gms | German Medical Science

Large convergent squint angles can occur after three wall orbital decompression in patients with thyroid associated ophthalmopathy (TAO) and compressive optic neuropathy. These squint angles can be too large to be corrected by a simple recession of the medial rectus muscle. Resection of the lateral rectus muscle is not recommendable, because the medial rectus muscles are trapped in the ethmoid cells. I new operating procedure will be introduced.

Large convergent squint angles have been corrected in 14 patients with a medial rectus muscle tendon elongation with a 8 mm wide Tutoplast^® interponate. The length was preoperatively determined. The interponate was fixated with two Ethibond^® 6.0 stitches at the muscle tendon and at the original muscle insertion (8 cases) or 3 mm behind (6 cases). Monocular excursions and squint angles in primary position were evaluated preoperatively and 3 and about 7 months after the operation.

The median preoperative squint angle in primary position was +27° (max: 40°; min 10°). Seven months postoperatively the median preoperative squint angle was 0° (max: 0°; min +10°). 10 of 14 patients had no double vision in primary position postoperatively (far fixation). The dose effect coefficient (improvement of the squint angle [°]/amount of recession (R) of the muscle [mm]) was lower for the tendon elongation (1.1°/mm R) in comparison to a bilateral medial rectus recession (1.58°/mm R) in patients without prior orbital decompression. The standard deviation was low (0.2°/mm R) (max: 1.6; min 0.9). Abduction improved on average about 13.4° (±0.6°) to 22.3° and adduction deteriorated on average about 15.6° (±6.4°) to 16.2°. The resulting convergence deficit exceeded in no case more than -5° (median -1.9°). The fixation of the interponate 3 mm behind the original insertion of medial rectus muscle resulted in better conjunctival appearance.

The results of the trial revealed that medial rectus muscle tendon elongation with a Tutoplast^® interponate is a safe method to correct large convergent squint angles after orbital decompression. The low dose effect coefficient might be a result of the tendon fixation close to the original insertion which preserves normal leverage due to normal arc of contact. A significant convergence insufficiency did not occur.