Contemplation of the surgical normogram of lateral rectus recession for exotropia associated with superior oblique palsy.

PURPOSE: To suggest a surgical normogram for lateral rectus recession in exotropia associated with unilateral or bilateral superior oblique muscle palsy (SOP). METHODS: We retrospectively reviewed the charts of 71 patients with exotropia who were successfully corrected over one year. Each patient had undergone unilateral or bilateral rectus recession associated with uni- or bilateral inferior oblique (IO) 14 mm recession, using a modified surgical normogram for lateral rectus (LR) recession, which resulted in 1 to 2 mm of reduction of LR recession. We divided all patients into 2 groups, the 34 patients who had undergone LR recession with unilateral IO (UIO) recession group and the remaining 37 patients who had undergone LR recession with bilateral IO (BIO) recession group. Lateral incomitancy was defined when the exoangle was reduced by more than 20% compared to the primary gaze angle. The surgical effects (prism diopters [PD]/mm) of LR recession were compared between the two groups using the previous surgical normogram as a reference (Parks' normogram). RESULTS: The mean preoperative exodeviation was 20.4 PD in the UIO group and 26.4 PD in the BIO group. The recession amount of the lateral rectus muscle ranged from 4 to 8.5 mm in the UIO group and 5 to 9 mm in the BIO group. Lateral incomitancy was noted as 36.4% and 70.3% in both groups, respectively (p = 0.02). The effect of LR recession was 3.23 ± 0.84 PD/mm in the UIO group and 2.98 ± 0.62 PD/mm in the BIO group and there was no statistically significant difference between two the groups (p = 0.15). CONCLUSIONS: Reduction of the LR recession by about 1 to 2 mm was successful and safe to prevent overcorrection when using on IO weakening procedure, irrespective of the laterality of SOP.

Ultrastructural study of extraocular muscle tendon axonal profiles in infantile and intermittent exotropia.

PURPOSE: To investigate the ultrastructures of tendon axonal profiles in infantile and intermittent exotropia. Tendon axonal profiles are composed of myotendinous nerve endings that are presumed to serve as sensorial receptors in ocular proprioception. METHODS: The study subjects included 10 patients with exotropia who had undergone surgery in one eye (recession and resection). They were divided into two equal groups. Five patients with infantile exotropia that had developed at under 12 months of age were allocated to group A. Another five, with intermittent exotropia that had developed at over 12 months of age, were allocated to group B. In all patients, medial recti were resected by 3-4 mm in order to obtain tissue samples, which were then examined under an electron microscope. RESULTS: In group A, we noted many axonal degenerative findings, such as the retraction of axons from myelin sheaths with considerable shrinkage, axonal disintegration, and Schwann cell proliferation. On the other hand, we identified three unique findings in group B: intact axons with incomplete Schwann cell wrapping; intact Schwann cells not associated with axons, and disorganized Schwann cells with shrunken axons. CONCLUSION: Different patterns of tendon axonal profiles were seen in association with the two types of exotropia. These differences may be related to the pathogenesis of these exotropia types.