Dose-Effect Relationship of Unilateral Medial Rectus Resection for Recurrent Exotropia

PURPOSE: To investigate the dose-effect relationship of unilateral medial rectus resection for recurrent exotropia after bilateral lateral rectus recession. METHODS: This study comprised 39 patients who underwent unilateral medial rectus resection for recurrent exotropia under 25 PD and bilateral rectus recession for prior surgery of exotropia. The medial rectus was resected from 5.0 to 7.0 mm according to angle deviation at a distance. The postoperative deviated angle was checked at one week, 3 months and 6 months postoperatively to investigate the amount of corrected deviation per resected muscle. RESULTS: The average preoperative deviation was 21.33 +/- 2.96 PD. We resected mean 6.26 +/- 0.57 mm of the medial rectus muscle. The postoperative deviated angle was 0.82 +/- 3.47, 1.87 +/- 3.10 and 5.40 +/- 4.79 PD at 1 week, 3 months and 6 months after surgery, respectively. The corrected deviated angle per millimeter (mm) was 3.29 +/- 0.68, 3.17 +/- 0.58 and 2.75 +/- 0.89 PD at 1 week, 3 months and 6 months after surgery. There were no significant differences among the changes of postoperative deviation per millimeter according to the amount of medial rectus (MR) resection (p-value = 0.423, 0.382) The success rate was 89.75%, 92.31% and 87.18% at 1 week, 3 months and 6 months after surgery, respectively. The expected corrected angle according to the amount of resection remained constant and was 3.04-3.22 PD/mm at 3 months after surgery and 2.79-2.82 PD/mm at 6 months after surgery. CONCLUSIONS: The dose-effect per millimeter was decreased as time passed. There was no statistical difference among the corrected deviation angles per millimeter according to the amount of MR resection. We expect that the calculated dose-effect relationship may be a useful guideline for unilateral medial rectus resection for recurrent exotropia.

Change of Strabismus Angle and Deviation After Unilateral or Bilateral Lateral Rectus Recession in Exotropia

PURPOSE: To compare the changes in strabismus angle and deviation between two groups: a bilateral lateral rectus recession (Group 1) and a unilateral lateral rectus recession in exotropia (Group 2). METHODS: A retrospective survey was conducted on 198 patients who had received exotropia surgery in our ophthalmology clinic from September 2003 to April 2007. A total of 116 patients were in Group 1, and 82 patients were in Group 2. RESULTS: The average deviations of the first postoperative month and the first postoperative year were -1.96 D +/- 4.75, 2.5 D +/- 7.82 for Group 1 and 0.77 D +/- 2.87, 5.94 D +/- 3.38 for Group 2. Revealing statistical significance between the 2 Groups: Group 1 had 30 failure cases (25.9%) and their 1 postoperative year average deviation was 5.42 D +/- 13.97, while Group 2 showed 24 failure cases (29.3%) and their 1-postoperative-year average deviation was 13.0-79 +/- 3.04. Group 1 had less strabismus angle and a greater standard deviation than Group 2, as Group 1 had more overcorrection. Among the 30 failure cases of Group 1, 9 were overcorrected and 21 were undercorrected, but all 24 failure cases in Group 2 were undercorrected. CONCLUSIONS: The strabismus angle after lateral rectus recession showed a wider variation and a larger difference in bilateral lateral rectus recession than in the unilateral lateral rectus recession.

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.

The Effect of Medial Rectus Resection in Reccurent Exotropia After Lateral Rectus Recession

PURPOSE: To investigate the effect of unilateral medial rectus resection in recurrent exotropia under 25 Prism Diopter after unilateral or bilateral lateral rectus recession. METHODS: A retrospective chart analysis was conducted for 21 patients who underwent unilateral medial rectus resection for recurrent exotropia under 25PD and uni- or bilateral lateral rectus recession for prior surgery of exotropia. The medial rectus was resected from 5.0 to 7.0 mm by 0.5 mm according to angle deviation at a distance. The postoperative deviated angle was checked at one week, three months and six months postoperatively to investigate the amount of corrected deviation per resected muscle. RESULTS: The average preoperative deviation was 20.57+/-3.37PD. We resected mean 6.1+/-0.62 mm of the medial rectus. At one week after the surgery, the postoperative deviated angle was 2.00+/-4.32PD, After six months it was 6.57+/-7.40PD, and there appeared to be an increase of deviation. Ten patients (48%) fused before surgery and 12 (57%) after surgery. The corrected deviation per resected muscle was 2.88+/-1.08PD. CONCLUSIONS: Unilateral medial rectus resection is an effective surgical method for the treatment of recurrent exotropia under 25 PD after lateral rectus recession.

The inhibitory Effects of Mitomycin-C on the Development of Proliferative Vitreoretinopathy

PURPOSE: To investigate the inhibitory effect of MMC on experimental PVR. METHODS: The cultured rabbit fibroblasts were pretreated with 3microgram/L and 300microgram/L concentration of MMC for 30 minutes. MMC-treated and -untreated fibroblasts were injected into vitreous cavity of pigmented rabbits and the development of PVR was compared each other. The retinal toxicity of MMC was evaluated histopathologically after 30 minutes-intravitreal infusion with the same concentration of MMC. RESULTS: On the final examination 8 weeks after intravitreal injection, the rate of PVR was 90%, 67%, and 20% in control group without MMC treatment, 3.0 microgram/L MMC-treated group, and 300 microgram/L MMC-treated group, respectively. The severity of PVR was milder in treatment groups than in non-treatment group in general, and the rate of PVR between control group and 300 microgram/L MMC-treated group was statistically significant (P<0.01). At 1 and 4 weeks of histopathologic study using the light and electromicroscopy to evaluate the retinal toxicity to MMC, the retina and retinal pigment epithelium showed similar findings in MMC-treated groups compared to non-MMC-treated control group. CONCLUSIONS: These results show that pharmacologic therapy with MMC may be useful in the prevention of development and recurrence of PVR in the management of complex retinal detachment.