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Introduction
Superior oblique palsy is the most common form of isolated vertical muscle palsy. Weakening the antagonist inferior oblique muscle is commonly used to treat superior oblique palsy when there is an overaction of the inferior oblique muscle. This can be accomplished by an inferior oblique myectomy, recession, disinsertion or extirpation, or recession with anterior transposition. 1 Among these methods, the most commonly performed inferior oblique muscle-weakening procedures are inferior oblique myectomy and inferior oblique recession. The decision on the surgery types appears to be primarily based on individual experience and preference.
In contrast to rectus muscle surgery, for which well-defined dosage guidelines exist, a systematically established dose--response relationship for operations on oblique muscles is rare. Metten et al.2 reported that the vertical dose--response was 1 to 1.2 prism diopters (PD) per millimeter in primary gaze and 2.2 to 2.4 PD per millimeter in adduction. However, they pointed out that the variance was high, and large vertical deviations with small excyclodeviation are an indication for additional anteropositioning.
It is well known that the amount of vertical correction is roughly proportional to the degree of preoperative overaction.3--5 This phenomenon was termed the "self-grading effect"3,5 or "self-adjusting effect."4 Davis et al.3 reported that inferior oblique myectomy has a self-grading effect ranging from 5 to 20 PD.3 However, there has been no report describing the amount of self-grading effect of inferior oblique recession.
The aim of our study was to estimate the ranges of effect of inferior oblique recession in primary position and contralateral gaze (gaze to the non-paretic eye) between 10- and 14-mm recession, and to clarify the extent of the self-grading effect (ie, the effect of the recession dependent on the preoperative hyperdeviation) of the inferior oblique recession.
Patients and Methods
The records of 43 patients who underwent an inferior oblique recession for congenital unilateral superior oblique palsy were retrospectively reviewed. The study followed the tenets of the Declaration of Helsinki and was approved by the institutional review board at Korea University Medical Center. No patient had previously undergone any muscle surgery and no other surgery was performed at the same time as the inferior oblique muscle-weakening procedure.
Patients were divided into two groups according to the degree of...