Most people need it only once.