To define the clinical characteristics of acute vertical strabismus in adults strabismus without known ocular and cranial external factors.

We performed a retrospective study of 72 adult patients who developed acute vertical strabismus without known ocular and cranial external factors such as trauma or operation and were followed up for at least 6 months.

Undetermined cause (n = 41, 57%) was the most common etiology of acute vertical strabismus, followed by fourth cranial nerve palsy (n = 15, 20.8%), myasthenia gravis (n = 7, 9.7%), third cranial nerve palsy (n = 6, 8.3%), brain tumor (n = 2, 2.7%), and carotid-cavernous fistula (n = 1, 1.3%). The average vertical deviation at primary position was 7.2 prism diopter at initial visit. Thirty-eight (62.3%) patients recovered to orthophoria and 13 (21.3%) patients showed decreased level of diplopia. The average recovery period was 2.9 months. Ten cases remained as strabismus and 5 underwent surgery upon patient's request.

Unknown cause was the most common diagonosis of adult acute vertical strabismus without known ocular and cranial external factors. In the present study, 62.3% of patients recovered to orthophoria and 83.6% recovered without surgical procedures.