When and How to Strengthen the Superior Oblique Muscle

Costenbader Lecture When and how to strengthen the superior oblique muscle

Richard A. Saunders, MD

PURPOSE To review the history of procedures used to strengthen the action of the superior oblique (SO) muscle and methods of quantifying surgical dosage and to determine the relationship between congenital onset and tendon laxity measured at the time of surgery. METHODS We reviewed medical records over a 10-year period of 30 patients who had undergone SO tendon tuck for SO muscle palsy using intraoperative assessment of forced ductions to determine surgical dosage. We also designed and tested a modiﬁed Bishop tucker, which can simultaneously measure tendon shortening and the force required. This allowed development of length tension curves between 0 and 200 g for individual SO tendons in patients with and without evidence of muscle palsy. RESULTS In distinction to most other procedures on the extraocular muscles, intraoperative forced ductions are used to determine appropriate surgical dosage. Patients undergoing SO tendon tuck using a uniform and repeatable forced duction method receive a greater amount of tuck (mean, 3 mm) when there is known congenital onset. Patients with congenital SO muscle palsy received a mean tuck of 10.8 mm (range, 8-16 mm), whereas patients with equivocal or known adult-onset SO palsy received a mean of 7.8 mm (range, 4-12 mm; p 5 0.002). CONCLUSIONS Patients with congenital SO muscle palsy have increased tendon laxity when measured di- rectly during SO tendon tuck. The excursion of presumed normal SO tendons through the trochlea is variable and may be less than previously thought. Modifying the Bishop tucker to provide length and tension data provides information that may be useful in determining surgical dosage. ( J AAPOS 2009;13:430-437)

urgery to weaken or strengthen the action of the su- Strengthening procedures have multiple effects on ocular perior oblique (SO) muscle has been performed rou- rotations which can be modified depending on exactly S tinely for nearly 50 years and remains one of the more how the SO tendon is repositioned. Finally, shortening difficult and controversial aspects of strabismus surgery. the SO tendon may produce an unacceptable limitation of There are several reported methods of strengthening the elevation in adduction (iatrogenic Brown syndrome) in SO muscle, all of which rely on operating on the reflected a substantial proportion of cases.1,2 For this reason many tendon (e-Supplement 1, available at jaapos.org). Because surgeons have avoided SO tendon strengthening procedures of the orientation of the trochlea medial and anterior to altogether. It is this unusual anatomy, complex physiology, the SO tendon insertion, the relative proportion of vertical, and unpredictable surgical outcome that undoubtedly led torsional, and horizontal forces induced on the globe are von Graefe to his famous and often repeated admonition complex and depend greatly on the direction of gaze. (‘‘Noli me tangere’’) that surgery on the SO muscle should not be attempted.3 Even as late as 1928, Banister4 stated, ‘‘Owing to the an- Author affiliations: Department of Ophthalmology, Medical University of South Carolina, atomical relations of the superior and inferior oblique mus- Charleston, South Carolina. Presented at the 35th Annual Meeting of the American Association for Pediatric cles to the eyeball, their deep location in the orbit, and their Ophthalmology and Strabismus, San Francisco, California, April 17-20, 2009. attachments to the globe in the neighborhood of the equa- Supported in part by NIH/NEI EY14793 (vision core); and an unrestricted grant to tor. advancement or shortening by tucking, is out of the MUSC, Storm Eye Institute, from Research to Prevent Blindness, Inc., New York, New . York. question and the ophthalmic surgeon must make use 2 The authors have no financial or proprietary interest in any product mentioned herein. of other muscles.’’ However, by that time Wheeler had al- Submitted March 24, 2009. ready shown that direct surgery on the SO tendon could be Revision accepted June 24, 2009. Reprint requests: Richard A. Saunders, MD, Medical University of South Carolina, performed to strengthen the action of an underacting SO Storm Eye Institute, Charleston, SC 29425 (email: [email protected]). muscle. Wheeler’s operation, described as a tendon ad- Copyright Ó 2009 by the American Association for Pediatric Ophthalmology and vancement, was actually more of a plication (folding), with Strabismus. 1091-8531/2009/$36.00 1 0 a tendon loop anchored to the sclera temporal and poste- doi:10.1016/j.jaapos.2009.06.009 rior to the insertion, and was performed after disinsertion

430 Journal of AAPOS Volume 13 Number 5 / October 2009 Saunders 431 of the superior rectus (SR) muscle. In 1946 Foster5 re- of South Carolina. These time periods were chosen because of ported a tendon ‘‘reefing’’ procedure, a plication attached the availability of clinical data, which had been lost for the inter- at the tendon insertion, which he suggested was more phys- vening years. Patients with onset of strabismus or torticollis dur- iologic. McLean modified these techniques by sewing the ing early childhood and no apparent cause, or those with tendon to itself as well as the sclera,6 describing what characteristic plagiocephaly33 and later onset of symptoms, were amounts to a combined SO tendon tuck and plication. deemed to be of ‘‘congenital’’ etiology. The remaining patients He importantly advocated a temporal approach to the ten- were classified as either ‘‘posttraumatic’’ or ‘‘undetermined,’’ de- don, thereby avoiding disinsertion of the SR muscle. pending on clinical circumstances. The presence or absence of McGuire reported success using both SO resection and a clinically lax tendon at the time of surgery was not used in as- tuck7,8 but apparently preferred the former procedure.8 signing etiology. The amount of tendon tuck was determined in In 1966 Dyer9 described and illustrated the SO tuck proce- a similar manner is all cases. A Bishop tendon tucker was used dure, essentially as it is performed today, using a single, to shorten the tendon after the entire SO tendon was isolated tem- nonabsorbable suture to fold the tendon near the insertion. poral to the SR on a Stevens muscle hook (e-Supplement 2, avail- Despite the above reports, prior to 1970 about the only able at jaapos.org). Once a provisional tuck was secured using time an ophthalmologist saw the SO tendon was during a 5-0 braided Dacron suture, a silk traction suture was placed an enucleation (Eugene Helveston, personal communica- through the loop for easy retrieval, and the tendon released. tion, October 14, 2008). Forced ductions were then performed in a manner previously As skepticism regarding SO muscle strengthening re- described,12,34 to assess the limitation of elevation in adduction ceded, the role of SO tendon tuck became better estab- generated by the shortened tendon. An adequate tuck was judged lished, at least in certain clinical situations.10-18 The tuck to have been achieved when the first resistance to elevation in ad- has proved to be convenient to perform and generally re- duction was noted as the inferior limbus crossed an imaginary line versible simply by removing the nonabsorbable suture. between the medial and lateral canthus (Figure 1). Tucks judged Most importantly, it leaves the scleral insertion of the SO too tight or too loose were adjusted appropriately (Figure 2). Care tendon unmolested, with the theoretic advantage that any was taken not to retropulse the globe when performing forced increased forces applied to the globe from tendon tucking ductions, because this would put the tendon on stretch and alter would be generated in the same proportion they were lost the result. The final endpoint was sufficient to remove all tendon due to the paresis. Thus the vertical, torsional, and hori- laxity and generate an approximately À2 elevation deficiency zontal correction would occur as needed, and the only (scale, 0 to À4, where 0 5 full elevation and À4 5 no elevation) required decisions would relate to surgical dosing and in adduction, postoperatively. Data were analyzed with regard whether to operate additional extraocular muscles. to amount of tuck, congenital vs noncongenital onset, and preop- SO tendon tuck figured prominently in Knapp’s treat- erative hyperdeviation. ment paradigm in his well-known classification and treatment recommendations for SO muscle palsy, presented Studies Involving a Modified Bishop Tucker in 1970 as the First Richard C. Scobee Memorial Lecture, In 2005 we modified a Bishop tucker to allow the addition of an ‘‘Diagnosis and surgical treatment of hypertropia,’’ to the externally mounted strain gauge. The new instrument allowed si- American Association of Certified Orthoptists in Las multaneous determination of the amount of SO tendon shorten- 11 Vegas, NV. Variations have been described by Harada ing and the force required to achieve this shortening. Early 19 20-22 and Ito and others to increase the relative torsional prototypes proved impractical, because of instrument size (Fig- correction by redirecting and advancing the anterior ten- ure 3) and the use of different materials (stainless steel and alumi- don fibers. However, SO tuck performed temporal to the num), which required different methods of sterilization. We SR muscle remains the simplest and most useful operation subsequently enlisted the help of Bausch and Lomb (St. Louis, in the surgeon’s armamentarium to strengthen the action MO), who produced an improved instrument, similar in size to of an underacting SO muscle, particularly in the context a currently marketed Bishop tucker but with an internal strain of SO muscle palsy. Despite better accessibility, tendon gauge that was more practical to use. The final version had strain shortening medial to the SR muscle has not generally gauge calibration between 0 and 200 g, in 50 g increments, which been advocated, perhaps because of proximity to the troch- could be read through a cutout in the center of the shaft (Figure 4). lea and the risk of producing iatrogenic Brown syndrome After obtaining approval from the institutional Human Research postoperatively. Our knowledge has been greatly advanced Office, selected patients undergoing surgery on the SO tendon 3 by anatomic and clinical studies by Parks, Helveston and (typically posterior tenectomy or tendon tuck) had length-tension 10,23,24 25-32 coworkers, and others. measurements taken during the procedure from 0 g to 200 g of force, which was the limit of the instrument. Subjects and Methods The Lax Tendon and Congenital Onset Results A retrospective database review was performed over two 5-year Medical records from 30 patients were found complete and periods (1980–1985 and 2003–2008) for patients undergoing analyzed (e-Supplement 3, available at jaapos.org). All had a SO tendon tuck for SO muscle palsy at the Medical University diagnosis of SO muscle palsy (supported using Parks 3-step

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FIG 2. Simple technique of adjusting a tuck judged too loose or too tight. A, An excessive tuck can be loosened by pulling the looped tendon apart with a muscle hook while simultaneously working the pro- visionally tied nonabsorbable (eg, 5-0 braided Dacron) suture away from the sclera with a needle driver. Once adjusted, the tendon is then secured tightly with a second wrap of suture around and through the tendon. A silk traction suture is shown through the tendon loop and allows easy release and recovery from the orbit. B, An inadequate tuck is tightened by placing a second wrap of suture around and through the tendon closer to the sclera. The original suture is not removed. Drawings courtesy of Kevı¨n Rockwell.

test)35 and had SO tendon tuck performed using a Bishop tucker as part of their surgical procedure. As a general rule, patients with $30D of hypertropia in extreme lateral gaze opposite the side of paretic muscle, or with $20D in primary gaze position, had a second muscle operated—usu- ally a weakening of the ipsilateral inferior oblique (IO) or contralateral inferior rectus muscle. These were selected based on prism-and-cover measurements (or estimates) in the diagnostic gaze positions, although treatment strategies recommended by Knapp11 were not necessarily followed (eg, contralateral SO tendon tenotomy in class 5 [so-called ‘‘double-depressor’’] SO muscle palsy). The 15 patients with congenital SO muscle palsy received a mean tuck of 10.8 mm (range, 8-16 mm), while the 15 patients with equivocal or known adult-onset SO palsy received a mean tuck of 7.8 mm (range, 4-12 mm) (p 5 0.002), indicating greater tendon laxity in the congenital group. Among these 30 patients, the largest tuck performed was 16 mm; the smallest, 4 mm. A modest cor- relation was found between the amount of tuck and the preoperative hyperdeviation, both in primary gaze position (r 5 0.30) and in greatest measured deviation in any diagnostic gaze position (r 5 0.32). There were no compli- cations referable to using the modiﬁed tucker or measurements of tendon laxity. Data from 12 subjects from our institution were col- lected during SO muscle surgery to test the feasibility of generating length-tension curves for the SO muscle, with and without SO palsy, using the modiﬁed Bishop tucker.

: FIG 1. Drawing of the intraoperative traction test for titrating a superior oblique tendon tuck (left eye shown). A, The eye is grasped near the limbus at approximately 5:30 o’clock with toothed forceps. B, The globe is positioned in 30-40 adduction. C, The globe is then elevated against the superior oblique tendon without retropulsion. The ﬁrst resistance to elevation should be felt as the inferior limbus crosses an imaginary line (dashed line) between the medial and lateral canthus.

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FIG 3. Prototype instrument consisting of a modiﬁed Bishop tucker attached to an aluminum hand piece. A commercially manufactured spring- scale connects to the tucker shaft, which has been modiﬁed to allow free movement of the tendon hook. A, Component parts. B, Assembled instrument.

FIG 4. A, Integrated surgical instrument based on a commercially available Bishop tucker (Storz Instruments, St. Louis, MO). B, The amount of tendon shortening (in mm) is indicated in the usual fashion on the side of the shaft. However, an internal strain gauge, read through the window, provides the amount of force (g) required to displace the tendon.

To stabilize the globe during measurements, it was found Progressively greater forces could be demonstrated in all helpful to use forceps to position the globe in depression, cases as the tucker tightened the tendon. This progression with the superior limbus at the margin of the lower eyelid. occurred regardless of whether the patient had mild SO

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A alteration in orbital ‘‘pulleys,’’30 cannot be used to explain posttraumatic or surgically induced cases and would have 16 to account for the greater tendon laxity we typically ﬁnd 14 in presumed congenital onset. It remains clinically reason- 12 able, therefore, that surgical interventions be designed as- 10 suming we are treating strabismus produced by weakness 8 of the SO muscle in the majority of cases. While increased 6 tendon laxity appears to occur in cases of congenital onset 4 Right eye Left eye 10 2 SO muscle palsy, and a clinical grading system de-

Distance (millimeters) 26 0 scribed, more rigorous documentation has been lacking. 0 50 100 150 200 250 We have shown that patients with congenital onset SO Force (grams) muscle palsy do have, on average, greater tendon laxity than those of acquired or undetermined onset by approxi- B mately 3 mm. However, the variation in tendon tuck was 16 large (8–16 mm) and some patients with known posttrau- 14 matic SO muscle palsy received tucks as large as 12 mm. 12 While very redundant or otherwise anomalous (including 10 absent) tendons will occasionally be encountered, such 8 cases do not necessarily support the concept that excessive 6 tendon laxity per se is ever the primary disorder in these 4 23 Left eye patients. 2 Distance (millimeters) Surgery to correct hypertropia and torticollis in patients 0 050 100 150 200 250 with congenital SO muscle palsy is the most common indi- Force (grams) cation for SO muscle strengthening. Other less common indications are acquired SO muscle palsy with marked C underdepression in adduction, or torsional diplopia, typi- 16 cally found in acquired, bilateral SO muscle palsy. SO 14 muscle strengthening may occasionally be appropriate in 12 the treatment of residual IO overaction in patients with 10 a V-pattern strabismus of presumed nonparetic etiology 8 after IO weakening. However, little is known about its 6 effectiveness is this clinical context. 4 Right eye Congenital SO muscle palsy responds well to SO muscle 2 Distance (millimeters) 0 strengthening and SO tendon tuck is the easiest way to do it 0 50 100 150 200 250 (e-Supplement 2). A tuck is occasionally performed as an isolated procedure but is most useful when the hypertropia Force (grams) is large and combined with ipsilateral IO muscle weakening.34 Congenital palsies are characterized by excellent ver- FIG 5. Sample length-tension curves in 3 patients undergoing supe- tical vergence amplitudes, which may render phoric a 20D rior oblique (SO) tendon surgery. A, Presumed normal tendon under- or 25D (or greater) hyperdeviation in primary gaze position. going posterior tenectomy. B, Posttraumatic SO muscle palsy. C, Congenital SO muscle palsy with clinical tendon laxity. Acquired SO muscle palsy, in contrast, often presents with a hypertropia of lesser magnitude, typically with poor ver- muscle overaction or SO muscle palsy (Figure 5). Measure- tical vergence amplitudes. Barring profound underdepres- ments were reasonably repeatable. Retesting, when per- sion in adduction, these cases are preferably managed by formed, always yielded a tendon laxity Æ 2 mm of the single-muscle surgery not involving the SO muscle. Sur- original value at a given amount of force, 0, 50, 100, 150, gery to weaken the ipsilateral IO, contralateral inferior rec- and 200 g. tus, or, occasionally, the ipsilateral SR muscle, is reasonably predictable and may be suited to adjustable suture techniques. Importantly, they do not require the more Discussion difﬁcult titration of a SO tendon tuck in a ‘‘non-lax’’ ten- While patients with the clinical appearance of SO palsy don. Ironically, the only tuck takedown in my 30 years of may have multiple causes, most appear associated with dys- clinical practice (with well over 100 SO tucks under multi- function of the fourth (Trochlear) cranial nerve. With few ple clinical circumstances) was in a patient with the least exceptions, the lax tendon observed clinically and muscle amount of tuck I ever performed (4 mm). This patient atrophy with reduced contractility reported on orbital im- (e-Supplement 3, Patient 24) had unilateral posttraumatic aging31,32 adequately explain the pathophysiology of this SO palsy. Her surgical overcorrection and postoperative disorder. Alternative hypotheses, such as those involving Brown syndrome may have been related to shortening

Journal of AAPOS Volume 13 Number 5 / October 2009 Saunders 435 a relatively tight tendon, even in the context of known mus- generally be curative in such cases unless 2-muscle surgery cle paresis. Also contributing to her poor result was the de- is performed. Conversely, patients achieving satisfactory cision to perform simultaneously an ipsilateral IO postoperative alignment in sidegaze will almost always recession. This was done despite the fact that her greatest have their hypertropia resolved in primary gaze position hypertropia in any gaze position did not exceed 25D.I as well. Alternatively stated, if you target the surgery to would manage such a patient differently today. fix the sidegaze hypertropia, primary position will take Only 2 other patients have had clinically important over- care of itself. corrections following SO tendon tuck during this 3-decade The desirability of using intraoperative assessment when period. One had congenital SO muscle palsy with 40D of performing SO tendon tuck was actually suggested by Knapp sidegaze hypertropia preoperatively. An initial 15D of hy- in his 1970 Scobee lecture.11 After engaging the SO tendon potropia in primary gaze position postoperatively sponta- temporal to the SR muscle, he recommended the Bishop neously improved to orthophoria over several years and tucker be tightened until ‘‘snug’’ prior to placement of the the patient became asymptomatic. The other patient had suture. I observed him perform SO tendon tucks several posttraumatic SO muscle palsy and was left with À3 eleva- times as an ophthalmology resident during the mid-1970s, tion deficiency (due to Brown Syndrome) and diplopia in but was never clear on exactly how he decided on final surgi- adduction postoperatively, which persisted for 7 years. cal dosage. Scott18 subsequently recommended achieving However, he was well-aligned in primary gaze position a ‘‘moderate’’ Brown syndrome, although further guidance and tuck takedown was repeatedly refused. was again not provided. Helveston and Ellis1 used an esti- Because of the difficulty in quantitating surgical dosage, mate of tendon laxity to determine the amount of tuck per- I reserve SO strengthening procedures directed primarily formed, but they experienced a 17% rate of overcorrection at torsional correction (such as the Harada-Ito procedure) requiring tuck takedown. Presumably, there were additional to cases where hypertropia is small and there is symptom- patients who were overcorrected, but not sufficiently to atic extorsion (typically $15). However, a detailed discus- warrant additional surgery. The mean amount of tuck in sion of this technique is a separate subject and beyond the this series of 59 patients with both congenital and acquired scope of this article. SO muscle palsy was 12 mm, which is similar to the mean Surgery to strengthen the SO muscle is unique in that amount of tuck we performed in our congenital onset surgical dosing is determined almost exclusively on the ba- patients (10.8 mm). sis of intraoperative findings. Previous authors have found An alternative method advocated for unilateral cases no relationship between the amount of tuck performed and with SO tendon laxity is to perform sufficient tuck to equal- correction of vertical deviation in primary gaze position. ize the forced ductions with the presumed normal eye (Da- This is true regardless of whether SO tendon tuck is per- vid Plager, personal communication, November 11, 2002), formed in isolation14,36 or combined with surgery on other provided ipsilateral IO weakening is also performed. How- extraocular muscles.34,37 However, the amount of tuck ap- ever, surgical success rates have not been reported using pears to correlate with the greatest hypertropia measured this ‘‘matching’’ technique. One might speculate it could preoperatively in sidegaze opposite the paretic muscle, at lead to frequent undercorrection if the SO tendon were least in patients with congenital, large-angle vertical devia- not under sufficient tension to augment the action of the tions.34 When using a resistance endpoint, the surgical paretic SO muscle. Tendon tucking can be also performed dose presumably serves as a proxy for tendon laxity. Relying with a Fink tucker or just a Stevens muscle hook but is more on reported mean dosages as a treatment guide in indi- difficult to titrate. vidual patients will therefore produce under- and In 1985 we described a technique to make endpoint de- overcorrection if tendon laxity is not taken into consider- termination more uniform based on position of the inferior ation. limbus during intraoperative forced duction testing. Ten- It is also not widely appreciated that the best guide in se- don tightness (Brown syndrome) is assessed as the globe lecting a surgical dosage (eg, 1 vs 2 muscles) may be the di- is moved into an elevated position in adduction.36 The de- agnostic position of gaze with greatest hypertropia, rather sired tuck is produced when the first resistance to elevation than primary gaze position. Knapp11 used 25D as the divid- occurs as the inferior limbus crosses an imaginary line ing point in recommending 2-muscle surgery. However, he drawn between the medial and lateral canthus (Figures 1 did not specify whether this was primary position deviation and 2). This technique is easy to perform and reliable or the greatest measured deviation. In a subsequent publi- and has been successfully employed by others14,23,37,38 in cation Knapp and Moore17 alluded to using ‘‘large devia- both congenital and acquired SO muscle palsy. tions, over 30D in the paretic field’’ as an indication for While the choice and number of muscles to be operated multiple muscle surgery but did not explicitly state this is best guided by the magnitude of the hypertropia (partic- principle. Even with fusion suspended, primary position ularly in the field of greatest hyperdeviation), the amount hyperdeviations in congenital palsies may occasionally be of SO tendon shortening is not. This near-total reliance small, especially at near viewing,15,34 while sidegaze hyper- on traction testing is an anomaly in modern strabismus sur- tropia commonly exceed 30D or occasionally 40D (e-Sup- gery, where our textbooks are replete with dosage tables to plement 3). In our experience, surgical treatment will not guide weakening or strengthening of the horizontal rectus

Journal of AAPOS 436 Saunders Volume 13 Number 5 / October 2009 muscles, vertical rectus muscles, and to some degree the IO overcorrections, long-term undercorrections are not un- muscle. Understanding this is necessary for avoiding poor common. It is possible that shortening the SO tendon to outcomes. The reason for this difference in technique is a predetermined tension endpoint may be more successful not entirely clear, but it probably relates to (1) the presence than using a forced duction end point. The target tension of paresis (as opposed to paralysis) in most cases of clinically might prove to be less when there is simultaneous weaken- diagnosed SO palsy and (2) the unique structure of the ing of the IO muscle or more when SO tendon tuck is per- trochlea, which rapidly becomes unyielding when the SO formed alone. It may also be possible to predict, based on tendon is excessively shortened. Getting the best surgical tension measurements, which patients have increased risk outcome is therefore something of an art—perhaps more for long-term surgical failure or unacceptable postopera- so than is true of more routine strabismus surgery. It is in- tive Brown syndrome. teresting, however, that the mean amount of tuck we performed in noncongenital cases (7.8 mm) correlates closely with the estimated upgaze excursion (8 mm) in Acknowledgments 24 a normal trochlea. Because our method yields a modest This work was supported in part by NIH/NEI EY14793 (vision core) upgaze restriction in adduction (Brown syndrome) at the and an unrestricted grant to MUSC, Storm Eye Institute, from Re- conclusion of surgery, the forward excursion of the tendon search to Prevent Blindness, New York, NY. The author gratefully ac- through the trochlea may be less than previously thought. knowledges Drs. Luanna Bartholomew and Rupal Trivedi for editorial In this group of presumed normal tendons, tucks ranged assistance, and John Payne and Bausch and Lomb, Inc., for instrument from 4 to 12 mm; 6 of 15 (40%) were less than 8 mm, in- development. dicating the forward excursion of the tendon through the trochlea may often be less than mean values. This further References substantiates the need for tuck titration in this group of pa- 1. Helveston EM, Ellis FD. Superior oblique tuck for superior oblique tients. palsy. Aust J Ophthalmol 1983;11:215-20. It is also worth noting that mild-to-moderate postoper- 2. Wheeler JM. Advancement of the superior oblique and inferior oblique ocular muscles. Trans Am Ophthalmol Soc 1934;32:237-44. ative Brown syndrome is not undesired. Rather, it appears 3. Parks MM. Doyne Memorial Lecture: The superior oblique tendon. necessary in most cases to achieve satisfactory long-term Trans Ophthalmol Soc UK 1977;97:288-304. outcome. Most patients have some permanent deficit in el- 4. Banister JM. Surgical suggestions as to individual paralysis of the evation after SO tuck but are minimally symptomatic and superior oblique muscles. Am J Ophthalmol 1928;2:537-8. report diplopia only in extreme upgaze. Unless worse 5. Foster J. Certain operations on the superior oblique. Br J Ophthalmol 1946;30:678-82. than À2, this should not generally be viewed as a complica- 6. McLean JM. Direct surgery of underacting oblique muscles. Trans tion. The need for temporary overcorrection in other Am Ophthalmol Soc 1948;46:633-51. forms of strabismus surgery, such as primary intermittent 7. McGuire WP. The surgical correction of paresis of the superior exotropia, is also well recognized.39,40 Except when the oblique. Trans Am Ophthalmol Soc 1946;44:527-50. SO tuck is truly excessive, the postoperative Brown syn- 8. McGuire WP. Paresis of the superior oblique surgical correction: Resect or tuck. Southern Med J 1968;62:941-3. drome is clinically innocuous and improves or resolves 9. Dyer JA. Surgery of the inferior and superior oblique muscles. Int with time (e-Supplement 4, available at jaapos.org). How- Ophthalmol Clin 1966;6:571-89. ever, in cases where profound IO weakening (such as myec- 10. Helveston EM, Mora JS, Lipsky SN, et al. Surgical treatment of supe- tomy) is also performed, some surgeons (David Plager, rior oblique palsy. Trans Am Ophthalmol Soc 1996;94:315-28. personal communication, November 16, 2008) prefer to 11. Knapp P. First Annual Richard G. Scobee Memorial Lecture: Diag- nosis and surgical treatment of hypertropia. Am Orthopt J 1971;21: reduce slightly the amount of tuck to lessen the Brown syn- 29-37. drome postoperatively. Such an approach is clinically rea- 12. Saunders RA, Roberts EL. Abnormal head posture in patients with sonable, because long-term undercorrection is easier to fourth cranial nerve palsy. Am Orthopt J 1995;45:24-33. manage than long-term overcorrection, which invariably 13. Saunders RA, Rogers GL. Superior oblique transposition for third requires reoperation. nerve palsy. Ophthalmology 1982;89:310-16. 14. Bhola R, Velez FG, Rosenbaum AL. Isolated superior oblique tuck- Our modified Bishop tucker provides a tool to further ing: An effective procedure for superior oblique palsy with profound study properties of the SO muscle and tendon, both in pre- superior oblique underaction. J AAPOS 2005;9:243-9. sumed normal individuals and in patients with SO muscle 15. Reynolds JD, Biglan AW, Hiles DA. Congenital superior oblique palsy. Because the former group had no more than mild palsy in infants. Arch Ophthalmol 1984;102:1503-5. SO ‘‘overaction,’’ we believe these data will be useful to es- 16. Helveston EM. Superior oblique strengthening procedures. Am Orthopt J 1984;34:100-3. tablish normal or near normal values for SO tendon laxity. 17. Knapp P, Moore S. Diagnosis and surgical options in superior oblique We plan to report additional findings in the future. surgery. Int Ophthalmol Clin 1976;16:137-49. Finally, this or similar instruments may also be useful in 18. Scott WE. Differential diagnosis of vertical muscle palsies. In: determining surgical dosage when SO tuck is performed. Helveston EM, et al, editors. New Orleans Symposium. St. Louis: While intraoperative forced ductions seem effective and Mosby; 1978. p. 118-34. 19. Harada M, Ito Y. Surgical correction of cyclotropia. Jpn J Ophthal- can be titrated to a defined endpoint, this is still a subjective mol 1964;8:88-111. assessment that many surgeons do not feel comfortable 20. Fells P. Management of paralytic strabismus. Br J Ophthalmol 1974; making. While I have experienced almost no long-term 58:255-65.

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21. Metz HS, Lerner H. The adjustable Harada-Ito procedure. Arch 31. Sato M, Yagasaki T, Kora T, Awaya S. Comparison of muscle volume Ophthalmol 1981;99:624-6. between congenital and acquired superior oblique palsies by magnetic 22. Ohtsuki H, Hasebe S, Hanabusa K, Fujimoto Y, Furuse T. Intraoper- resonance imaging. Jpn J Ophthalmol 1998;42:466-70. ative adjustable suture surgery for bilateral superior oblique palsy. 32. Sato M. Magnetic resonance imaging and tendon anomaly associated Ophthalmology 1994;101:188-93. with congenital superior oblique palsy. Am J Ophthalmol 1999;127: 23. Helveston EM, Krach D, Plager DA, Ellis FD. A new classiﬁcation of 379-87. superior oblique palsy based on congenital variations in the tendon. 33. Wilson ME, Hoxie J. Facial asymmetry in superior oblique muscle Ophthalmology 1992;99:1609-15. palsy. J Pediatr Ophthalmol Strabismus 1993;30:315-18. 24. Helveston EM, Merriam WW, Ellis FD, Shellhamer RH, 34. Saunders RA. Treatment of superior oblique palsy with superior ob- Gosling CG. The trochlea. A study of the anatomy and physiology. lique tendon tuck and inferior oblique muscle myectomy. Ophthal- Ophthalmology 1982;89:124-33. mology 1986;93:1023-7. 25. Plager DA. Traction testing in superior oblique palsy. J Pediatr Oph- 35. Parks MM. Isolated cyclovertical muscle palsy. Arch Ophthalmol thalmol Strabismus 1990;27:136-40. 1958;60:1027-35. 26. Plager DA. Tendon laxity in superior oblique palsy. Ophthalmology 36. Saunders RA, Tomlinson E. Quantitated superior oblique tendon 1992;99:1032-8. tuck in the treatment of superior oblique muscle palsy. Am Orthopt 27. Horton JC, Tsai RK, Truwit CL, Hoyt WF. Magnetic resonance im- J 1985;35:81-9. aging of superior oblique muscle atrophy in acquired trochlear nerve 37. Morris RJ, Scott WE, Keech RV. Superior oblique tuck surgery in the palsy. Am J Ophthalmol 1990;110:315-16. management of superior oblique palsies. J Pediatr Ophthalmol Stra- 28. Demer JL, Miller JM. Magnetic resonance imaging of the functional bismus 1992;29:337-46. anatomy of the superior oblique muscle. Invest Ophthalmol Vis Sci 38. Del Monte M, Wright KW. Superior oblique tightening procedure. 1995;36:906-13. In: Wright KW, editor. Color Atlas of Strabismus Surgery: Strategies 29. Ozkan S, Aribal ME, Sener EC, Sanac AS, Gurcan F. Magnetic and Techniques. Irvine (CA): Wright Publishing; 2000. p. 180-81. resonance imaging in evaluation of congenital and acquired superior 39. Oh JY, Hwang JM. Survival analysis of 365 patients with exotropia oblique palsy. J Pediatr Ophthalmol Strabismus 1997;34:29-34. after surgery. Eye 2006;20:1268-72. 30. Clark RA, Miller JM, Rosenbaum AL, Demer JL. Heterotopic muscle 40. Ruttum MS. Initial versus subsequent postoperative motor alignment pulleys or oblique muscle dysfunction. J AAPOS 1998;2:17-25. in intermittent exotropia. J AAPOS 1997;1:88-91.

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