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 inferior oblique muscle overaction (IOOA): 17 patients (male: 13 patients, female: 4 patients) underwent a unilateral 10-mm recession (10 mm-group) and 26 patients (male: 15 patients, female: 11 patients) underwent a standard 14-mm recession (14-mm group). The 10-mm inferior oblique recession was performed in patients with 2+ or less IOOA and the 14-mm inferior oblique recession in patients with greater than 2+ IOOA.6 The mean age of the 10- and 14-mm groups was 9.50 ± 10.8 years (range: 1.5 to 39 years) and 11.5 ± 12.2 years (range: 2.6 to 62 years), respectively, and there was no significant difference between the groups (P = .578).
At initial examination, the deviating angles in the primary position, right and left side gazes, up and down gazes, and right and left head tilting position were measured using alternate cover and prism testing. Unilateral excyclotorsion was identified and confirmed through fundus examination or fundus photography before the surgery. After the surgery, the deviating angles in primary position and contralateral gaze were measured at 1 and 3 months postoperatively. The effect of the recession was measured by preoperative hyperdeviation minus postoperative hyperdeviation at the postoperative times in both groups. Only the find-ings at 3 months were considered for statistical analysis.
The surgical technique was as follows. An inferotemporal conjunctival fornix incision was made and the conjunctiva and Tenon’s capsule were opened separately in layers. The inferior oblique muscle was identified and hooked under direct vision. The inferior oblique muscle was cleared of its surrounding inter-muscular septa from its insertion to near the temporal border of the inferior rectus muscle. A double-armed 6-0 polyglactin suture was then passed through the muscle adjacent to its insertion with lock-bites at either pole and the inferior oblique muscle was cut and disinserted near the insertion area. Following isolation and passage of inferior oblique sutures, posterior fibers of the inferior oblique muscles were bunched up using one single suture toward the main muscle belly to prevent spreading of posterior fiber.7 The two ends of the 6-0 polyglactin suture were then passed through scleral tunnels inserted 3 mm posteriorly and 2 mm lateral to the temporal pole of the inferior rectus muscle in the 10-mm group. In the 14-mm group, the anterior suture was inserted 10 mm posterior to the temporal pole of the inferior rectus muscle or straddled the exit site of the inferotemporal vortex vein from sclera.
Statistical analysis was performed using SPSS 12.0 for Windows (SPSS, Inc., Chicago, IL). The effect of both inferior oblique recessions was compared using the Mann–Whitney and Wilcoxon signed-rank tests. Statistical significance was defined as a P value of less than .05.
The average preoperative hyperdeviation was 13.4 ± 4.83 PD (range: 5 to 25 PD) in primary position and 16.2 ± 6.32 PD (range: 7 to 30 PD) in contralateral gaze in the 10-mm group and 8 ± 3.48 PD (range: 3 to 16 PD) in primary position and 12.76 ± 4.55 PD (range: 5 to 25 PD) in contralateral gaze in the 14-mm group (Table 1). Patients in the 10-mm group showed a broader range of preoperative hyperdeviation than those in the 14-mm group, and there was a statistically significant difference between the two groups in primary position. The average deviation at 3 months postoperatively in both groups was 2.1± 3.03 PD (range: 0 to 7 PD) in primary position and 2.6 ± 3.95 PD (range: 0 to 10 PD) in contralateral gaze in the 10-mm group and 0.8 ± 1.21 PD (range: 0 to 6 PD) in primary position and 1.8 ± 1.95 PD (range: 0 to 6 PD) in contralateral gaze in the 14-mm group. There was a statistically significant difference between the two groups postoperatively, but not concerning the deviation in contralateral gaze.
Table 1: Comparison of the Average Hyperdeviation Before and After Surgery
Also, the preoperative median units of inferior oblique overaction in the 14-mm group were larger than those in the 10-mm group, but there was no statistically significant difference between the two groups at 3 months postoperatively (Table 2). In the 10-mm group, the effect of surgery 3 months postoperatively ranged from 3 to 20 (median = 12 PD) in the primary position and 5 to 30 PD (median = 12 PD) in contralateral gaze (Table 3). In the 14-mm group, the effect of surgery at 3 months postoperatively ranged from 3 to 15 PD (median = 6 PD) in primary position and 4 to 24 PD (median = 12 PD) in contralateral gaze. Both groups showed a large range of self-grading effect in primary position and contralateral gaze 3 months postoperatively, but no statistically significant difference was evident between the two groups (P = .104 and .560, respectively; Mann–Whitney test).
Table 2: Comparison of the Median Units of Inferior Oblique Muscle Overaction Before and After Surgery
Table 3: Median and Ranges of the E3 ect of Both Inferior Oblique Recessions
Unilateral inferior oblique myectomy corrects 5 to 20 PD of hypertropia. Proponents of this surgery believe it is somewhat self-grading, in that greater effects are produced when the inferior oblique overaction is greater and lesser effects when overaction is less. Possible mechanisms for the self-grading effect can be that because an overactive inferior oblique muscle will be tight and, therefore, will contract more after disinsertion, reattaching posterior fibers farther from the original insertion will result in a less overactive (and presumably less tight) muscle.1 This could produce self-grading effect in inferior oblique myectomy. However, this is a hypothesis, which could be clearly investigated in future research with imaging studies.
Jampolsky8 reported that the inferior oblique muscle contributes practically nothing to elevation in the primary plane normally and it is only in abnormal conditions of marked overaction of the inferior oblique muscle, where the oblique muscle contracture acts in the primary position, that one can expect even a modest vertical correction in the primary position from inferior oblique muscle weakening. However, to date, inferior oblique recession and myectomy has shown a marked self-grading effect of up to 20 PD of vertical hypertropia in the primary position.
Both inferior oblique muscle recession procedures also had large self-grading effects in the current study. The range of self-adjusting effect at 3 months postoperatively was 3 to 20 PD in the primary position and 5 to 30 PD in contralateral gaze in the 10-mm group and 3 to 15 PD and 4 to 24 PD, respectively, in the 14-mm group. According to the hypothesis, this self-grading effect seemed to vary according to the extent of the reattachment site of posterior muscle fibers during the healing process.1
Shipman and Burke5 reported that inferior oblique myectomy and recession tended to produce a variable self-grading amount of correction of the hyperdeviation, even in the larger preoperative deviations, with inferior oblique myectomy resulting in the greatest reduction of the hyperdeviation and the most consistently favorable outcome. But they did not describe in detail the amount of self-grading effect of inferior oblique recession in the primary position. Unlike the previous report, the current study described the range of self-grading effect of inferior oblique recession for the first time. Although concurrent comparison of both procedures was not performed, the self-grading effect of inferior oblique recession was as large as that of myectomy in primary position and in contralateral gaze.
Although no statistically significant difference was evident between the two groups, the self-grading effect of inferior oblique recession in primary position and in contralateral gaze was larger in the 10-mm group than in the 14-mm group; however, the actual differences are rather small. Metten et al.2 suggested that large vertical deviations with small excyclodeviation are an indication for additional anteropositioning. Inferior oblique anterior transposition is the most powerful inferior oblique muscle-weakening procedure, with a correction of as much as 25 PD.9 Scott10 first described inferior oblique anteriorization, which involves the conversion of the vector of inferior oblique action from elevation to depression through the attachment of the inferior oblique muscle anterior to the equator. A 10-mm recession of the inferior oblique muscle also produces transposition of the inferior oblique muscle anterior to the equator.11,12 Therefore, it is reasonable to expect that inferior oblique surgery with attachment of the inferior oblique muscle anterior to the equator would be a larger self-grading operation because the posterior fiber of the inferior oblique muscle will be attached more variably in the healing process.
We divided the patients into two groups according to preoperative IOOA. As described by Parks,6 the recession operation is the most effective and long-lasting means of treating IOOA. The author suggested that, for a 1+, 2+, and 3+ overaction, the muscle be recessed by 6, 10, and 14 mm, respectively. In the current study, all patients were well corrected after the two procedures. Therefore, surgeons should select the type of inferior oblique surgery based on the degree of IOOA primarily because large self-titrating effects would ensue after both types of inferior oblique surgery.
This study had some limitations. First, the sample size of the study was small; therefore, the statistical power was weak. Second, the patient grouping was unevenly distributed because of its retrospective nature.
The current study determined that 10-mm and 14-mm inferior oblique muscle recession involves large self-grading effects in the primary position and in contralateral gaze.
- Rosenbaum AL, Santiago AP. Clinical Strabismus Management (Principles and Surgical Techniques). Philadelphia: W. B. Saunders; 1999;449–458.
- Metten M, Link H, Staubach F, Bach M, Lagrèze WA. Dose–response relationship in inferior oblique muscle recession. Graefes Arch Clin Exp Ophthalmol. 2008;246:593–598 doi:10.1007/s00417-007-0763-6 [CrossRef] .
- Davis G, McNeer KW, Spencer RF. Myectomy of the inferior oblique muscle. Arch Ophthalmol. 1986;104:855–858 doi:10.1001/archopht.1986.01050180089037 [CrossRef] .
- Toosi SH, von Noorden GK. Effect of isolated inferior oblique muscle myectomy in the management of superior oblique palsy. Am J Ophthalmol. 1979;88:602–608.
- Shipman T, Burke J. Unilateral inferior oblique muscle myectomy and recession in the treatment of inferior oblique muscle overaction: a longitudinal study. Eye (Lond). 2003;17:1013–1018 doi:10.1038/sj.eye.6700488 [CrossRef] .
- Parks MM. Inferior oblique weakening procedures. Int Ophthalmol Clin. 1985;25:107–117 doi:10.1097/00004397-198502540-00010 [CrossRef] .
- Elliott RL, Nankin SJ. Anterior transposition of the inferior oblique. J Pediatr Ophthalmol Strabismus. 1981;18:35–38.
- Jampolsky A. Superior rectus revisited. Trans Am Ophthalmol Soc. 1981;79:243–255.
- Kushner BJ. Restriction of elevation in abduction after inferior oblique anteriorization. J AAPOS. 1997;1:55–62 doi:10.1016/S1091-8531(97)90024-0 [CrossRef] .
- Scott AB. Planning inferior oblique muscle surgery. In: Reinecke RD, ed. Strabismus: Proceedings of the Third Meeting of the International Strabismological Association. New York: Grune and Stratton; 1978:347–354.
- Stein LA, Ellis FJ. Apparent contralateral inferior oblique muscle overaction after unilateral inferior oblique muscle weakening procedures. J AAPOS. 1997;1:2–7 doi:10.1016/S1091-8531(97)90016-1 [CrossRef] .
- Kim SH, Na JH, Cho YA. Inferior oblique transposition onto the equator: the role of the equator in development of contralateral inferior oblique overaction. J Pediatr Ophthalmol Strabismus. 2012;49:98–102 doi:10.3928/01913913-20110809-02 [CrossRef] .
Comparison of the Average Hyperdeviation Before and After Surgery
|Group||Preoperative (PD)||Postoperative 3 Months (PD)|
|Primary Position||Sursoadduction||Primary Position||Sursoadduction|
|10-mm recession (range)||13.4 ± 4.83 (5–25)||16.2 ± 6.32 (7–30)||2.1± 3.03 (0–7)||2.6 ± 3.95 (0–10)|
|14-mm recession (range)||8 ± 3.48 (3–16)||12.76 ± 4.55 (5–25)||0.8 ± 1.21 (0–6)||1.8 ± 1.95 (0–6)|
Comparison of the Median Units of Inferior Oblique Muscle Overaction Before and After Surgery
|Group||Preoperative||Postoperative 1 Month||Postoperative 3 Months|
|10-mm recession (range)||+2 (+1 to +2)||0 (−1 to 0)||0 (0)|
|14-mm recession (range)||+2.5 (+2 to +3)||0 (0 to +0.5)||0 (0 to +0.5)|
Median and Ranges of the E3 ect of Both Inferior Oblique Recessions
|Group||Primary Position (PD)||Sursoadduction (PD)|
|1 Month||3 Months||P||1 Month||3 Months||P|
|10-mm recession (range)||11 (3–20)||12 (3–20)||.202||12 (7–25)||12 (5–30)||.752|
|14-mm recession (range)||6 (3–16)||6 (3–15)||.715||10.5 (5–24)||12 (4–24)||.593|