Temporal Slant Recession of the Inferior Rectus Muscle: A Simple Surgical Treatment for Diplopia Caused by Small Vertical Deviations

Background: To evaluate the therapeutic effect of temporal slant recession of the inferior rectus muscle (TSRIRM) for the treatment of small vertical deviations in patients with vertical diplopia, with consideration of the theoretical additive effects of this procedure on ocular torsion and horizontal incomitance. Methods: Retrospective review of 11 patients who were treated with TSRIRM. Eight patients with vertical diplopia and small hyperdeviations (up to 6 prism diopters (PDs)) were treated with isolated TSRIRMs. Three patients with vertical diplopia from unilateral superior oblique palsies with large hyperdeviations (>15 PDs) were treated with TSRIRMs in conjunction with contralateral inferior oblique recessions. Results: Six of the 8 patients with small vertical deviations had successful vertical realignment with elimination of symptomatic diplopia after an isolated TSRIRM. Two of the eight patients had residual hypertropia with symptomatic diplopia. Three additional patients with unilateral superior oblique palsy had successful vertical realignment with elimination of symptomatic diplopia after ipsilateral inferior oblique recession and contralateral TSRIRM. In total, 9 of 11 patients had successful surgical results after TSRIRM. Conclusions: TSRIRM provides an effective and reliable treatment for small angle vertical strabismus. Its ease of surgical access renders it useful for implementation in an outpatient neuro-ophthalmology setting.

Original Contribution Section Editors: Clare Fraser, MD Susan Mollan, MD Temporal Slant Recession of the Inferior Rectus Muscle: A Simple Surgical Treatment for Diplopia Caused by Small Vertical Deviations Michael C. Brodsky, MD Background: To evaluate the therapeutic effect of temporal slant recession of the inferior rectus muscle (TSRIRM) for the treatment of small vertical deviations in patients with vertical diplopia, with consideration of the theoretical additive effects of this procedure on ocular torsion and horizontal incomitance. Methods: Retrospective review of 11 patients who were treated with TSRIRM. Eight patients with vertical diplopia and small hyperdeviations (up to 6 prism diopters (PDs)) were treated with isolated TSRIRMs. Three patients with vertical diplopia from unilateral superior oblique palsies with large hyperdeviations (.15 PDs) were treated with TSRIRMs in conjunction with contralateral inferior oblique recessions. Results: Six of the 8 patients with small vertical deviations had successful vertical realignment with elimination of symptomatic diplopia after an isolated TSRIRM. Two of the eight patients had residual hypertropia with symptomatic diplopia. Three additional patients with unilateral superior oblique palsy had successful vertical realignment with elimination of symptomatic diplopia after ipsilateral inferior oblique recession and contralateral TSRIRM. In total, 9 of 11 patients had successful surgical results after TSRIRM. Conclusions: TSRIRM provides an effective and reliable treatment for small angle vertical strabismus. Its ease of surgical access renders it useful for implementation in an outpatient neuro-ophthalmology setting. Journal of Neuro-Ophthalmology 2023;43:406–409 doi: 10.1097/WNO.0000000000001677 © 2022 by North American Neuro-Ophthalmology Society S mall vertical deviations are a common cause of troublesome diplopia in the elderly. These disorders can be Department of Ophthalmology and Neurology, Mayo Clinic, Rochester, Minnesota. Supported in part by Mayo Foundation, Rochester, MN, and a grant from the Knights Templar Eye Foundation, Flower Mound, TX. The author reports no conflicts of interest. Address correspondence to Michael C. Brodsky, MD Department of Ophthalmology, Mayo Clinic, 200 First St SW, Rochester, MN 55905; E-mail: [e-mail] 406 neurologic or orbital in origin but are frequently idiopathic (1–5). Prismatic correction is sometimes successful (6), but may not be tolerated when incomitance or torsion is present or when prism adaptation occurs (7). Botulinum treatment can produce successful results, but early overcorrection is often problematic (8). Surgical treatment is particularly challenging because the dose–response ratio of vertical rectus muscle recession necessitate miniscule recessions, which can give rise to a degree of postoperative drift that exceeds the surgical effect of the recession (9,10). It is generally accepted that a 1 mm recession of a vertical rectus muscle produces approximately 3 prism diopter (PD) of change in vertical alignment. Thus, a vertical deviation of 2 PDs would necessitate a recession of less than 1 mm. To address this problem, several procedures have been devised and successfully implemented (11–17). These include graded partial tenotomy (titrating the degree of tenotomy itself) (11–15) and central mini-tenotomy (16) and miniplication (17). Recently, Singh et al (18), devised a partial tendon recession for small-angle vertical strabismus. This procedure entailed performing a tenotomy of 80%–90% of a vertical rectus muscle followed by a hemirecession to produce a slant of the muscle. They reasoned that the surgical effect should approximate half of that produced by a recession, and their results supported this assumption. This approach was concordant with Kushner’s analysis of slant biomechanics, which concluded that the surgical effect of any slant procedure is a function of the recession effect that it ultimately produces (19). The advantage of this procedure is that it could be precisely titrated to the hyperdeviation, thereby obviating the need for adjustable sutures. This procedure produced resolution of vertical diplopia in 82% and restoration of orthophoria in 60%. The mean response to surgery was 1.5% PD/mm. In 2016, I began using this procedure to excellent effect. I describe my results in 11 patients and confirm the ease and utility of this procedure. Brodsky: J Neuro-Ophthalmol 2023; 43: 406-409 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution METHODS Patients with small isolated vertical deviations and corresponding vertical diplopia were selected for a temporal slant procedure of the inferior rectus muscle (TSRIRM) when they did not desire or tolerate prism therapy. Patients with vertical deviations greater than 6 PDs were excluded because these deviations exceeded the physical limits of a slanting procedure (the inferior rectus muscle width allows one pole to be slanted back a maximum of 4 mm which would be expected to correct 6 PDs) (10). The decision to operate on the inferior rectus was based on its surgically accessibility during the Bell phenomenon. The decision to slant the temporal portion was based on the finding that all patients had some degree of extorsion in the same or fellow eye. Although this procedure is easy to perform under local anesthesia, all but 2 patients requested general anesthesia. According to the protocol outline by Singh et al (10), a small conjunctival incision was made just temporal to the temporal pole of the inferior rectus muscle. The conjunctiva was then stretched over the tip of the muscle hook at the nasal pole. Large vessels within the temporal and midmuscle tendon were cauterized. A 6-0 vicryl suture was placed through the temporal tendon pole and tied. The temporal tendon was then severed from its insertion to the globe distal to the suture, and the incision continued to affect an 80%–90% tenotomy, with an effort to spare the anterior ciliary arteries within the far nasal side of the tendon (Fig. 1). The temporal tendon was then resutured to the globe posterior to its original insertion. The distance was determined according to the original formula from Singh et al (18) of 2 mm recession for every 3 PD of vertical deviation (Fig. 1). In 2 patients, this procedure was applied to 2 patients who had superior oblique palsy with 20 PD of hyperdeviation, indicating that isolated inferior oblique recession would be insufficient to restore binocular alignment. In both patients, the temporal portion of the inferior rectus muscle was slanted back 4 mm to affect the equivalent of a 2 mm inferior rectus muscle recession. RESULTS A total of 11 patients with small-angle vertical strabismus met our inclusion criteria (Table 1). None of these patients showed clinical signs or symptoms of restrictive strabismus (e.g., history or signs of thyroid eye disease or other orbitopathy, vertical incomitance, or positive forced duction testing at surgery). Of the 9 patients deemed treatment successes, all had immediate resolution of diplopia which persisted at 2 and 6 months. At the final postoperative follow-up examination, 4 patients (Cases 2, 7, 9, and 11) were orthophoric, 1 patient (Case 4) had a small residual hyperphoria that was asymptomatic, 2 patients (cases 5 and 8) had reverse hyperphorias of 1 PD that were asymptomBrodsky: J Neuro-Ophthalmol 2023; 43: 406-409 FIG. 1. Surgeon’s view of the left inferior rectus muscle during TSRIRM. Left: An 80%–90% tenotomy is extended from temporal to nasal with an attempt to avoid the nasal arterial supply when possible. Right: The temporal pole is then resutured to sclera in a recessed position. TSRIRM, temporal slant recession of the inferior rectus muscle. atic, and 1 patient (Case 3) had a small asymptomatic postoperative exophoria. Another patient with a history of infantile exotropia (Case 6) had resolution of diplopia with a small residual dissociated vertical divergence. Of the 2 patients deemed to be treatment failures, one had a small hyperphoria on postoperative day 1 but gradually developed a recurrent intermittent hypertropia (Case 1) and another had a constant preoperative hypertropia and had a residual intermittent hypertropia with intermittent diplopia (Case 8). One patient (Case 2) who was orthophoric on the first postoperative day did not return for follow-up, but on a telephone call 9 months later, he confirmed that his diplopia had immediately resolved and that he had felt no need to return. Two patients with superior oblique palsy and 20 PD hypertropia (Cases 10 and 11) underwent ipsilateral inferior oblique recessions (14 mm) in combination with contralateral (TSRIRM) with orthophoria and complete resolution of diplopia at their final follow-up visit. DISCUSSION The TSRIRM seems to work independently of the original cause of the vertical deviation. The reason for the temporal slant in this series is that all patients had some degree of subjective or objective extorsion preoperatively in one or both eyes. After transposition, a rectus muscle will torsionally rotate the eye as it is pulled back into its original position by surrounding check ligaments. A nasal transposition of the inferior rectus muscle would cause the inferior globe to be pulled temporally (intorting the globe) 407 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution TABLE 1. Temporal slant procedures CASE/AGE/SEX Diagnosis Measurements Torsion RX F/U Final 1/49/M 2/59/M Traumatic SOP Idiopathic 4 LH(T) 2 RH(T) DMR 0 OD and 3 ext OS 2 ext OD and 0 OS RIRTS, 3 mm LIRTS, 2 mm 2 yr 1 day 3/69/F 6 RHT DMR 1 ext OD and 5 ext OS LIRTS, 4 mm 2 mos 4/72/F R cavernous sinus meningioma Idiopathic 4-5 LH(T) Ortho (no diplopia at 9 mos) 3X9 5/5/F 6/55/M Congenital SOP Infantile exotropia 7/6/M 2 ext OD and 2 ext OS LIRTS, 4 mm 1 yr 2RH 0 OD and 1–2 ext OS 3 ext OD and 0 OS 6 mos 1RH 4RDVD (no diplopia) Ortho 8/56/F SOP 20 RH(T) 5 ext OD and 6 ext OS 2 mos 1LH 9/78/M 10/61/F Idiopathic ET/LHT s/p LSRc 2 RH(T) 6 RHT 0 OD and 2 ext OS 0 OD and 5 ext OS RIRTS, 3 mm LIRTS, 4 mm LMRs, 3 mm RIOC 14 mm, RIRTS, 4 mm LIOC, RIRTS, 3 mm LIRTS, 2 mm LIRTS, 4 mm 1 yr 2 mos Congenital SOP 6 RHT 4 XT 4 LH(T) 6 LhypoT, 4XT, 14XT9 20 RHT 11/61/F Traumatic SOP 20 RHT 2 ext OD and 2 ext OS 2 ext OD and 2 ext OS as the muscle reassumes its anatomic position. Nasal transposition of the inferior rectus muscle has been shown to reduce extorsion in patients with superior oblique palsy (20) Leaving the nasal inferior rectus tendon insertion adherent to the sclera is tantamount to a nasal transposition of the insertion, which should help to diminish extorsion. Ideally, in deciding which pole to slant, the torsional effects of a slant procedure should be directed at reducing any preexisting torsion, regardless of whether it poses an impediment to fusion. In this retrospective study, postoperative torsional changes were not routinely measured, but no patient reported subjective image tilt or torsional diplopia postoperatively. 3 mos Ortho 2 mos 4RH(T) Intermittent diplopia RIOc 14 mm, 2 mos Ortho LIRTS 4 mm Although the vertical deviations in our patients showed minimal lateral incomitance, it may also be important to consider lateral incomitance when deciding which side of the inferior rectus insertion to slant. Consider that the nasal pole of the inferior rectus insertion rotates anteriorly and the temporal pole rotates posteriorly in ipsilateral gaze (Fig. 2). Therefore, a temporal slant procedure would have a greater effect in contralateral gaze, where the slack muscle pole is rotated anteriorly (normally placed on stretch), and a lesser effect in ipsilateral gaze, where the slackened portion of the muscle is normally rotated posteriorly creating greater laxity. This differential effect may prove useful in treating small hyperdeviations that are accompanied by mild amounts of lateral incomitance. FIG. 2. Left eye extraocular muscles as viewed from below (B). IR denotes the inferior rectus muscle, MR denotes the medial rectus muscle, and LR denotes the lateral rectus muscle. The inferior oblique muscle is omitted for simplicity. Note that in adduction, the temporal pole of the IR tightens, and the nasal pole loosens, whereas, in abduction, the nasal pole tightens and the temporal pole loosens. Thus, for a right hypertropia that is greater in the right gaze, the temporal pole of the IR should be recessed whereas, for a right hypertropia that is greater in the left gaze, the nasal pole should be recessed. 408 Brodsky: J Neuro-Ophthalmol 2023; 43: 406-409 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution Finally, this procedure worked well in 3 patients with superior oblique palsy and 20 PD of hypertropia in the primary position (cases 7, 10, 11), in whom combined inferior oblique recession and contralateral inferior rectus recession has been shown to run the risk of surgical overcorrection (21). By substituting a temporal slant for the inferior rectus recession, we obtained stable postoperative binocular alignment without the need for adjustable sutures. Further study will be necessary to confirm the efficacy of this combined surgical approach to patients with unilateral superior oblique palsy and moderate hyperdeviations. The technical advantages of this procedure include reduced intraoperative and postoperative discomfort, sparing of the anterior ciliary artery, the ability to simultaneously reduce any objective extorsion, the reliability and stability of results (obviating the need for adjustable sutures), and the absence of late surgical overcorrections that so often accompany inferior rectus recession (22). Desired advantages are ease, predictability anterior ciliary vessel sparing, and to titrate any additional effects on torsion or horizontal incomitance. Given that the Bell’s phenomenon exposes the area of the inferior rectus muscle, this procedure should be feasible to perform in the clinic using local anesthesia when general anesthesia is contraindicated. Although Singh et al (18) found that the immediate postoperative hyperphoria sometimes increased very slightly, we observed this regression of effect in only 1 patient (Case 1). The limitations of this study include its small size, the absence of documentation of improvement in subjective and objective torsion, and the lack of postoperative side gaze measurements to reliably determine whether this slanting can be used to ameliorate horizontal incomitance. It is noteworthy, however, that no patient with horizontal incomitance experienced postoperative diplopia on gaze to either side. Although this study was limited to the inferior rectus muscle, Singh et al found that this procedure worked equally well when applied to the superior rectus muscle, and we have obtained similar success using a nasal superior rectus slant procedure (to simultaneously reduce extorsion) in one patient (18). Finally, this procedure was performed in patients with nonrestrictive strabismus, so its efficacy in the treatment of restrictive strabismus (e.g., thyroid eye disease) remains to be determined. In conclusion, TSRIRM provides a quick and reliable way to treat small comitant vertical deviations with small degrees of extorsion. Whether it finds application in the treatment restrictive forms of vertical deviation or those with significant lateral incomitance remains to be determined. Brodsky: J Neuro-Ophthalmol 2023; 43: 406-409 REFERENCES 1. Archer SM. Small deviations: vertical, horizontal, and combined. Am Orthopt J. 2015;65:31–34. 2. Brooks SE, Habib L. 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