I have had episodes of transient diplopia for about seven years..i recently went to an opthamologist and everything checked out okay. what could it be?

Unbalanced: Autonomic (automatic) nervous systam affecting the control mechanisms of the eye muscles. I would expect other symptoms that you might "take for granted". It is possible that diet has introduced a vitamin deficiency because that affects that nervous system.

Diplopia: Many things, but most likely congenital meaning it has been there since birth and is becoming manifest now.