INTACT BINOCULAR FUNCTION AND ABSENT OCULAR TORSION IN CHILDREN WITH ALTERNATING SKEW ON LATERAL GAZE

Background: A form of skew deviation, called alternating skew on later al gaze, resembles bilateral superior oblique overaction. Oblique musc le overaction has been recently speculated to result from loss of fusi on with subsequent ''free-wheeling'' of the torsional control mechanis ms of the eyes, causing sensory intorsion or extorsion with attendant superior or inferior oblique muscle overaction, respectively. We wante d to investigate whether loss of fusion plays a role in the pathogenes is of alternating skew on lateral gaze. Subjects and methods: We exami ned seven consecutive patients with posterior fossa tumors, enrolled i n a multi-disciplinary pediatric neuro-oncology program, who displayed alternating skew on lateral gaze. All patients underwent a thorough o phthalmologic evaluation. Results: Visual acuities in the study patien ts ranged from 20/20 to 20/40. Five of the seven patients were orthotr opic, and showed 40 sec of arc stereopsis. Three patients showed assoc iated downbeat nystagmus. No ocular torsion was found in any of the fi ve patients who showed normal stereopsis upon inspection of fundus lan dmarks on indirect ophthalmoscopy. Conclusion: Patients with alternati ng skew on lateral gaze often have normal binocular vision and stereop sis, and lack ocular intorsion so typical of superior oblique overacti on. Alternating skew on lateral gate is neurologically mediated, with no role for defective fusion in its pathogenesis.