Horizontal effect of the surgical weakening of the oblique muscles

To evaluate the influence of the oblique muscles surgical weakening on the horizontal alignment in the primary position (PP) and its efficacy on the correction of the "A" and "V" anisotropies.

In order to study the influence of bilateral superior oblique muscles (SO) weakening on the horizontal alignment in PP, we analyzed the files of 12 patients who underwent only that operation; no other muscle was operated on. We took the opportunity of those 12 patients to analyze the effect of their operation on the correction of "A" incomitance. For evaluating the effect of the inferior oblique muscles (IO) weakening on the correction of the "V" pattern, we analyzed retrospectively the files of 67 anisotropic patients who underwent a bilateral SO weakening. In 10 of them, the only operation was the oblique muscles weakening and, in 57 patients, the horizontal recti were also operated on for the horizontal deviations in primary position. These patients were divided into two groups: 50 were esotropic and 17 exotropic. There was not any mixed anisotropy.

The mean value of the preoperative "V" incomitance of the 50 esotropic patients was 24.25∆ ± 10.15∆; the mean postoperative correction was 15.56 ∆ ± 8.74∆. The mean correction between the PP and upgaze was 7.52∆ ± 7.47∆ and from the PP to downgaze was 8.56∆ ± 9.21∆. The same values of the 17 exotropic patients was: preoperative 31.88∆ ± 9.4∆; primary position to upgaze was 13.11∆ ± 4.9∆ and primary position to downgaze 14.11∆ ± 12.48∆. The mean preoperative value of the "A" incomitance among the 12 patients who underwent isolated SO weakening was 30.50∆ ± 19.25∆ and the postoperative was of 9,92∆, therefore a mean correction of 22.58∆ ± 17.54∆. Among these ones, in 5 there was no alteration of the deviation in primary position, in 4 there was an exo-effect and in 3 there was an eso-effect. The mean alteration of the deviation in PP was an exo-shift of 2.25∆.

1) There was no difference in the relative correction of "V" pattern between the esotropic and exotropic patients, although the absolute numbers were greater in the exotropic ones. 2) The correction of the "V" pattern was between 65 and 75 % from the initial values. 3) The IO weakening corrected similarly the anisotropia between the superior and inferior components among the esotropic patients, but among the exotropic ones the correction was greater in the inferior component. 4) The SO weakening did not cause an eso-effect in the deviation in primary position.