Al is correct, 3 years for QC1 or working to AWS D1.1 as an inspector.
However many employers have their QC manual written to require Acuity Eye Exams annually for the inspectors. Also if your employer does any NDT, ASNT SNT-TC-1A says that the employer shall have a written practice, and many times the NDT Level III will draft the written practice to say that annual eye exams will be on file for all inspectors.