The purpose of the current study was to evaluate the efficacy of a new surgical technique in reducing inferior oblique muscle overaction. Horizontal strabismus can be associated with either primary (commonly associated with horizontal strabismus) or secondary (ipsilateral superior oblique palsy-related) inferior oblique overaction. Anterior transposition and myectomy of the inferior oblique muscle are also used in the treatment of dissociated vertical deviation, including cases in which a simultaneous inferior oblique muscle overaction is also present.1–3 The surgical technique we experimented with can be used in all cases in which inferior oblique overaction is associated with elevation in adduction, superior oblique palsy, and V-pattern exotropia or esotropia. The surgical procedure consists of suturing the muscle to the sclera at the Gobin point with tendon sparing and also using a micro-incision to minimize the related tissue trauma and induce faster recovery.
Patients and Methods
Eight patients between the ages of 5 and 51 years (mean: 25.6 years) with inferior oblique muscle overaction were selected to undergo the surgical procedure. In one case, the unilateral inferior oblique overaction induced an 18-prism diopters (PD) vertical deviation. In 2 patients, the elevation in adduction was related to essential infant esotropia. Five patients had V-pattern exotropia between 15 and 40 PD (mean preoperative deviation: 27 PD). All patients underwent a strabismus procedure consisting of the suturing of the entire body of the muscle at the sclera in correspondence to the Gobin point (anteroposition of the inferior oblique muscle with the bulbar insertion to the equator)4 using a non-absorbable 5-0 GORE-TEX suture (W. L. Gore & Associates, Flagstaff, AZ) with tendon sparing.
No selection bias was used. All of the procedures were performed by the same surgeon between March and October 2012. Five cases were performed under local anesthesia and the remaining three had general anesthesia. In three cases, the surgery was performed through a micro-incision. Exclusion criteria included previous strabismus surgery or combined surgery on another vertical muscle at the same surgical time (previous horizontal rectus muscle surgery preceding the inferior oblique surgical procedure was not considered an exclusion criterion).
Age, amount of surgery, etiology, visual acuity, and motor alignment were assessed using the cover/uncover test. Alternate prism cover testing at distance (20 ft) and near (14 in) in the cardinal gaze position, versions, stereoacuity (Titmus fly test), and torsions (double Maddox rods) were collected preoperatively and 1 day and 4 months after surgery. One of the 2 eyes was patched for 30 minutes and alignment was then reexamined due to the small deviation in primary gaze. The primary outcomes were reduction of lateral incomitance after surgery and the number of postoperative overcorrections (defined as any kind of deviation opposite the original). Any residual hypertropia was considered an under-correction.
Four months after surgery, the mean angle of deviation was reduced to 8 PD exotropia in the group of 5 patients with V-pattern esotropia; the patient with unilateral inferior oblique overaction had the vertical deviation reduced to 3 PD. Finally, 2 patients with essential infant esotropia had a complete resolution of the elevation in adduction with no residual vertical imbalance. All patients experienced an improvement in lateral incomitance. The new technique was also performed through a micro-incision that appeared easier and faster.
Many studies have evaluated the effectiveness of inferior oblique surgery in hypertropias and inferior oblique recession has been a well-accepted surgical procedure in patients with superior oblique palsy manifesting over elevation in adduction.5 Recession of the inferior oblique muscle was indicated by Parks as the most effective and longest lasting procedure for inferior oblique weakening.6 However, in the 1970s, anatomical studies introduced new tables for graded muscle recession (8- to 10-mm inferior oblique recession corrects 9- to 15-prism diopters central gaze hypertropia).7 Metten et al. published a new dose-response study, having performed inferior oblique recession procedures of 0.5°/mm to 1.4°/mm.8 Because of its anatomical position, the inferior oblique muscle works as an extorter and elevator muscle to make recession with anterior Gobin’s position procedure effective in reducing inferior oblique overaction.
It was necessary that all posterior body fibers were fully hooked. To increase the depression, it was also necessary to suture closer to the inferior rectus muscle. Inserting the equator near the lateral rectus muscle increased the abduction with good action of depression. If the inferior oblique muscle is wrongly transposed in a slightly more advanced position with respect to the equator and closer to the inferior rectus muscle insertion, it will start working as an intortion tonic depressor muscle with a resulting “anti-elevation syndrome.” To further increase the strength of the depression, it is possible to apply the muscle GORE-TEX suture further away from the scleral insertion of the inferior oblique muscle in correspondence to the sclera beyond the equator line; this can increase the risk of anti-elevation syndrome.
The new technique we used, “equatorial scleral anchor,” consists of suturing the inferior oblique muscle belly directly to the sclera at the Gobin point without removing its own anatomical insertion. The obtained inferior oblique muscle weakening is due to two different mechanisms: anchor at the Gobin point (recession-shifted-forward procedure) and reduction of the total muscle length. The inferior oblique muscle measured 37 mm from the tear crest of the maxillary bone at its insertion on the inferior-lateral quadrant of the sclera into the rear hemisphere. Thanks to our surgical technique, the muscle is working actively on the Gobin point. If we consider that the portion between the scleral point (Gobin point) and the insertion point is 11 mm (R = 11 mm), then the final muscle active portion is 26 mm (37 – 11 mm = 26 mm). On the contrary, the final muscle active portion obtained with the normal recession-shifted-forward procedure is the whole muscle (37 mm). The equatorial scleral anchor produces the same anatomical result of an 11-mm inferior oblique muscle resection with the benefit of not having the muscle cut and with considerably greater income if compared with the well-known recession-shifted-forward procedure.
The equatorial scleral anchor procedure can be performed through micro-incision, minimizing related tissue trauma, inducing a faster recovery, and reducing the risks of a postoperative adherence syndrome. The classic inferior oblique anterior transposition technique provides a similar outcome. However, the new technique offers the advantages of being simple, safe, reversible, and modular in terms of suturing. Even if the technique could still be improved and refined (absorbable vs non-absorbable sutures), it offers additional benefits such as no or minimal risk to developing vorticose hemorrhage or macular damage, no errors in inferior oblique muscle hooking with the lateral rectus muscle, and no risk of anti-elevation syndrome. These features make this technique a valid alternative to the standard classic procedures.
- Bacal DA, Nelson LB. Anterior transposition of the inferior oblique muscle for both dissociated vertical deviation and/or inferior oblique overaction. Binocular Vision Eye Muscle A. 1992;7:219–225.
- Kratz RE, Rogers GL, Bremer DL, Leguire LE. Anterior tendon displacement of the inferior oblique for DVD. J Pediatr Ophthalmol Strabismus. 1989;26:212–217.
- Pineles SL, Velez G, Velez FG. Asymmetric inferior oblique transposition for incomitant asymmetric dissociated vertical deviation. Graefes Arch Clin Exp Ophthalmol. 2013;251:2639–2642. doi:10.1007/s00417-013-2445-x [CrossRef]
- Gobin MH. Anteroposition of the inferior oblique muscle in V-esotropia. Ophtalmologica. 1965;149:138–141. doi:10.1159/000304744 [CrossRef]
- Simons BD, Saunders TG, Siatkowsky RM, et al. Outcome of surgical management of superior oblique palsy: a study of 123 cases. Binocul Vis Strabismus Q. 1998;13:273–282.
- Parks MM. The weakening surgical procedure for eliminating overaction of the inferior oblique muscle. Am J Ophthalmol. 1972;73:107–122. doi:10.1016/0002-9394(72)90313-3 [CrossRef]
- Apt L, Call NB. Inferior oblique muscle recession. Am J Ophthalmol. 1978;85:95–100. doi:10.1016/S0002-9394(14)76672-3 [CrossRef]
- 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]