Non-comitancies based on paretic EOMs are traditionally considered clinically significant only when they exceed a 5^ difference in various positions of gaze. But it’s the subtle differences, typically less than 5^, that interest us here. And that is my contention that the Three Step maneuver I described in Parts 1 and 2 best tease that out in real space.
Let’s presume the patient shows a subtle vertical phoria in primary gaze, and tests positive for diplopia on the Worth 4 Dot only in down gaze but not in primary or upgaze. We then isolate a horizontal line at distance and look at the vertical vergence range.
You can do this the same way you look at horizontal vergence ranges, using a vertical prism bar. But for the purposes of Rxing prism, I’m more interested in a loose vertical prism differential. We’re basically looking at jump vertical vergence, or vertical vergence facility. You would expect that if the patient measures a 2^ R Hyperphoria on Red Maddox Rod testing in free space, he would find it much easier to fuse 2^ BD over the R eye and report discomfort or diplopia on 2^ BU.
Let’s presume you find that vertical disparities as measured by phoria, fixation disparity or any other means (e.g. cheiroscopic tracing) don’t respond differentially to prism jumps in the BU or BD direction. That’s where the Press Three Step applies to Rxing yoked prism to move the patient toward the field of most comfortable fusion (U/D, L/R, or Oblique).
Lastly we use the Three Steps (we could just as easily call it the six positions, but the name’s not as catchy) to monitor the range of motion developed through therapy. In this regard we dovetail with what is done through Vestibular Rehabilitation Therapy (VRT). In this regard, we combine binocular awareness and feedback with head and neck rotations. Thumb rotations and head rotations are VRT versions of what the old masters did in OVT, but it’s crucial in transferring these skills to ADLs to incorporate awareness of fusion.
We’ve addressed this previously with Brock String in various positions of gaze, where changing the angles integrates the VOR with EOM alignment. We’ve also addressed the importance of doing free space fusion with targets such as eccentric circles in 360 degree arcs, and with the targets torqued to gain symmetry, in order to maximize cyclofusional vergence ranges. To this we’re adding head rotations in the three planes to actively spread comitance and symmetry, integrating COR with VOR and EOM alignment. Changes made in doing this with Brock String, ECs, Life Savers, etc. in free space should show up as improved symmetry on the Press Three Step Test.