Therefore, the combination of reduced innervation to the elevator muscles and intact innervation to both depressor muscles causes the healthy contralateral eye to develop a secondary hypotropia when the paretic eye is in fixation duress.2 A common clinical mistake in the examination of diplopia is to assume that the deviated eye must always be the paretic one. The PET study did, however, demonstrate focally increased SP 18 sp F-FDG avidity within the structurally-normal IR muscle of the paretic left eye. [Extracted from the article]