Superior Oblique Muscle Palsy: Clinical Characteristics and Surgical Approach in 1057 Patients

doi:10.21203/rs.3.rs-3117301/v1

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Superior Oblique Muscle Palsy: Clinical Characteristics and Surgical Approach in 1057 Patients

https://doi.org/10.21203/rs.3.rs-3117301/v1

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Background

To evaluate the clinical findings of patients with SOP who underwent surgery.

Methods

This historical cohort study was performed on 1057 SOP patients managed with surgery in Farabi Hospital, Iran, from 2011 to 2022.

Results

Unilateral SOP was found in 990 (93.7%) patients with a mean age of 21.8 ± 14.8 years [715 (72.2%) congenital and 275 (27.8%) acquired (P < .001)]. Bilateral SOP was diagnosed in 67 (6.3%) patients with a mean age of 19.4 ± 15.6 years, in which 18 (27%) cases had masked type. The mean angle of vertical deviation in primary position at far in unilateral and bilateral cases was 15.6 ± 8.3 and 13.3 ± 9.1 △, respectively (P < .001). In unilateral cases, abnormal head posture (AHP) was detected in 847 (85.5%) patients and 12 (1.2%) had paradoxical AHP. Amblyopia was found in 89 (9.9%) unilateral and 7 (10.3%) bilateral cases. Solitary inferior oblique myectomy, was the most common surgery in both unilateral (n = 756, 77.1%) and bilateral (n = 35, 52.2%) patients. The second surgery was performed for 84 (8.6%) unilateral and 33 (49.3%) bilateral cases (P < .001). The prevalence of amblyopia and the mean angle of horizontal deviation were significantly higher in patients who needed more than one surgery (all P < .05).

Conclusion

Congenital SOP was more than twice as frequent as acquired SOP and about 90% of unilateral and 50% of bilateral cases were managed with one surgery. Amblyopia and significant horizontal deviation were the most important factors for reoperation.

Trial registration:

The Institutional Review Board approval was obtained from the Tehran University of Medical Sciences (IR.TUMS.FNM.REC.1400.012) and this study adhered to the tenets of the Declaration of Helsinki and HIPAA.

Superior oblique palsy

Abnormal head posture

Clinical Characteristics

Strabismus

Superior oblique muscle palsy (SOP) is the most common type of cyclovertical muscle palsy encountered by the strabismologist.(1–3) The annual incidence rate was reported 5.73 per 100,000 per year in the United States.(3)

Superior oblique palsy can be manifested as congenital or acquired. The latter usually happens following closed head trauma or less commonly secondary to respiratory viral infections, central nervous system lesions, and vascular abnormalities, or microvascular ischemia(3) The same clinical features can result from a congenital laxity, attenuated or even absent SO tendon, a developmental abnormality. Sometimes it happens due to unusual pathways of the muscle or functional consequences of extraocular muscle pulleys.(1, 4)

Congenital SOP has several characteristic signs and symptoms that distinguish it from the acquired type.(1, 3) The most important of these are the early onset and absence of a specific inciting event. Other clinical findings suggestive of congenital SOP include long-standing abnormal head posture, facial asymmetry, amblyopia, and large vertical fusional amplitude. It is helpful to examine old family photographs to detect a compensatory head tilt extending back to childhood, to differentiate congenital from acquired SOP.(1, 4, 5)

Examination of versions usually reveals underaction of the involved superior oblique muscle and over elevation in adduction of its antagonist inferior oblique muscle. However, the function of the superior oblique muscle sometimes can appear normal.(6)

The common symptoms in patients with SOP are headache, double vision (especially in lateral gazes), and difficulty in reading. Abnormal head postures (head tilt and face turn) can help patients to get rid of diplopia. Facial asymmetry and large vertical fusional amplitudes indicate chronicity. A review of old photography to verify chronicity can avoid unnecessary neurologic evaluation.(7) Surgical management of SOP is challenging, and various surgical methods have been described to tackle SOP, which can involve operating on the ipsilateral oblique muscles, as well as ipsilateral and/or contralateral vertical rectus muscles.(8, 9)

In this study, we explore the presenting symptoms, clinical features, and management of 1057 consecutive patients with superior oblique palsy who were examined and treated in the strabismus clinic of Farabi eye hospital. To the best of authors’ knowledge, the present study has the largest sample size among previously published articles about patients with superior oblique palsy.

This retrospective study was performed based on hospital records of 1057 SOP patients who were managed with surgery at Farabi Eye Hospital, Tehran University of Medical Sciences, from January 2011 to September 2021.

Records of all patients with unilateral or bilateral SOP who underwent strabismus surgery were included. Patients with cerebral palsy, delayed maturation, other coexisting ocular motor nerve palsies, previous ocular surgeries, previous strabismus surgeries and patients with incomplete data recorded in their medical documentation were excluded.

All patients underwent a complete ophthalmic examination and collected data included sex, age, past medical history, presence or absence of remarkable head trauma, laterality of superior oblique muscles palsy (unilateral or bilateral), presence of diplopia, types of abnormal head posture, visual acuity, refractive error, presence of amblyopia, presence of extraocular muscle abnormalities and type of surgeries were collected.

Visual acuity based on the logMAR unit was documented at a 6-meter distance. Cycloplegic refraction was measured by Topcon KR-800 auto-refractometer, and for younger and poor cooperative children, the findings were confirmed by performing hand-held retinoscopy. Anisometropia was considered when more than + 1.00 D difference (either sphere or cylinder) existed between two eyes. In amblyopic eyes, VA of 20/40 or worse with an interocular difference of more than two lines was required for enrollment of patients in the unilateral amblyopic group.(10)

Overaction and underaction of extraocular muscles were assessed by testing ductions and versions in all diagnostic positions of gaze. Oblique muscle dysfunction was graded on a scale from 0 to − 4 for SO underaction and from 0 to + 4 for inferior oblique (IO) overaction.(11) The Bielschowsky three-step test was performed for all patients. Primary inferior oblique overaction was differentiated from bilateral superior oblique palsy by the absence of primary position hypertropia and abnormal head posture. Moreover, the absence of superior oblique underaction on version testing was in favor of superior oblique muscle palsy. Finally, through the Bielschowsky three-step test, superior oblique muscle palsy was diagnosed with hypertropia in the primary position that increased in ipsilateral head tilt compared to contralateral tilt.(3, 5, 11) In young children, to confirm SOP, short-time unilateral patching was performed to look for correction of the head posture after patching.

The angle of deviation was measured by alternate prism cover test with the prism placed in front of the paretic eye in 6 gazes; 1 and 2: near (33 cm) and distance (6 m) in primary position, 3 and 4: ipsilateral and contralateral gaze, 5 and 6: ipsilateral and contralateral head tilt (30° head tilt to each side).

We used the following definitions in our study:

1. Unilateral SOP: This term was defined for patients with incomitant hypertropia, which increases on the contralateral gaze. The patients had positive Bielschowsky’s head-tilt test with unilateral SO underaction and /or inferior oblique (IO) overaction.

2. Bilateral SOP: These patients had both SO muscles underaction and/or overaction of both IO muscles in version test; associated with positive Bielschowsky’s head-tilt test on either side. There was also right hypertropia on the left gaze and left hypertropia on the right gaze.(11) Diagnosis of masked bilateral superior oblique palsy is established when signs of SOP appear in the normal eye of a patient who has undergone strabismus surgery for SOP in the contralateral eye.(1, 11)

3. Congenital SOP: was considered in patients with an onset of vertical strabismus or any abnormal head posture since early childhood either by history or old family photo albums, absence of diplopia, a large range of vertical fusion vergence or presence of commitancy e in vertical deviation. Patients may have a combination of these criteria.(12, 13)

4. Acquired SOP: These patients had a positive history of head trauma secondary to fall, car or motor accidents, any orbital/intracranial surgery, assault or ischemic etiology (e.g., hypertension and diabetic mellitus), which was considered significant enough to induce SOP.(13)

Primary inferior oblique overaction was differentiated from unilateral superior oblique palsy by the absence of head posture, no hypertropia in the primary position no superior oblique underaction on version testing and finally, through the Bielschowsky three-step test which in SOP, the hypertropia in the affected eye was increased in ipsilateral head tilt.(14, 15)

The data was analyzed using SPSS-version 24 software (IBM, Armonk, NY, USA). Normal data distribution was tested by Shapiro–Wilk and according to the normal distribution of the data, two-independent sample t-test was applied to determine statistically significant differences in some variables between congenital and acquired groups. Mann-Whitney test was applied to compare quantitative variables between congenital and acquired groups. χ2 was also used to evaluate the significant differences in quantitative variables such as gender and laterality in each group. The Wilcoxon test was performed to compare the parameters between the eye with superior oblique palsy and the normal eye and the mean angle of deviation in different gazes in patients with unilateral superior oblique palsy. P-values less than 0.05 are considered significant.

This historical cohort study was performed on 1057 patients with SOP who underwent surgery, including 557(52.7%) males and 500 (47.3%) females (P = 0.08) with a mean age of 21.7 ± 14.8 (range, 1–82) years. Unilateral SOP was observed in 990 (93.7%) patients, and 67 (6.4%) patients had bilateral involvement (P < .001).

Congenital and acquired etiologies were found in 764 (72.3%) and 293 (27.7%) patients, respectively (P < .001). The mean age of patients at the time of surgery was 17.4 ± 12.1 (range 1–58) years for congenital and 32.6 ± 15.6 (range 3–82) years for the acquired SOP group (P < .001).

Of 957 patients who had cooperation for measuring CVDA, the prevalence of amblyopia was 10% (n = 96) which was mild in 72 (75%), moderate in 17 (18%) and severe in 7 (7%) patients. The Mean preoperative vertical deviation in primary position was 14.6 ± 7.9 (range, 2–45) prism diopter (PD) at near and 15.4 ± 8.2 (range, 0–50) PD at distance. Vertical deviation in bilateral cases was significantly less than in unilateral cases in distance measurement (13.3 ± 9.1 vs 15.6 ± 8.3 PD, P < 0.001).

Of all SOP cases, 940 (88.9%) patients required only one procedure and 117 (11.1%) cases underwent two or more surgeries. Isolated inferior oblique myectomy was the most common first type of surgery in both unilateral (n = 756, 77.1%) and bilateral (n = 35, 52.2%) groups. Surgery was performed on the paretic superior oblique muscle in 42 (4.0%) patients alone or combined with other vertical muscles. Of 1057 SOP cases, horizontal strabismus (> 10 PD) was observed in 119 (11.3%), where 60 (5.7%) had it addressed in the first surgery, 55 (91%) for exotropia and 5 (9%) for esotropia.

A. Unilateral Superior Oblique Palsy

Unilateral SOP was found in 990 (93.7%) patients with a mean age of 21.8 ± 14.8 (range, 2–84) years and slightly higher prevalence in men (n = 525, 53.6%) and in the right eye (n = 518, 52.9%). The congenital and acquired etiologies of SOP in unilateral cases were observed in 715 (72.2%) and 275 (27.8%) patients (P < .001). The mean age of congenital and acquired unilateral SOP patients at the time of surgery was 17.7 ± 12.1 (range 1–58) and 32.7 ± 15.6 (range 3–82) years, respectively (P < 0.001). In the congenital group, 364 (50.9%) were males, and 351 (49.1%) were females (P = 0.627), but the frequency for males and females in acquired type was 163 (59.3%) and 112 (40.7%) patients, respectively (P = 0.02). In acquire SOP group, the mean duration between the onset of paresis and surgery was 3.8 ± 3.5 years (range, 6 months- 20 years).

Of 898 patients with Unilateral SOP who cooperated for measuring CVDA, the mean of CDVA in the affected eye and the other eye was 0.03 ± 0.11 and 0.04 ± .01 logMAR, respectively (P = 0.870). Of these patients, 727 (78.2%) had a complete vision (0 LogMAR) in both eyes and the prevalence of amblyopia was 9.9% (n = 89). The severity of amblyopia was mild in 67(75%), moderate in 15(17%) and severe in 7(8%) cases.

Information on the presence or absence of diplopia was recorded in 855 (272 acquired and 583 congenital) patients over five years old. Diplopia was reported in 148 (17.3%) of all unilateral patients. The frequency of diplopia in acquired cases (n = 88, 32.4%) was significantly higher than in congenital patients (n = 60, 10.3%) (P < 0.001).

In unilateral cases, 847 (85.6%) patients (578 congenital and 269 acquired) had abnormal head posture. Contralateral abnormal head posture was found in 835 (84.3%) patients (574 congenital and 261 acquired), and 12 (1.2%) patients (four congenital and eight acquired) had a paradoxical abnormal head posture. There was no report of AHP in the records of 143 (14.4%).

Remarkable Ipsilateral superior oblique underaction (≤ -2) was detected in 290 (27.4%), and Ipsilateral inferior oblique overaction ( ≥ + 2) was seen in 884 (83.6%) patients. The prevalence of oblique muscles dysfunctions in adduction in all congenital and acquired groups are shown in Table 1. The mean ipsilateral IO overaction in congenital unilateral SOP was significantly higher than acquired ones (2.0 ± 0.7 vs 1.8 ± 0.7, P = 0.02). However, the mean ipsilateral SO underaction in the congenital group did not have a significant difference with acquired unilateral SOP patients (2.3 ± 0.6 vs 2.2 ± 0.7, P = 0.570).

Table 1

The grading of ipsilateral overelevation and under depression in adduction in unilateral SOP patients.
		Group
		Congenital N = 764	Acquired N = 293	Total N = 1057
Over elevation in adduction	+ 1	123 (16.1%)	50 (17%)	173 (16.4%)
	+ 2	490 (64.1%)	187 (63.8%)	677 (64.0%)
	+ 3	142 (18.6%)	56 (19.1%)	198 (18.7%)
	+ 4	9 (1.2%)	0 (0.0%)	9 (0.9%)
Under depression in adduction	0	514 (67.3%)	202 (68.9%)	716 (67.7%)
	-1	29 (3.8%)	22 (7.5%)	51(4.8%)
	-2	179 (23.4%)	60 (20.5%)	239 (22.6%)
	-3	42 (5.5%)	9 (3.1%)	51 (4.8%)
	-4	0.0 (0.0%)	0.0 (0.0%)	0 (0.0%)
N, number

The mean hypertropia at distance in the congenital group was 15.6 ± 8.2 (range, 2–50) PD, and in the acquired group was 15.0 ± 8.6 (range, 2–50) PD (P = 0.342). At near it was 15.0 ± 7.8 PD (range, 2–50) for the congenital and 13.6 ± 8.0 (range, 2–45) PD for the acquired group (P = 0.03). In the unilateral group, 348 (35%) of 990 patients had horizontal deviation of more than 5 (range, 5–85) PD. The mean angle of ocular deviation in the unilateral SOP is shown in Table 2.

Table 2

the mean angle of deviation in different gaze positions in patients with unilateral SOP.
			Minimum (PD)	Maximum (PD)	Mean (PD)	P-value*
Primary position	Vertical deviation	Far	2.0	50.0	15.6 ± 8.2	P < 0.001
	Vertical deviation	Near	2.0	45.0	14.7 ± 7.9	P < 0.001
	Horizontal deviation	Far	0.0	86.0	9.6 ± 6.9	P < 0.001
	Horizontal deviation	Near	0.0	88.0	10.3 ± 7.3	P < 0.001
Lateral gazes	Vertical deviation	Ipsilateral	0.0	50.0	10.1 ± 8.2	P < 0.001
Lateral gazes	Vertical deviation	Contralateral	2.0	50.0	18.4 ± 9.8	P < 0.001
Head tilt	Vertical deviation	Ipsilateral	2.0	55.0	18.6 ± 9.5	P < 0.001
Head tilt	Vertical deviation	Contralateral	0.0	45.0	10.9 ± 8.2	P < 0.001
PD, prism diopter
*Wilcoxon Signed Ranks Test

Of 990 unilateral cases, 906(91.5%) patients required only one procedure and 84(8.5%) cases had two or more surgeries. The rate of amblyopia frequency was significantly higher in patients who needed two or more surgeries (n = 23, 27.4%) compared to patients who were managed with only one surgery (n = 66, 7.3%) (P < 0.001).

The most common surgical procedure planned was IO myectomy (n = 756, 76.4%) followed by ipsilateral superior rectus recession (n = 48, 4.8%), contralateral IR recession (n = 25, 2.5%) and ipsilateral IR resection (n = 10, 1.0%). Superior oblique tuck was performed for 18 (1.8%) patients. In 176 (17.8%) unilateral cases, surgery was planned for more than one vertical muscle in the first surgery due to a large amount of hypertropia (Table 4). Also, concurrent horizontal muscle surgeries were performed in the first surgery for 53(5.3%) patients. In patients with unilateral SOP, the mean angle of hypertropia in different gaze positions for each surgical plan are reported in Table 3.

Table 3

The mean angle of vertical deviation in different surgical plans in patients with unilateral superior oblique palsy.
	Ipsilateral gaze (PD)	Ipsilateral head tilt (PD)	Primary position (PD)		Contralateral head tilt (PD)	Contralateral gaze (PD)
	Ipsilateral gaze (PD)	Ipsilateral head tilt (PD)	Near	Far	Contralateral head tilt (PD)	Contralateral gaze (PD)
Isolated IO myectomy	9.8 ± 9.4	10.1 ± 7.3	13.9 ± 7.3	14.7 ± 7.5	18.7 ± 10.4	17.7 ± 9.3
IO myectomy plus ipsilateral SR recession	16.0 ± 11.1	19.4 ± 13.75	20.1 ± 12.4	21.3 ± 13.7	26.6 ± 16.05	26.96 ± 11.2
IO myectomy plus Contralateral IR recession	9.1 ± 11.2	9.6 ± 8.0	14.5 ± 7.5	15.2 ± 8.6	15.2 ± 10.6	16.3 ± 14.5
IO myectomy plus SO tuck	8.0 ± 2.5	11.0 ± 6.6	12.5 ± 9.0	13.1 ± 10.1	15.3 ± 11.4	22.0 ± 18.2
IO: inferior oblique, SR: superior rectus, SO: superior oblique, IR: inferior rectus

Comparisons between patients who were managed with one surgery and those needed two or more surgeries are shown in Table 4. As shown in this table, the mean angle of horizontal deviation at near and distance was significantly lower in cases who were managed with only one surgery (P = 0.002 and P = 0.014, respectively). Also, the CDVA difference between the two eyes was significantly higher in cases who needed more than one surgery (< 0.001).

Table 4

Evaluating the effective factors on the reoperating rate in unilateral SOP patients.
		Surgery times	Mean ± SD	Mean Difference	95% Confidence Interval of the Difference		P-value*
					Lower	Upper
Age (year)		One surgery	21.6 ± 14.7	-1.0	-3.8	1.8	0.492
		Two or more surgeries	22.6 ± 15.5
Vertical deviation (primary position, PD)	Far	One surgery	15.3 ± 8.2	-0.9	-3.0	1.3	0.433
		Two or more surgeries	16.2 ± 9.2
	Near	One surgery	14.4 ± 7.8	-1.4	-3.5	0.7	0.182
		Two or more surgeries	15.8 ± 8.5
Horizontal deviation (primary position, PD)	Near	One surgery	10.0 ± 6.3	-3.4	-5.5	-1.2	0.002
		Two or more surgeries	13.3 ± 12.4
	Far	One surgery	9.4 ± 5.9	-2.7	-4.8	-0.5	0.014
		Two or more surgeries	12.1 ± 13.0
CDVA difference between eyes (logMAR)		One surgery	0.03 ± 0.11	-0.057	-0.087	-0.026	< 0.001
		Two or more surgeries	0.09 ± 0.16
* Two-independent sample t-test

PD, prism diopter; CDVA, best-corrected distance visual acuity.

B. Bilateral Superior Oblique Palsy

Of 1057 patients, 67 (6.3%) cases had bilateral SOP, including 30 (45%) males and 37 (55%) females with a mean age of 19.4 ± 15.6 (range, 1–73) years. The congenital and acquired causes for bilateral cases were observed in 49 (73.1%) and 18 (26.9%) patients, respectively (P < .001). The mean age of patients with congenital and acquired bilateral SOP at the time of surgery was 12.4 ± 11.3 (range, 1–58) and 30.3 ± 8.0 (range, 22–53) years, respectively (P < 0.001). Eighteen (26.9%) of bilateral cases were diagnosed following the first surgery, as masked bilateral SOP, when hypertropia manifested in the contralateral eye. The mean CDVA in the right and left eye was 0.04 ± 0.11 (range 0.0–0.7) and 0.03 ± 0.08 (range 0.0–0.4) logMAR, respectively. In bilateral cases, amblyopia was detected in 7(10.4%) patients. Information on the presence or absence of diplopia had been recorded in 53 (18 acquired and 35 congenital) patients above five years of age. Diplopia was reported in 16 (23.9%) of all bilateral patients. The frequency of diplopia in acquired cases (n = 10, 55.5%) was significantly higher than in congenital patients (n = 6, 17.1%) (P < 0.001).

The mean angle of hypertropia at distance and near was 14.3 ± 9.1 (range 2–40) PD and 13.4 ± 8.3 (range 2–35) PD, respectively. Concurrent horizontal deviation (> 5 PD) was detected in 14(20.9%) of patients, 12.5 ± 10.4 (range 0–40) PD at near and 13.4 ± 8.3 (range 0–30) PD at distance. There were no significant differences between the mean amount of hypertropia in the right (12.9 ± 9.2 PD) and left (13.6 ± 9.8 PD) gazes (P = 0.66), as well as between right (14.5 ± 7.3 SD) and left (10.0 ± 6.5 PD) head tilts (P = 0.06).

(12)(52.2%) patients, followed by Harada-Ito procedure in 12 (17.8%) and bilateral IR recession in 4 (6.0%). Of 67 bilateral cases, 34 (51%) patients required only one procedure and 33(49%) needed two or more surgeries.

The clinical manifestations of SOP have been reviewed in a few studies.(5, 12, 15) Like most of them, we observed a predominance of disease in younger patients (mean, 21.7 ± 14.8 years). The mean age of patients in the present study is close to Van Noorden (24.7 years) and Bagheri et al (19.7 ± 11.7 years) studies.(1, 16) Same as previous studies,(16, 17) there was a preference for males (52.7% vs 47.3%), and compared to acquired causes for SOP, most of the patients were of congenital type (27.7% vs 72.3%). Ellis et al. study on 108 SOP patients showed that 76.9% of cases were congenital,(5) which is almost similar to our finding. Similar to the Ellis study, the congenital group in Bagheri et al. report was 76.7% of the total,(16) while in the study by Helveston et al. the congenital group constituted only 43.9% of the total.(18) This remarkable difference can be due to their small sample size (n = 82). We noticed that congenital SOP requiring surgery was twice as frequent as acquired SOP, raising the possibility that acquired SOP may have resolved more frequently, even spontaneously. The question arises whether the presence or absence of diplopia is a helpful symptom in distinguishing between acquired and congenital paralysis. Diplopia present more frequently in patients with recently acquired SOP; however, in the present study, nearly 11% of all congenital cases reported diplopia; therefore, it seems that the presence of diplopia cannot confirm the acquired cause, since patients with decompensated congenital SOP can also report diplopia.

Bilateral SOP was present in only 6.3% of our cohort. This is comparable with results from Mollan et al, who had 10 (6.6%) of bilateral palsy among 150 cases,(15) and slightly less than those in the study of Gunderson et al, who reported 12 (9.6%) bilateral cases among 124 SOP cases.(19) Prevalence of bilateral type should probably be higher than our reported value because most bilateral cases have an acquired origin and recover before surgery.

In the present study, amblyopia was detected in 9% of all patients who cooperated for visual acuity control, which was close to Holmes et al. study (7.5%).(20) While the prevalence of amblyopia in Bagheri et al.(16) and Tarczy-Hornoch et al,(21) studies reported 19% and 17%, respectively. Of course, the sample size in the current study is not comparable with the last two studies.

A head tilt toward the shoulder of the unparalyzed side is considered as a classic sign of unilateral involvement SOP but, it is not an exclusive sign of SOP and can be seen in other vertical muscles pathology or neurologic pathology.(11, 22) Head tilt was detected in a significant number of patients (85.6%) in the present study. The rate of head tilt in Merino Sanz study was reported 94.5%.(23) The absence of head tilts has been explained by the inability to obtain single binocular vision by any head position, or the presence of large fusional amplitudes or reduced visual acuity in one. Severe amblyopia may be one of the reasons, as was mentioned in Debaji Ray's study,(17) but in the present study, we were unable to reach this conclusion. If the head tilted toward the contralateral eye is not enough for overcoming the residual vertical deviation and diplopia, or if the fusion was only intermittent, some patients prefer to have a head posture that elicits double vision with wide image separation Therefore, some patients use of paradoxical head tilts to disrupt the fusion. The paradoxical head tilt was detected in 12 (1.2%%) of unilateral patients. In Debaji et al study, 2 of 181 SOP patients had the paradoxical head tilt with posttraumatic SOP with a large vertical deviation of more than 25 PD.(17) Khan et al reported a 1-year-old baby showing paradoxical diplopia in whom the paralytic eye was the fixating eye.(24) This report shows that paradoxical diplopia can be seen in both congenital and acquired types.

Some SOP patients present with concomitant horizontal deviation. In Merino Sanz study, 51.3% of patients had horizontal strabismus, mainly exotropia, in which, 6.6% required surgery.(23) Associated horizontal strabismus has been reported in 50–60% of SOP patients, both in congenital and in acquired type.(16, 25) Helveston et al. reported that 36% of SOP cases had concomitant horizontal deviation and 10% of them underwent combined horizontal surgery.(10) Based on some studies, horizontal rectus muscle surgery was mostly needed in horizontal deviations larger than 10 PD, since most of the lower amounts could be resolved after surgery for only cyclovertical muscles.(10, 16, 25) In our report, horizontal strabismus (> 10 PD) was detected in 119 (11.3%) patients, and only 60 (5.7%) of them were managed with appropriate horizontal muscle surgery.

The entity of the masked bilateral SOP has been described by Kushner,(26) where the hypertropia of the lesser affected eye, was not present in any field of gaze or in any head tilt. In the Kushner series, 9 of 28 (32%) bilateral cases had significant asymmetric involvement and masked type. Eighteen (26.9%) of 67 bilateral cases in the present study had similar presentation; Therefore, the examiner should be cautious about the possible involvement of the second eye, which may become manifest after surgery on the hypertropic eye.(26)

The various surgical procedures for the management of SOP were planned mostly based on the amount of the vertical deviation at the primary position, and the method chosen by the surgeon to correct the deviation. Some prefer operating on one muscle only for the first procedure to avoid overcorrections and waiting before planning a second intervention.(26)

Reports from different studies show that surgery for SOP is successful in 58–95% of cases.(16, 27, 28) However, older age, greater vertical and torsional deviations and amblyopia have been mentioned as predisposing factors for reoperation.(23, 29, 30) In the present study, the second surgery was performed for 117 (11.1%) of patients compared to 25% in Sanz et al study.(23) In the recently published cohort study by Heo et al., the reoperation rate for SOP was 10.7% which is close to our finding. In their study, patients who underwent surgery that included the superior oblique muscle or patients who had surgery on more than one vertical muscle (excluding superior oblique muscle) had increased hazard ratios for reoperation.(31) Significant horizontal deviation, the CDVA difference between eyes and the presence of amblyopia, were factors that increased the chance of needing two or more times surgery in the present study.

The retrospective nature of this study costed some limitations, including the unavailability of some data. We did not have reliable data about facial asymmetry or subjective or objective cyclotorsion in our patients. However, this study contains the weaknesses inherent to any retrospective, non-randomized study, including missing data and lack of standardized treatment plans across all cases.

The current study was to evaluate the clinical characteristics of 1057 subjects with SOP. Except for Heo et al. study,(31) other published articles regarding SOP, have a significantly small sample size compared present study. Albeit Heo et al(31) study was conducted using claims data that excluded the patients with acquired SOP and did not provide information on the angle of deviation, presence of abnormal head posture or visual acuity. The higher number of patients in this study, compared to previous studies, allows us to report the results of data analysis with greater accuracy. This study showed that congenital SOP underwent surgery twice as frequently as acquired SOP and most patients managed with only one procedure, with the inferior oblique muscle being the most frequent muscle operated on. Compared to previous studies, the current research has been focused more on patient refraction, visual acuity, and corrective surgical plans.

SOP

Superior Oblique muscle Palsy

Inferior Oblique

AHP

Abnormal Head Posture

Ethics approval and consent to participate

The ethical committee of Tehran university of medical sciences approved the protocol of this study (IR.TUMS.FNM.REC.1400.012) and this study adhered to the tenets of the Declaration of Helsinki and HIPAA. As it was a retrospective study, informed consent was waived by the ethical committee of Tehran University of Medical Sciences.

Consent for publication

Not applicable

Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no competing interests.

Funding

There was no special funder for this study and no financial disclosure for the authors.

Authors' contributions

Babak Masoomian, Masoud Khorrami-Nejad and Arash Mirmohammad Sadeghi contributed to the design and implementation of the research. Marrwan Hisham Mohammed, Motahhareh Sadeghi, Masoud Aghsaei Fard and Masoud Khorrami-Nejad analyzed the results and to the writing of the manuscript. Also Mohamad Reza Akbar read and approved the final manuscript.

Acknowledgements

Not applicable.

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No competing interests reported.

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Editorial decision: Major revision
23 Oct, 2023
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Superior Oblique Muscle Palsy: Clinical Characteristics and Surgical Approach in 1057 Patients

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Abstract

Background

Methods

Results

Conclusion

Trial registration:

Background

Methods

Result

A. Unilateral Superior Oblique Palsy

B. Bilateral Superior Oblique Palsy

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

Status:

Version 1