We report two cases of strabismus on myotonic dystrophy treated with a surgical procedure.

A 49-year-old female with myotonic dystrophy presented with exotropia above 50 prism diopters and limitation of eye movement at nasal and inferior gaze in both eyes. We performed 9.25 mm lateral rectus recession in her right eye and 8.75 mm lateral rectus recession in her left eye. After surgery, she had 40 prism diopter residual exotropia. A 39-year-old female with myotonic dystrophy type 1 had outward deviation of her left eye. Prism cover-uncover test revealed 40 prism diopter exotropia at near distance and 25 prism diopter exotropia at far distance. We performed 6.0 mm lateral rectus recession and 4.5 mm medial rectus tucking in her left eye. Three months after surgery, the prism cover-uncover test showed 10 prism diopter residual intermittent exotropia at near distance and 6 prism diopter residual exophoria at far distance.

Not only cataract and retinal lesion, but also abnormal ocular movement and strabismus due to weakened extraocular muscles can occur in myotonic dystrophy patients. We recommend examination for functions of extraocular motility to diagnose and to treat for maintaining relatively straight alignment.