The effect of anterior transposition of the inferior oblique muscle on the palpebral fissure.

BACKGROUND Anterior transposition of the inferior oblique muscle is a popular treatment for dissociated vertical divergence. It seems that this surgical procedure may alter the palpebral fissure. OBJECTIVES To investigate the alteration of the palpebral fissure with inferior oblique muscle anterior transposition when it is performed as the sole operative procedure and to report the cases of patients who developed noticeable upper eyelid retraction after inferior oblique muscle anterior transposition preceded by large superior rectus muscle recessions. METHODS The change in the height of the palpebral fissure surgery was evaluated from photographs by 2 masked observers in 3 groups of patients. The control group underwent inferior oblique muscle recession without transposition. The second group (or the insertion study group) underwent transposition of the inferior oblique muscle that was level with the inferior rectus muscle insertion. The third group (or the 2-mm study group) had the inferior oblique muscle placed 2 mm anterior to the inferior rectus muscle insertion. Also, the insertion study and the control groups were evaluated after surgery for bulging and elevation of the lower eyelid on upgaze. RESULTS The narrowing of the palpebral fissure after surgery (mean + SD) was -0.14 + 0.6 mm in the 16 patients in the control group, -1.2 + 0.9 mm in the 14 patient in the insertion study group, and -2.1 + 0.5 mm in the 6 patients in the 2-mm study group. The differences were statistically significant between the control and the insertion study groups (P= .001, t test) and between the control and the 2-mm study groups (P< .001, t test). One of the 16 control patients and 10 of the 14 insertion study patients showed bulging of the lower eyelid on upgaze after surgery. This difference was statistically significant (P<.001, Fisher exact test). In addition, 3 patients were seen who developed marked upper eyelid retraction when anterior transposition of the inferior oblique muscles followed previous large superior rectus muscle recessions. CONCLUSIONS Anterior transposition of the inferior oblique muscle causes significant narrowing of the palpebral fissure as a sole procedure. When preceded by large superior rectus muscle recessions, it can cause upper eyelid retraction. Arch Ophthalmol. 2000;118:1542-1546