The 3-step test. A, Step 1: A right hypertropia suggests weakness in 1 of the 2 depressors of the right eye (RIR or RSO) or in 1 of the 2 elevators of the left eye (LIO or LSR). B, Step 2: Worsening of the right hypertropia on left gaze implicates either the RSO or the LSR. Note that at the end of step 2, 1 depressor and 1 elevator of opposite eyes will be identified as the possible weak muscle. C, Step 3: The right head tilt causes intorsion of the right eye. Because this rotation depends on activation of both the RSO (a depressor) and the RSR (an elevator), weakness of the RSO will cause the right hypertropia to increase.