Hi, Joshua—All three sentences are incorrect, for a variety of reasons. The problem all three of them have is that they use the present tense form "start" to talk about something that happened in the past. "Started" is needed.
With that change alone, only (3) would be correct. Regarding (1) and (2), you can't say that you were studying MBA, since MBA stands for a degree, not a subject matter of study. You can say "studying for my MBA."
Sentence (1) has the additional problem of "when started studying." Since "started" is there a finite verb (past tense) rather than a past participle, you cannot use a reduced clause. You can use a reduced clause in (2) and (3):
(2a) I started wearing glasses when studying for my MBA.
(3a) I started wearing glasses when doing my MBA.