Magnetic resonance imaging measurements of extraocular muscle path shift and posterior eyeball prolapse from the muscle cone in acquired esotropia with high myopia.

PURPOSE: To investigate extraocular muscle (EOM) path shift and prolapse of posterior eyeball from muscle cone in acquired esotropia with high myopia (AEHM), using magnetic resonance imaging.

DESIGN: A case-control study.

METHODS: There were 16 eyes with AEHM, 11 with high myopia (HM), 12 with moderate myopia (MM), and 11 control eyes. Extraocular muscle shift was evaluated by measuring angles formed by the line connecting orbital centroids and the line connecting each orbital centroid and each EOM centroid. The ratio of the prolapse in the posterior eyeball from the muscle cone was also measured.

RESULTS: Both inferior shift of lateral rectus (LR) and nasal shift of superior rectus (SR) muscle were observed in the AEHM group, compared with HM, MM, and control groups. Neither shifted significantly in the HM group compared with control group. The prolapse ratio in AEHM group was higher than in the HM, MM, and control groups. Greater EOM shifts and eyeball prolapse were observed when the AEHM was more severe, as in esotropia fixus.

CONCLUSIONS: In AEHM, a prolapsing eyeball shifts LR inferiorly and SR nasally; these findings were not observed in high myopia with neither ocular deviation nor restriction. These shifts reduce abduction and supraduction and increase infraduction and adduction in AEHM. The shifts would be predicted to create a hypoesodeviation, which is a common finding in AEHM. Both EOM shifts and superotemporal eyeball prolapse tend to be greater in esotropia fixus.