'Optician' is a very generalised term. (It's a bit like calling a pharmacist a 'chemist'). The correct term for the person who examines your eyes (and gives you a prescription) used to be an 'opthalmic optician'. However, because people used to just say 'optician', it resulted in confusion between 'opthalmic opticians' and 'dispensing opticians'. (The latter are the less-qualified people who make up the prescriptions and fit the glasses).
So the alternative term, for the more qualified job, of 'optometrist' has grown in favour because it makes it clear what type of 'optician' is being referred to.
Chris