Why is optometry school 4 years long?

So this may come off as troll-like or inflammatory, but please excuse my ignorance. I just met a first year optometry student and talked a little about their schooling. Why on earth does it take 4 years to learn optometry? Techs can refract, OMDs do the surgery, GED grads can help patients try on glasses... what do you guys do that takes you so long to learn? 4 years is a LONG time! I am in dental school... it takes us 4 years to learn every procedure (root canals, fillings,... Why is optometry school 4 years long?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums