[Eye muscle surgery in unilateral abducens palsy]

As there are only few data on squint angle reduction following surgical treatment of unilateral abducens palsy, we aimed to quantify squint angle reduction after several different surgical procedures.

Retrospective analysis of 88 consecutive files of patients with unilateral abducens palsy, treated in 2000 - 2007 (46 resections of the lateral rectus muscle, 25 resections of the lateral rectus combined with recession of the medial rectus, 17 Hummelsheim transpositions, modified by Kaufmann). Maximal abduction was possible up to primary position in all 17 patients with Hummelsheim transposition. All other patients (except two) were able to abduct beyond primary position.

In resections of the lateral rectus a stable dose-effect-correlation was found: the dose-effect coefficients (DEC) ranged between 1.5 degrees and 1.6 degrees reduction of horizontal angle (far fixation)/mm of resected muscle. In combined convergence procedures the DEC ranged from 1.52 degrees /mm (7-9 mm recession/resection) up to 1.39 degrees /mm (13-15 mm recession/resection). In muscle transpositions (Hummelsheim-Kaufmann), preoperative horizontal squint angle (far distance) was reduced from +29 degrees (median, range +15 degrees to +50 degrees ) to -3 degrees (median, range -15 degrees to +17 degrees ) postoperatively (6-8 weeks). The best results were achieved with preoperative squint angels between > +20 degrees and < +35 degrees . Larger basic angles showed mostly undercorrection; smaller angles showed always overcorrection.

Unilateral abducens palsy with maximal abduction up to primary position should be treated by muscle transposition. With squint angles (far distance) < +20 degrees a classical Hummelsheim transposition is recommended, with squint angles > +20 degrees the Kaufmann's modification should be preferred. If abduction beyond primary position is possible, lateral rectus resection suffices. With squint angles > +12 degrees additional recession of the ipsilateral medial rectus muscle becomes necessary.