Vertical transposition of medial rectus muscles for correction of A-pattern anisotropia

A-pattern esotropias without superior oblique muscle overaction form a small but distinct group among A and V pattern anisotropias. The purpose of this study was to determine the results of ungraded 5 mm bilateral medial rectus muscle transpositions as a treatment of A anisotropia in esotropic patients, and to study these results with relation to the magnitude of preoperative A anisotropia and to the magnitude of preoperative esotropia in primary position.

Patient data on all 37 esotropic patients who had 5 mm elevation of the medial rectus muscle insertion for correction of A anisotropia at our institution during the previous 25 years were studied. We considered the surgical result to be "satisfactory" when a total correction, and A pattern less than 10 Prism Diopters (PD) or a V pattern less than 15 PD were obtained. The patients were divided into different groups, according to the magnitude of the preoperative A pattern and according to the magnitude of the preoperative esotropia in primary position. For statistical analysis, the Chi Square and the Fisher Tests were employed.

"Satisfactory" results were found in 70.3% of the cases. The mean correction of A anisotropia was 11.4 PD (76.1%), which corresponded to 2.3 PD per millimeter of transposition. "Unsatisfactory" results were more prevalent in patients with esotropia in primary position larger than 40 PD (p=0.0418).

A five millimeter vertical transposition (elevation) of both medial rectus muscles is an effective treatment for correction of A anisotropia in most esotropic patients, but is associated with unsatisfactory results when the preoperative esotropia in primary position is larger than 40 PD.