The effect-of anterior transposition of the inferior oblique muscle on thepalpebral fissure

Background: Anterior transposition of the inferior oblique muscle is a popu lar treatment for dissociated vertical divergence. It seems that this surgi cal procedure may alter the palpebral fissure. Objectives: To investigate the alteration of the palpebral fissure with inf erior oblique muscle anterior transposition when it is performed as the sol e operative procedure and to report the cases of patients who developed not iceable upper eyelid retraction after inferior oblique muscle anterior tran sposition preceded by large superior rectus muscle recessions. Methods: The change in the height of the palpebral fissure surgery was eval uated from photographs by 2 masked observers in 3 groups of patients. The c ontrol, group underwent inferior oblique muscle recession without transposi tion. The second group (or the insertion study group) underwent transpositi on of the inferior oblique muscle that was level with the inferior rectus m uscle insertion. The third group (or the 2-mm study group) had the inferior oblique muscle placed 2 mm anterior to the inferior rectus muscle insertio n. Also, the insertion study and the control groups were evaluated after su rgery for bulging and elevation of the lower eyelid on upgaze. Results: The narrowing of the palpebral fissure after surgery (mean+/-SD) w as -0.14+/-0.4 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 pa tients in the 2-mm study group. The differences were statistically signific ant 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 bulgi ng of the lower eyelid on upgaze after surgery. This difference was statist ically significant (P<.001, Fisher exact test). In addition, 3 patients wer e seen who developed marked upper eyelid retraction when anterior transposi tion of the inferior oblique muscles followed previous large superior rectu s muscle recessions. Conclusions: Anterior transposition of the inferior oblique muscle causes s ignificant narrowing of the palpebral fissure as a sole procedure. When pre ceded by large superior rectus muscle recessions, it can cause upper eyelid retraction.