Oblique Muscle Dysfunction Research Articles

Factors associated with changes in horizontal deviation after inferior oblique weakening surgery.

To identify the factors affecting postoperative horizontal deviation following isolated inferior oblique (IO) weakening surgery. The medical records of patients who had undergone isolated IO weakening surgery between February 2010 and September 2021, with a minimum follow-up period of 6 months, were retrospectively reviewed. Patients were divided into two groups, eso-shift, and non-eso-shift, based on the change in horizontal deviation at postoperative 6 months. Eso-shift or exo-shift was defined as a change of 2Δ or more. A total of 77 patients were included. Among them, 49 patients (63.6%) showed changes in horizontal deviation: 37 (48.0%) eso-shift, 12 (15.6%) exo-shift. Twenty-eight patients (36.4%) showed no change in alignment. The eso-shift group showed the following characteristics compared to the non-eso-shift group: older age (P < 0.001), higher proportion of patients with preoperative exo-deviation (P < 0.001), and greater preoperative hypertropia in primary gaze (P < 0.001), down gaze (P = 0.031), ipsilateral gaze (P < 0.001), and ipsilateral head tilt (P = 0.002). Regarding the postoperative changes in horizontal deviation based on prior horizontal strabismus, patients with preoperative exo-deviation showed a statistically significant eso-shift. The patients with prior eso-deviation tended toward exo-shift, while those without prior horizontal deviation rarely changed. Changes in postoperative horizontal deviation are associated with preoperative horizontal and vertical deviation, which might result from changes in the rectus muscle due to oblique muscle dysfunction. Also, this study suggests that isolated IO weakening surgery could effectively correct small-angle horizontal deviation in patients with inferior oblique overaction (IOOA) and horizontal strabismus.

Long-Term Efficacy of Inferior Oblique Myectomy Accompanied with Tenon’s Capsule Closure: Objective Analysis Using Nine-Gaze Photographs

Background: The aim is to evaluate the long-term efficacy of inferior oblique (IO) myectomy combined with Tenon's capsule closure to prevent muscle reattachment to the sclera. Methods: We retrospectively reviewed the medical records of 18 patients with primary and secondary IO overaction who underwent IO myectomy accompanied by Tenon's capsule closure. Patients were followed up for at least 1 year after the surgery. The main outcome measures included oblique muscle dysfunction, which was objectively graded through computerized analysis of nine-gaze photographs, and the amount of vertical deviation in the primary position using alternate prism cover testing. Results: After a mean follow up of 2.5 years, the grade of IO overaction decreased from +2.2 ± 1.0 to -0.8 ± 1.0 (p < 0.001). In patients with secondary IO overaction with superior oblique (SO) palsy, SO underaction improved from -2.2 ± 1.5 to -0.2 ± 1.8 (p = 0.006). Successful vertical deviation in the primary position of seven prism diopters or less was achieved in 83.3% of the patients. Underaction of the IO was observed in 11.1% of patients, whereas none of the patients showed antielevation syndrome. Conclusion: IO myectomy combined with Tenon's capsule closure might be safe and effective for the treatment of primary and secondary IO overaction in the long term.

Subclinical markers of strabismus in children 5-18 years of age

To report the prevalence of subclinical markers of strabismus from a community-based screening of children. A family history and ophthalmic examination (including six markers of strabismus: oblique muscle dysfunction, stereopsis <60 arcsec, monofixation, nasal-temporal pursuit asymmetry, dissociated strabismus, and anisometropia) were obtained from consecutive children, aged 5-18years, in the local school system and the pediatric outpatient clinic of Mayo Clinic, Rochester, Minnesota. A total of 1,000 children (498 males [49.8%]) were examined at a mean age of 10.6years (range, 5-18.98). Of the 1,000, 57 (5.7%) had strabismus, and 130 (13%) had some form of phoria. Of the 943 children without strabismus, 103 (10.9%) had one or more of the six subclinical markers, including 43 (4.5%) with inferior oblique dysfunction, 37 (3.9%) with anisometropia, 34 (3.6%) with subnormal stereopsis, 6 (0.6%) with nasal-temporal pursuit asymmetry, 3 (0.3%) with monofixation, and none with dissociated strabismus. A subclinical marker of strabismus occurred in 20 (12.7%) of the 157 nontropic subjects who had a family history of either strabismus, amblyopia, or both and in 83 (10.6%) of the 786 nontropic children without a family history. In this community-based screening of children, subclinical disorders of binocular vision occurred in 10%-13% of children without strabismus, of which inferior oblique muscle dysfunction, anisometropia, and subnormal stereopsis were most prevalent. Identifying these disorders among strabismic families may be useful in elucidating the genetic puzzle of childhood strabismus.

Pattern strabismus in consecutive esodeviation after bilateral lateral rectus muscle recession for intermittent exotropia

After bilateral lateral rectus recession for intermittent exotropia, children can develop V- or A-pattern esodeviation and adopt a chin-down or chin-up position to facilitate fusion. The aim of this study was to discuss possible causes and management of this pattern. The medical records of children who developed consecutive esodeviation with V- or A-pattern strabismus after surgery for intermittent exotropia but with no pre- or postoperative oblique muscle dysfunction were reviewed retrospectively. Ductions, versions, angles of deviation, and fundus torsion were evaluated before and after surgery. Patient management and outcomes were analyzed. A total of 37 patients were identified (mean age, 5.7±1.5years), with a mean preoperative deviation of 30.6Δ±5.2Δ; no patient had a preoperative pattern strabismus. Mean bilateral lateral rectus recession was 6.2±0.9mm. Of the 37, 34 (89%) returned postoperatively with V pattern, 2 with an A pattern, and 1 with an hourglass-like pattern. No patient showed oblique muscle dysfunction or fundus torsion. Reoperation for the consecutive deviation was performed in 19 patients, in all of whom the lateral rectus muscles were not vertically displaced. The pattern disappeared completely after reoperation and reestablishment of adequate alignment in the primary position. In our patient cohort, pattern strabismus after bilateral lateral rectus recession was successfully reversed by correction of the consecutive esodeviation.

Surgical outcomes after unilateral horizontal rectus surgery in children with infantile esotropia for the correction of A or V pattern

The management of A or V pattern deviation associated with esotropia can be challenging since the horizontal deviation changes with position of gaze. This study aimed to assess the effect of unilateral horizontal rectus surgery for the correction of horizontal deviation associated with A or V pattern in children with non-comitant infantile esotropia. Twenty-seven children with infantile esotropia and A-V pattern, more than 10 and 15 prism diopters respectively, were included in this retrospective observational single-center study. Horizontal rectus surgery was performed on the most deviated eye under general anesthesia. The patients were divided into two groups: A pattern and V pattern. The outcome measures were change in the amount of pattern and rate of regression after surgery. The amount of pattern was characterized by the difference in esodeviation between upgaze and downgaze. Horizontal deviation at distance and near fixation decreased significantly (P<0.0001). Vertical gaze esotropia disparity decreased significantly (P=0.01 and P=0.0002 for A and V patterns respectively). A pattern esotropia was reported in only 2 (7%) cases after surgery compared to 9 (33%) before surgery. The number of subjects with V pattern esotropia decreased from 18 (67%) to 3 (11%) after surgery. The mechanisms involved in the pathophysiology of A and V patterns may not always be related to oblique muscle dysfunction. These findings suggest that unilateral horizontal rectus surgery may be an effective procedure to correct both horizontal deviation and A-V pattern in non-comitant infantile esotropia.

Esotropia and Exotropia Preferred Practice Pattern®

Esotropia and Exotropia Preferred Practice Pattern®

Resolution of hypertropia with correction of consecutive horizontal deviation

BackgroundTo study the resolution of hypertropia in patients who undergo horizontal deviation surgery for consecutive esotropia or consecutive exotropia. MethodsWe retrospectively reviewed the records of 23 patients with consecutive esotropia or exotropia who had concomitant vertical tropia. All patients had had surgery for horizontal deviation that required further surgery to correct consecutive horizontal strabismus and had a minimum of six months of postoperative follow-up. All patients were noted to have vertical deviation greater than 5 prism diopters (PD) in primary position on preoperative examination. Patients underwent corrective surgery for horizontal strabismus without surgical manipulation of the vertical extraocular muscles. The exclusion criteria were coexisting oblique muscle dysfunction, manifest or latent dissociated vertical deviation, and extraocular muscle palsy. ResultsThe mean preoperative vertical deviations were 7.6 ± 2.3 PD for distance and 7.3 ± 2.3 PD for near. All patients had resolution of vertical deviation in all fields of gaze despite surgical correction only being made to horizontal extraocular muscles. No patients had measureable vertical tropia during six months of follow-up. ConclusionWe propose that measureable hypertropia unrelated to oblique muscle dysfunction, dissociated vertical deviation, or paretic/mechanical muscle that coincides with consecutive horizontal deviation can be resolved with horizontal muscle surgery alone. Therefore, it may not be necessary to perform vertical surgery to correct coincident vertical deviation in patients with consecutive horizontal deviation. More research is needed in the form of prospective clinical trials to determine whether vertical surgery has any utility for these patients.

Effect of fronto-orbital advancement on astigmatism in patients with anterior plagiocephaly.

The purpose of this study was to determine the effect of unilateral fronto-orbital advancement (FOA) or bilateral FOA on ocular aspects of plagiocephaly. A retrospective review of ocular findings in 16 patients with plagiocephaly was performed. Patients were divided into 2 groups: 12 patients who underwent bilateral FOA (bFOA) and 4 patients who underwent unilateral FOA (uFOA), and ocular findings were compared. One-half of patients showed strabismus in both groups, and all had exotropia. Hypertropia was found only on the same side of the plagiocephaly in 17% of the bFOA group and 25% of the uFOA group. One-third of the patients in the bFOA group and one-half of patients in the uFOA group had oblique muscle dysfunction. In terms of astigmatism, the degree of with-the-rule astigmatism on the contralateral side was larger in the bFOA group compared to the uFOA group (p=0.030). The degree of with-the-rule astigmatism was larger on the contralateral side than the ipsilateral side (p=0.005) in the bFOA group. Patients with abnormalities in ductions/versions had larger astigmatism on the contralateral side than those without abnormalities in ductions/versions. In conclusion, bilateral FOA could induce unwanted outcomes of larger astigmatism on the contralateral side. Astigmatism should be carefully evaluated after bilateral FOA.

Clinical Characteristics and Surgical Outcomes in Patients With Intermittent Exotropia: A Large Sample Study in South China.

The clinical characteristics and surgical outcomes in a large sample of patients with intermittent exotropia (IXT) as well as an analysis of risk factors associated with surgical failures are presented in this article. Data from IXT patients who received surgical management at the Eye Hospital, in the Zhongshan Ophthalmic Center, of Sun Yat-Sen University, China from January 2009 to December 2013 were reviewed retrospectively. Included within this analysis were data from pre- and postoperative ocular motility, primary alignment, and binocular vision.A total of 1228 patients with IXT were reviewed. Males (50.4%) and females (49.6%) were nearly equally represented in this sample. Thirty-two patients (2.6%) had a family history of strabismus. The mean age at onset was 6.77 ± 6.43 years (range 7 months –48.5 years), mean duration at presentation was 7.35 ± 6.68 years (range 6 months–47 years), and mean age at surgery was 13.7 ± 8.8 years (range 3–49 years). The mean refractive error was −0.84 ± 2.69 diopter in the right eye and −0.72 ± 2.58 diopter in the left eye. Amblyopia (4.2%), oblique muscle dysfunction (7.0%), and dissociated vertical deviation (4.7%) were also present in these patients. The most common subtype of IXT was the basic type (88.1%). Orthophoria was observed in 80.5% of patients and the ratios of surgical undercorrection and overcorrection were 14.7% and 4.8%, respectively, as determined with a mean follow-up time of 7.8 ± 3.7 months. When combining ocular alignment with binocular vision as the success criteria, the success rate decreased to 35.6%. Multivariate risk factor analysis showed that only the loss of stereoacuity (P = 0.002) was associated with a poor outcome. There were no differences in the long-term results between bilateral lateral rectus recession and unilateral lateral rectus recession with medial rectus resection.Most IXT patients displayed normal vision, with few having positive family histories, amblyopia, oblique muscle dysfunction, and dissociated vertical deviation. The most common subtype of IXT was the basic type. Long-term surgical results were less favorable when sensory status was included in the criteria for success. Patients with stereoacuity loss were at an increased risk for poor outcomes.

Establishing a surgical outreach program in the developing world: pediatric strabismus surgery in Guatemala City, Guatemala

To report our experince in establishing a sustainable pediatric surgical outreach mission to an underserved population in Guatemala for treatment of strabismic disorders. A pediatric ophthalmic surgical outreach mission was established. Children were evaluated for surgical intervention by 3 pediatric ophthalmologists and 2 orthoptists. Surgical care was provided at the Moore Pediatric Surgery Center, Guatemala City, over 4 days. Postoperative care was facilitated by Guatemalan physicians during the second year. In year 1, patients 1-17 years of age were referred by local healthcare providers. In year 2, more than 60% of patients were prescreened by a local pediatric ophthalmologist. We screened 47% more patients in year 2 (132 vs 90). Diagnoses included congenital and acquired esotropia, consecutive and acquired exotropia, congenital nystagmus, Duane syndrome, Brown syndrome, cranial nerve palsy, dissociated vertical deviation, and oblique muscle dysfunction. Overall, 42% of the patients who were screened underwent surgery. We performed 21 more surgeries in our second year (58 vs 37), a 57% increase. There were no significant intra- or postoperative complications. Surgical outreach programs for children with strabismic disorders in the developing world can be established through international cooperation, a multidisciplinary team of healthcare providers, and medical equipment allocations. Coordinating care with local pediatric ophthalmologists and medical directors facilitates best practice management for sustainability.

Prevalence of amblyopia and strabismus in Eastern China: results from screening of preschool children aged 36–72 months

PurposeTo determine the prevalence of amblyopia and strabismus in preschool children in Eastern China.MethodsThe Nanjing Pediatric Vision Project was a cross-sectional, population-based cohort study conducted in preschool children aged 36–72...

The Role of Extraocular Muscle Pulleys in Incomitant Non-Paralytic Strabismus.

The rectus extraocular muscles (EOMs) and inferior oblique muscle have paths through the orbit constrained by connective tissue pulleys. These pulleys shift position during contraction and relaxation of the EOMs, dynamically changing the biomechanics of force transfer from the tendon onto the globe. The paths of the EOMs are tightly conserved in normal patients and disorders in the location and/or stability of the pulleys can create patterns of incomitant strabismus that may mimic oblique muscle dysfunction and cranial nerve paresis. Developmental disorders of pulley location can occur in conjunction with large, obvious abnormalities of orbital anatomy (e.g., craniosynostosis syndromes) or subtle, isolated abnormalities in the location of one or more pulleys. Acquired disorders of pulley location can be divided into four broad categories: Connective tissue disorders (e.g., Marfan syndrome), globe size disorders (e.g., high myopia), senile degeneration (e.g., sagging eye syndrome), and trauma (e.g., orbital fracture or postsurgical). Recognition of these disorders is important because abnormalities in pulley location and movement are often resistant to standard surgical approaches that involve strengthening or weakening the oblique muscles or changing the positions of the EOM insertions. Preoperative diagnosis is aided by: (1) Clinical history of predisposing risk factors, (2) observation of malpositioning of the medial canthus, lateral canthus, and globe, and (3) gaze-controlled orbital imaging using direct coronal slices. Finally, surgical correction frequently involves novel techniques that reposition and stabilize the pulley and posterior muscle belly within the orbit using permanent scleral sutures or silicone bands without changing the location of the muscle's insertion.

An Objective Photographic Analysis of Ocular Oblique Muscle Dysfunction

To develop a new objective method for measuring ocular oblique muscle dysfunction. Prospective, observational study. Twelve healthy volunteers and 27 patients with oblique muscle overaction or underaction in at least 1 eye were included. The corneal contour in 9-gaze photographs was transcribed into an ellipse. A newly developed simulating program depicted the corneal contour as the eyes moved, and graded oblique muscle dysfunction by analyzing the angular difference between the 2 eyes. An angular difference of 5 degrees was defined as 1 unit of overaction or underaction. To verify the accuracy of the method, a masked observer compared the photographic analysis with goniometric readings in the model eye and magnetic search coil recordings in healthy volunteers. The diagnostic accuracy of the photographic analysis was compared with the clinical gradings of patients with oblique muscle overaction or underaction. There was no statistical difference between photographic analysis and goniometric readings of the model eye. Bland-Altman plots showed that there was no overall tendency for the photographic analysis to differ from the scleral search coil values, and the difference fell mostly within ±7 degrees. There was a good correlation between the photographic analysis and the clinical grading of oblique muscle dysfunction (R(2)= 0.618; P< .001). The sensitivity and specificity for detecting oblique muscle overaction were 90.2% and 88.1%, respectively, whereas those for detecting underaction were 81.5% and 80.2%, respectively. A newly developed photographic analysis could provide an objective and accurate means of evaluating ocular oblique muscle dysfunction.

Correction of Hypertropia Coexisting with Intermittent Exotropia

Purpose: To investigate the clinical features associated with hypertropia and report the surgical outcomes of hypertropia coexisting with exotropia. Methods: We reviewed the medical records of 148 patients with intermittent exotropia coexisting with hypertropia over 4 PD who received exotropia surgery. The cases accompanied by apparent paralytic strabismus such as superior oblique palsy were excluded. Patients were divided into groupI(clinically diagnosed hypertropia) and group II (non-specific hypertropia) and the clinical features of coexisting hypertropia and surgical outcomes were analyzed. Results: Among the 148 patients, groupIconsisted of 38 patients (26%) and group II of 110 patients (74%). The average amount of preoperative hypertropia angle in primary gaze was 9.58 ± 3.89 PD and 6.62 ± 2.69 PD in group I and II, respectively. Group I included 12 patients with dissociated vertical deviation (DVD), 10 patients with unilateral inferior oblique overaction, 13 patients with asymmetric bilateral inferior oblique overaction and 3 patients with superior oblique overaction. Group II included 19 patients with comitant hypertropia (17%), head tilt positive pattern (simulated superior oblique palsy) was found in 84 patients (76.3%) and variable incomitance was observed. In groupI, 29 patients received simultaneous horizontal muscle with hypertropia surgery. Postoperative hypertropia angle in groupI was 1.41 ± 2.93 PD and 4 cases were considered surgical failure. In groupII, hypertropia was resolved with horizontal muscle surgery only and the amount of postoperative hypertropia was 0.45 ± 1.60 PD. Conclusions: In this study, vertical deviations in intermittent exotropia with concomitant hypertropia related to obvious oblique muscle dysfunction or DVD were corrected effectively by oblique or vertical rectus muscle surgery. Nonspecific hypertropia can be resolved after horizontal muscle surgery alone, however, for precise differential diagnosis, careful examination for variable clinical features is necessary before determining surgery. J Korean Ophthalmol Soc 2014;55(12):1883-1889

Persistent diplopia and superior oblique muscle dysfunction following dissection of the orbital periosteum in cranial base surgery

Background/aimsPersistent diplopia secondary to a fourth cranial nerve palsy is poorly documented after open cranial base surgery.MethodsSix cases of fourth cranial nerve palsy after cranial base surgery were drawn from...

Pattern Strabismus: Where Does the Brain's Role End and the Muscle's Begin?

Vertically incomitant pattern strabismus comprises 50% of infantile horizontal strabismus. The oblique muscle dysfunction has been associated with pattern strabismus. High-resolution orbit imaging and contemporary neurophysiology studies in non-human primate models of strabismus have shed light into the mechanisms of pattern strabismus. In this review, we will examine our current understanding of etiologies of pattern strabismus. Speculated pathophysiology includes oblique muscle dysfunction, loss of fusion with altered recti muscle pull, displacements and instability in connective tissue pulleys of the recti muscles, vestibular hypofunction, and abnormal neural connections. Orbital mechanical factors, such as abnormal pulleys, were reported as a cause of pattern strabismus in patients with craniofacial anomalies, connective tissue disorders, and late-onset strabismus. In contrast, abnormal neural connections could be responsible for the development of a pattern in infantile-onset strabismus. Pattern strabismus is likely multifactorial. Understanding the mechanisms of pattern strabismus is pivotal to determine an appropriate surgical treatment strategy for these patients.

İntermittan ekzotropya cerrahisinin başarısını etkileyen faktörler

Factors influencing the outcome of intermittent exotropia surgery Objective: This study aims at the evaluation of factors influencing the outcome of intermittent exotropia surgery. Material and Methods: Sixty-seven patients with intermittent exotropia were included. The patient files were retrospectively evaluated for the factors influencing the postoperative outcome. Among these evaluated factors are age, the age at onset of strabismus, type of deviation (convergence insufficiency, divergence excess or simple exotropia), age at operation, amount of preoperative misalignment, the time between the age of onset of deviation and age at operation, the refraction defect, presence of anisometropia or amblyopia and A-V pattern, hyperfunction of oblique muscles, binocular single vision and amount resection and recession. The outcome was assigned as successful operation (ortophoric or residual deviation below 10 pd) and unsuccessful operation (residual deviation above 10 pd). Results: Mean age of onset of deviation was 4.46±3.94 (min:0, max:15) and mean age at operation was 21.14±12.13 (min:2, max:47). At the last visit of their follow-up 42 patients (62.7%) were assigned as successful operation whereas 25 patients (37.3%) were as unsuccessful. There was no significant relation between the age at onset of strabismus, type of deviation, age at operation, the time between the age of onset of deviation and age at operation, the refraction defect, presence of amblyopia and A-V pattern, oblique muscle dysfunction and binocular single vision with postoperative outcome (p=0.121). Operational success was better for the patients without anisometropia (p=0.042). There was a negative relation between the exchanged muscle amount and the success (p=0.012). The success rate was lower as the amount of exchanged muscles elevated. Conclusion: It has been found that the most important factors influencing the outcome of strabismus surgery are the presence of anisometropia and the amount of preoperative deviation.

Superior oblique muscle palsy after frontal sinus mini-trephine

ObjectiveThe aim of this study is to present a case of superior oblique muscle dysfunction after a frontal sinus mini-trephine. MethodsThis is a case report of an 18-year-old woman where a mini-trephination approach and endoscope were used to open and marsupialize a symptomatic, opacified type IV cell within the left frontal sinus. After surgery, the patient developed a persisting diplopia; a left superior oblique muscle palsy was diagnosed. Nine cadaveric dissections of the trochlea were undertaken to clarify mechanisms for potential trochlear damage. ResultsCadaveric dissection reveals that the trochlea is more than a simple pulley; it is a complex structure in close proximity to the orbital rim. The superior oblique tendon telescopes and is surrounded by a vascular sheath that could be easily traumatized. ConclusionDamage to the trochlea could occur, as the periosteum is elevated from bone or during healing. Alternatively, prolonged traction on soft tissue near the trochlea could cause swelling of the vascular sheath, fibrosis, and hypomobility of the superior oblique tendon. Careful siting of the incision for external frontal sinus surgery as well as careful retraction of skin flaps and periosteal elevation are all techniques used, which should reduce the risk of damage to the trochlea.

Evaluation of Vertical Deviations Secondary to Other Causes

Distinguishing the cause of a vertical deviation can be important for management. When surgery is being considered, it is also critical to distinguish a true hypertropia from a dissociated vertical deviation (DVD). This paper reviews the clinical manifestations of DVD, true hypertropia, and primary oblique muscle dysfunction.

A comparative study of medial rectus slanting recession versus recession with downward transposition for correction of V-pattern esotropia

To compare the effect of medial rectus slanting recession versus medial rectus recession with downward transposition for correction of V-pattern esotropia without significant oblique muscle dysfunction. A total of 18 patients having V-pattern esotropia, without significant oblique muscle dysfunction were included in this randomized, prospective study. These were divided equally into 2 groups. The SLANT group underwent bilateral medial rectus muscle slanting recession: the lower pole of the medial rectus muscle was recessed a larger amount than the upper pole on the basis of the angles of esotropia in upgaze and downgaze, respectively. The TRANS group underwent bilateral medial rectus recession according to the angle of esotropia in the primary position, with half-tendon width downward transposition. Patients were followed for at least 6 months. Postoperatively, esotropia in the primary position was corrected to within 10Delta of orthotropia in 8 of 9 patients in the SLANT group and 7 of 9 patients in the TRANS group. All uncorrected patients showed a residual esotropia. All studied patients showed collapse of V-pattern esotropia to less than 10Delta difference between upgaze and downgaze. The mean V-pattern collapse was from 31.1Delta to 5.33Delta (25.8Delta) in the SLANT group and from 27.8Delta to 5.6Delta (22.2Delta) in the TRANS group. The difference between both groups was insignificant (p = 0.17). Both techniques significantly collapsed the esodeviation and V pattern (p < 0.05). Both slanting medial rectus recession and medial rectus recession with downward transposition corrected V-pattern esotropia, with no clinically or statistically significant differences in success rate.