Muscle Weakening and Change of Tension According to Degree of Superior Rectus Z-Myotomy in Rabbits

PURPOSE: To identify the muscle weakening effect and the change of muscle tension according to degree of superior rectus Z-myotomy in rabbits. METHODS: After dissection of superior rectus in 15 rabbits (30 eyes), marking was done on 10 mm apart from muscle insertion. Then, Z-myotomy was done on 2 mm and 8 mm apart from muscle insertion which are two different positions on apposite sides. 25%, 50% and 75% Z-myotomy were defined as group 1 (10 eyes), group 2 (10 eyes) and group 3 (10 eyes). After Z-myotomy, the change of muscle lengthening between muscle insertion and marking, and muscle tension were measured. At 4 weeks after Z-myotomy, all parameters were re-measured. RESULTS: After Z-myotomy all markings moved posteriorly, and showed result as 10.83 +/- 0.13 mm in group 1, 11.02 +/- 0.17 mm in group 2 and 12.01 +/- 0.23 mm in group 3 respectively. Muscle tension result showed as 3.98 +/- 0.22 mm in group 1, 3.54 +/- 0.18 mm in group 2 and 2.87 +/- 0.25 mm in group 3. In comparison of three groups, group 2 and group 3 showed the significant results (p < 0.05). At 4 weeks after Z-myotomy the markings showed result as 10.55 +/- 0.14 mm, 10.85 +/- 0.20 mm, 11.91 +/- 0.14 mm respectively, and in group 2 and group 3 the significant changes were seen (p < 0.05). Muscle tensions were 4.01 +/- 0.31 mm, 3.88 +/- 0.53 mm, 3.12 +/- 0.42 mm respectively. There were significant results in group 2 and group 3 (p < 0.05). CONCLUSIONS: 75% Z-myotomy of superior rectus showed significant results in muscle weakening and decreasing muscle tension.

Muscle Weakening Effect After Superior Rectus Z-myotomy in Rabbits

PURPOSE: To experimentally investigate the effect for muscle weakness after superior rectus Z-myotomy and histological changes. METHODS: Superior rectus muscle fibers of rabbits (16 rabbits, 32 eyes) were cut transversely with scissors across 75% of the muscle in two different positions on opposite sides. In group 1 (16 eyes), myotomies were performed at 2 and 7 mm from the muscle insertion (5 mm gap) and in group 2, performed at 2 and 5 mm (3 mm gap). The change of mark, eyeball position, and muscle tension after myotomy and 4 weeks postoperatively was evaluated, the location of the mark was examined, and muscle tissue biopsy was performed. RESULTS: After Z-myotomy, the marks of the two groups moved significantly posteriorly from insertion within groups (p<0.05), with no significant differences between groups (p=0.469). Eyeball positions of the two groups moved significantly inferiorly (p<0.05); the amount of position change of group 1 was greater than group 2 (p<0.05). When the globe was pulled in opposite directions for muscle action, the degree of change decreased with significant difference within groups (p<0.05), but there were no significant differences between groups (p=0.32). CONCLUSIONS: Z-myotomy of the superior rectus muscle affected the recession of eyeball position and weakened the muscle action. Muscle weakening affected by the different gaps between myotomies did not show consistent results.

Inferior oblique overaction

Inferior oblique myectomies or Z-myotomies were performed on 159 eyes of 121 patients who had an overacting inferior oblique muscle or muscles. The results were as follows; 1. Success rates were 95.5% in myectomy and 71.4% in Z-myotorny. 2. Recurrence rates were 2.7% in myectomy and 14.3% in Z-myotomy. 3. There were no other complications to include the adherence syndrome.