It's mostly a money making scheme. Same with pharmacy schools. Same with audiologist. Everyone now has to have a doctorage degree. How much traning does a pharmacist need to look stuff up on a computer and count pills? Does someone that checks your hearing really need 4 years of graduate school? (I know all will argue they do much, much more).
I expect PA programs, who have gone from a bachelors degree to a master degree in about 15 years will soon be a doctorate degree as well. The longer they can keep people in school, the more money. Every college I know is building giant new buildings at an incredible rate. I'm afraid, we, the pubic, are the suckers for contining to give them more and more of our money (and the gov't money). But I guess until people stop going and/or the gov't gets out of the education business, it will continue the way it is. Some education people are getting VERY rich.
But back to optometry school, if an MD can learn the entire body in 4 years, how long should it take to learn about 2 inches of the body (meaning the eyeballs and a little brain and systemic stuff)? Schools could skip the crap you already learn in undergrad like biochemistry and the like. And they could skip all the old binocular tests that were developed 80 years ago but are never used today.
An optometrist could very easily be trained well in 2 years.