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Clinical Sciences
September 1999

Vertical Fusional Vergence: The Key to Dissociated Vertical Deviation

Author Affiliations

From the Wilmer Ophthalmological Institute, The Johns Hopkins University School of Medicine, Baltimore, Md.

Arch Ophthalmol. 1999;117(9):1188-1191. doi:10.1001/archopht.117.9.1188

Objectives  To test the previous findings of Enright that disparity-induced vertical vergence is mediated primarily by the oblique muscles, and to relate this normal eye movement pattern to the eye movement pattern seen in subjects with dissociated vertical deviation.

Methods  Sixteen normal volunteers underwent 55 measurements of the cycloversion associated with prism-induced vertical vergence using an afterimage apparatus. A Vernier scale measured the direction and magnitude of the torsional shift that occurred with recovery of fusion on removal of a 3– or 4–prism diopter prism.

Results  Of the 55 trials, the directions of torsional shift were consistent with the oblique muscles being the primary mediators of vertical fusional vergence in 51 (93%) (P=.03 using a binomial distribution). The mean±SD value of torsional shift was 1.15°±0.76° in the expected direction.

Conclusions  Vertical fusional vergences in this study were produced primarily by the oblique extraocular muscles. The eye movement patterns of these vertical vergences in normal subjects are qualitatively similar to those seen in recordings of patients with dissociated vertical deviation. Dissociated vertical deviation thus seems to be an exaggeration of a normally occurring eye movement pattern. The cyclovertical component of dissociated vertical deviation may help stabilize the fixing eye by damping vertical nystagmus, while the accompanying hypertropia is an incidental and undesirable side effect.