Hi Kriston,
A plain ol' optometrist diagnosed both of my dds' vison problems. My youngest wasn't even consistently recognizing her letters at four. I was "there, there'd" by many people, and told that I shouldn't compare her to her sister. All four year olds should have their vision and hearing tested, so I used that as my excuse to have her vision and hearing tested. What really prompted me was that she was having trouble reading. When I shared my concern with the optometrist he explained that it was physically impossible for her to focus on letters because of her severe near-sighted/far-sighted astigmatism. I simultaneously felt justified in my concern and was kicking myself that I did not act on my gut-instinct sooner.
DD9 got glasses recently. She has 20/20 sight when tested with the standard eye chart (like they use for vision testing in school). She was complaining that it was hard to read. After a full battery of tests, the optometrist found that she was slightly far-sighted. He said that what she has is difficult to identify because most children do not complain about it. The optometrist said that many children with the same problem just avoid reading. Since my dd loves to read, she wanted the problem fixed.
Ironically, my youngest dd never complained about her severe vision problem.
I hope things go well with your optometrist visit and you have your questions answered. At the very least, I think you can feel confident that it is a good first step.