Does too much masturbation cause blindness?

No: I am very sorry somebody told you something this foolish. Whoever told you this is either extremely ignorant, or is trying to frighten you for their own dark purposes. I hope that in the future you are able to avoid these people. Talk with your personal physician about your changing body -- or a sensible adult, maybe even your same-sex parent.

No: Masturbation is a normal part of human sexuality.Some cultures frown on the process & develop such myths to suppress it. Most seldom discuss it openly. If anyone does so to the exclusion of interacting with people ; pursuing age ; peer related activities, it can interfere with normal emotional growth, as any preoccupation might. For most, it is simply part of their life.