On the other hand, I may suggest explaining to your parents that:
if you couldn't see clearly, say your vision was blurry, they would take you to the eye doctor for an exam? would they?
if yes, then why won't they at least take you to talk to some one about how you are thinking and how it affects your daily life?
To bring the illustration further:
it could be up to the eye doctor to decide if you need glasses and if so to what degree or maybe just eye drops?
Sometimes the eye doc will even say we need to adjust our health habits (maybe) to improve our vision....same with our mental health
But, if your parents don't ever want you "wearing glasses", you probably won't be able to get to the "eye" doctor until you are old enough to go on your own.
Try to be as responsible as possible in every way you can to show them how serious you are if you really want help. This should show them you are sincere and mature.