[Management of consecutive exotropia -- operative therapy and diplopia testing]

The aim of this study was to investigate the diagnostic value of preoperative sensory testing on postoperative diplopia and to evaluate the dose-effect relations of medial rectus muscle or unilateral recess/resect advancement procedures and their constancy.

A retrospective evaluation of 62 operative cases of consecutive exotropia performed from 2001 to 2003 was carried out. Diplopia after prismatic correction and after converging by minus glasses was tested. In 47 cases a unilateral recess/resect procedure and in 15 cases an advancement of the medial rectus muscle were performed. The postoperative results were controlled one week and three months after operation by measuring the angle of squint by a prism cover test looking in five metres and in 33 cm.

22 patients (36 %) had neither diplopia after prismatic correction of angle of squint nor after operation. The other 40 patients (64 %) experienced diplopia, but were not troubled by it. In all patients the whole amount of angle of squint was operated. Immediately after operation, 14 patients (23 %) experienced diplopia temporarily, which remained after 3 months in 9 patients, but all of them were not disturbed by it. In all patients the mean preoperative angle of - 19 degrees was corrected by a mean operative amount of 11 mm, the mean postoperative angles were + 1.5 degrees after one week and - 2.6 degrees after three months with considerable variations of the results (standard deviations were about 5 degrees ). In 15 cases with advancement of the medial rectus muscle the dose-effect relation was 2 degrees per mm operative amount. After three months these patients become more divergent, the mean value was - 6 degrees , the dose-effect relation was reduced to 1.4 degrees /mm. The unilateral recess/resect operations were more constant: these became more divergent of 2.5 degrees only and their dose-effect relation remained more constant (after one week: 1.9 degrees /mm, after 3 months: 1.7 degrees /mm).

The diagnostic value of preoperative prismatic correction of the deviation is very limited. Even if diplopia can be provoked, the chance of disturbing diplopia is very low. Nevertheless, some guidelines for pre- and postoperative care are necessary to prevent double vision. The postoperative outcome is favourable for the patient after one operation. In cases of relapsing divergence a second operation is easily possible.