• Yi Pang, Kelly A Frantz, and Darrell G Schlange.
• Illinois College of Optometry, Chicago, Illinois 60616, USA. ypang@)ico.edu
• Optom Vis Sci. 2012 Nov 1; 89 (11): e72-7.

PurposeDissociated horizontal deviation (DHD), a rare subtype of strabismus, is a change in horizontal eye alignment that does not obey Hering’s law. The variation is unrelated to a change in accommodation and depends on which eye is fixating. Both esotropia (ET) and exotropia (XT) can manifest in the same patient with DHD. Surgery has been reported to manage DHD, but often a second or third surgery is necessary. We report two cases of DHD that were managed with vision therapy (VT).Case ReportsCase one: A 9-year-old girl presented for eye examination with her parents noting an eye drifting out. Cover test showed a DHD that varied from 15Δ left ET to 15Δ alternating XT. A 40Δ XT manifested when she was inattentive. Antisuppression, vergence, accommodation, and oculomotility were addressed with VT. Upon completion of VT, binocular vision functions were normal except for appreciation of global stereopsis. No strabismus was observed during the examination. These findings were stable at a 7-month follow-up visit. Case two: A 40-year-old man presented for eye examination with the complaint of double vision and eye strain. Cover test revealed a DHD that varied from 5Δ ET to 15Δ XT, along with DVD. A 30 to 40Δ XT was observed during visual inattention. Antisuppression and vergence skills were addressed with VT. At the end of VT, most binocular vision functions were normal. No strabismus was observed on cover test. Follow-up examination 16 years later showed no strabismus by cover test, although XT manifested when he was inattentive.ConclusionsIn two DHD cases, control of eye alignment improved with VT. To the best of our knowledge, these are the first case reports to describe management of DHD with VT. Eye care practitioners should be aware that a long period of VT may be necessary to successfully manage DHD.

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