Early Onset Sixth-Nerve Palsy with Eccentric Fixation

To report four cases of early onset sixth-nerve palsy all of whom had eccentric fixation.

A retrospective case note review was undertaken of all cases presenting to the senior author's private and NHS practice with early onset sixth palsy between 2006 and 2012. As well as demographic information, details of ophthalmic, orthoptic, electrophysiological examinations, and radiological investigations that were extracted from the records.

Four children with unilateral or asymmetric early onset sixth-nerve palsy were identified, of which three were congenital. All four had MRI and only one had a normal MRI. Age at presentation ranged from 14-42 months, but all four had marked esotropia and poor visual acuities in the worst affected eye with eccentric fixation, which became more easily or only noticeable after surgical correction. Three patients with congenital sixth-nerve palsy underwent vertical muscle transposition with Botulinum Toxin A (BTXA) to the ipsilateral medial rectus, and two of these patients also had Foster sutures to the transposed vertical muscles. The fourth patient had unilateral medial rectus recession and lateral rectus resection. The mean preoperative measurement was 55^Δ ET (range 50-60^Δ), and the mean postoperative measurement was 11^Δ ET (range 16XT-25ET) at near, and 2^Δ XT (range 15XT-14ET) at distance.

We speculate that early onset paralytic strabismus due to congenital sixth-nerve palsy results in an inability to cross fixate which results in the development of eccentric fixation. Attempts to use reverse occlusion to negate the eccentric fixation failed. We therefore recommend early surgery for this condition to avoid this sequelae.