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Dr.Ankita, Prof.Kamlesh,Dr.Anju Rastogi,Dr.Shweta

ABSTRACT

PURPOSE :  To compare  the outcomes of hang-back and conventional recession of inferior oblique(IO) in V-pattern strabismus with inferior oblique overaction(IOOA).

METHODS :  A randomized control study with 50 patients of age 6 to 30 years having V-pattern strabismus with IOOA, divided equally into  groups A and B, underwent bilateral 10mm IO recession. Group A  by hang-back method and Group B by conventional  (park’s ) method.

RESULTS :The mean preoperative V pattern was  23.44±5.88 PD in group A and 24±5.77 PD in group B. The mean correction of V-pattern at 3 months follow upwas  18.32±6.01 PD  in group A and  19.80±5.99 PD  in group B.  The mean correction of IOOA  was 17.64±2.43 PD in group A and 18.12±3.12 PD in group B.Mean shift in extorsion was 3.08±1.8 in group A and 3.72±2.14 in group B.

CONCLUSIONS : Both the procedures are equally efficacious however hang-back recession being a safe and landmark free surgery,  can be an attractive alternative to conventional recession.

INTRODUCTION

Pattern strabismus has added a new dimension to the field of strabismology. It has been a subject of considerable research for the last few decades as it is difficult to manage as compared to concomitant horizontal deviations. Pattern strabismus is defined as vertical incomitance in horizontal deviation.1The etiology of A and V phenomena has evolved through various hypothesis and horizontal recti, vertical recti, the obliques and orbital factors have been held responsible for this phenomenon.2 The oblique muscle dysfunction has been the most popular theory till date.2,3

As the role of inferior oblique overaction(IOOA) was established in the etiopathogenesis of V pattern, the role of inferior oblique muscle weakening procedures came into play. 4,5,6Various procedures for inferior oblique weakening have been described like myotomy, myectomy at origin, denervation-extirpation, recession, pure antero-positioning and anteronasal transposition.7,8,9.10,11,12.13.14

Recession of the inferior oblique remains the most popular method as its superiority was proved by Park’s study in 1972 and has been theaccepted surgery worldwide.15Hang back recession is relatively a new, safe and effective entity for inferior oblique weakening, described by Kamlesh et al in 2007.16It is a landmark free surgery which requires minimal manipulation, thus taking a shorter surgical time. There is a paucity of study comparing the results of Hangback recession and conventional method of recession in V-pattern strabismus.

This study aims to compare the results of conventional and Hang-back recession of inferior oblique in patients with V pattern strabismus with inferior oblique over action in terms of their efficacy and complications.

MATERIALS AND METHODS

We conducted a prospective interventional randomized comparative study at a tertiary eye care centre. The study was approved by Institutional Ethics Committee and research adhered to the tenets of Declaration of Helsinki.50 patients in age group 6 to 35 yearswith significant V phenomena (i.e. At least 15 prism diopter difference between the upgaze and downgaze measurements) with IOOA were included in the study after taking informed consent. The exclusion criteria were, IOOA less than 10 prism diopters, history of any previous strabismus surgery, restrictive strabismus, neurological instability and presence of nystagmus or any fundal pathology.They were randomly assigned in two groups of 25 patients each.Group A underwent conventional method of recession while Group B underwent inferior oblique recession by Hangback method.

A detailed history was taken with emphasis on the age of onset of strabismus, progression, duration, deviation if constant or intermittent, asthenopic symptoms, diplopia, history of any previous treatment, amblyopia therapy or surgery and family history of squint. A thorough preoperative examination was done including unaided and best corrected visual acuity (BCVA) obtained after cycloplegic refraction,anomalous head posture,  measurement of horizontal and vertical deviation, Inferior oblique overaction, pattern, torsion and assessment of binocularity.

All patients underwent 10mm Inferior oblique recession in addition to horizontal muscle surgery as required. Patients were worked up for local or general anaesthesia as needed, The surgeries were performed by same surgeon. For local anaesthesia,  peribulbar block was given with 2% lignocaine and 0.5 % bupivacaine mixed with hyaluronidase. Success was defined as residual V pattern of less than 10 prism dioptersat 12 weeks post operative period for both the surgical procedures.

SURGICAL TECHNIQUE:

Group A underwent conventional recession of Inferior oblique by parks method while Group B patients underwent hangback recession of inferior oblique. Simultaneous horizontal rectus surgery was performed according to the amount of horizontal deviation in primary gaze.

Initial steps of the surgeries remain same in both the procedures. Traction sutures were applied. A fornix based conjunctival incision is made in the inferolateral quadrant 8 mm from the limbus and dissection of tenon’s capsule is performed to identify inferior oblique muscle, and the fascial attachments of the muscle are cut under direct visualization.

GROUP A: In the conventional recession by parks method, a double armed 6-0 vicryl suture was passed 3mm from the insertion of the inferior oblique muscle at the anterior border. The muscle was then severed from its insertion 3mm from the globe in order to ensure that there was no damage to the macula. The lateral end of the inferior rectus insertion was now visualized with minimum dissection. The anterior end of the inferior oblique was now attached 3mm inferior and 2mm lateral to this end of the inferior rectus. Horizontal muscle surgery was done at this time if needed and then the conjunctival incisions closed by 6-0 vicryl or silk.

GROUP B: In hang back recession method, a suture was passed 4 mm from the insertion site through the width of the inferior oblique muscle, with locking bites on both ends. The same suture was then passed proximally 2 mm from the insertion site in a loose fashion. In this way loops were formed between the proximal and distal suture bites on the inferior oblique muscle. The intermediate area between the two suture lines was then cut. The proximal part of the severed muscle is then suspended from the distal muscle. The amount of recession to be performed is then measured on both arms of the polyglactin 910 suture. While the surgeon holds the suture with the help of smooth forceps, the proximal ends of the suture are tied. The proximal portion of the muscle is allowed to retract into its sheath and is expected to stay recessed according to the amount of recession, preserving the normal course of the muscle.

Patients were prescribed steroid and antibiotic eye drops 6 hourly along with a lubricant. Post operative follow-up was done at day 1, 1 week, 1 month and 3 months and results were recorded. The post operative follow up included assessment of visual acuity, horizontal alignment, measurement of V pattern and  IOOA , binocularity, torsion and complications if any.

STATISTICAL ANALYSIS

Quantitative variables were compared using Independent T test/Mann-Whitney Test (when the data sets were not normally distributed) between the two groups.Qualitative variables were compared using Chi-Square test/Fisher exact test. A p value of <0.05 was considered statistically significant.

RESULTS

50 patients divided in two groups of 25 each were operated and followed up for a minimum of 3 months.The mean age was 13 ± 6.12 years in group A while the mean age in group B was 12.92 ± 6.62 years with a range of 6 to 30 years. V esotropias presented at an earlier age than V exotropias.

In Group A, the LogMar BCVA was 0.22 ± 0.24 in right eye  and  0.2 ± 0.25  in left eye. In Group B,theLogMar BCVA in right eye was 0.12 ± 0.19 and in left eye it was 0.14 ± 0.16. The best corrected visual acuity remain unchanged after the squint surgery till three months follow up. Refractive error was noted in 31 individuals out of which 19 (38%) were hyperopes and 12 (24%) were myopes. Rest of the patients (38%) were emmetropic. It can be inferred from the results of our study that the prevalence of hypermetropia was more in esotropes and myopia more in exotropes.

The prevalence of amblyopia in our study was 16% either unilateral or bilateral. 90% of amblyopic patients were esotropic pre-operatively. This could be because of early onset of deviation in esotropes leading to strabismic amblyopia. Early age of onset of deviation and uncorrected refractive error lead to more prevalence of bilateral amlyopia overall and in esotropes in our study.

Refractive errors can paly a role in development of misalignment of eye because of their effect on accommodation. Hypermetropes because of poor near vision put more accommodative effort in order to see a near object clearly which leads to convergent squint. Similarly, myopes use less than normal accommodative convergence because of good near vision. This constant understimulation of convergence may cause a divergent squint.

Preoperatively, out of 50 patients 27 (54%) were esotropic and 23 (46%) were exotropic. Postoperatively  36 (72%)  patients were orthotropic after the first surgery, 17 in group A and 19 in group B.Out of these 16 patients who remained esotropic or exotropic, 10 patients were within 10 PD of orthotropia which was considered as success criteria. Only 6 patients had residual deviation in primary gaze. There were no cases of consecutive esotropia or exotropia.

Preoperative mean V pattern in group A was24  ± 5.4 PD  while in group B was 23.44 ± 6.44 PD.  Postoperative mean V pattern in group A was 3.32 ± 3.52 PD at 1 week, 3.96 ± 3.35 PD at 1 month and 4.2 ± 3.51 PD at 3 months. The postoperative mean V pattern in group B was 4.24 ± 4.25 PD at 1 week ,  5.12 ± 4.08 PD at 1 month and 5.76 ± 3.8 PD at 3 months. The mean reduction in V pattern in group A was 20 ± 6.78 PD while in group Bwas 18.2 ± 5.48 PD at 3 months follow up. The difference was statistically significant(p= 0.041)

IOOA was graded on a scale of 1+ to + 4 on the basis of amount of overelevation in adduction.

The pre operative average IOOA in group A was 19.12 ± 3.29 PD in right eye and 18.92 ± 3.51 PD in left eye, in group B was 18.28 ± 3.17 PD in right eye and 17.68 ± 2.73 PD in left eye.

The postoperative IOOA in group A was 0.64 ± 2.33 PD at 3 months in right eye and 0.8 ± 2.55 PD in left eye.

In group B, the postoperative IOOA was 1.76 ± 1.38 PD at 3 months in right eye and 2.08 ± 1.53 PD in left eye. The reduction in IOOA in group A was 18.48 ± 3.13 PD while in group B the reduction in IOOA was 16 ± 2.93   PD at 3 months follow up which was statistically significant.

The mean preoperative deviation in primary gaze in group A was 45.6 ±11.67 PD while in group B it was 47.6± 6.47PD. Postoperatively, the mean deviation in primary gaze at 1 week was 3.92± 6.97 PD in group A and 3.16 ±4.54 PD in group B. At 3 months the mean postoperative deviation in primary gaze 3.92 ± 6.97 PD in group A and 3.4 ± 4.85 PD in group B.

Preoperatively, 92 % patients had extorsion as measured by their fundus photograph. No subject had intorsion. The average torsion (actually Disc Foveal Angle) in group A was 18.52 ± 3.95 degrees in right eye and 17.64 ± 3.38 degrees in left eye. In group B the values were 18.4 ± 3.87 degrees in right eye and 18.32 ± 4.63 degrees in left eye.

The post operative torsion at 3 months in group A was 14.12 ± 2.74 degrees in right eye and 13.28   ± 2.49 degrees in left eye.  In group B post operative torsion at 3 months was 13.6 ± 2.36 degrees in right eye and 13.8   ± 3.24 degrees in left eye. The reduction in torsion in group A was 4.0 ±1.47 degrees while in group B it was 3.6 ± 1.96 degrees at 3 months follow up.

10 % (5) patients developed grade 2 binocularity post-operatively, 2 in group A and 3 in group B while only 1 patient showed stereopsis for near after surgery. It was observed that early age at surgery and short duration between onset of strabismus and surgery favoured the development of binocularity.

There were no cases of consecutive esotropias or exotropias. There were no cases of scleral perforation or snaring of tenon’s capsule. No limitation of elevation was seen in any case postoperatively.

Discussion

The pathogenesis , evaluation and management of pattern strabismus has developed through various stages and still remains a challenging situation. The surgical approach depends on the amount of inferior oblique overaction which is identified by over-elevation in adduction. Moderate amount of IOOA can be corrected by recession which has been the most preferred method of inferior oblique weakening.However conventional recession requires extensive dissection for identification of muscle insertion and the muscle is sutured to the new insertion point in relation to inferior rectus or lateral rectus. The procedure of intrascleral suturing becomes difficult in children, high myopes and  cases with scleral thinning. The risk of inadvertent scleral perforation and snaring of tenon’s capsule becomes higher especially with inexperienced surgeons. Also it is difficult to adjust the sutures post operatively if required. Hangback recession theoretically eliminates these problems but the efficacy of this relatively new procedure has been questioned in the past. This study was conducted to compare the two methods of inferior oblique recession in terms of their efficacy and complications..

We compared the reduction in V pattern and the post operative drift in the two groups. The mean preoperative V pattern was 23.44±5.88 PD in group A and 24±5.77 PD in group B. The correction of V-pattern with mean follow up of 1 year was  18.32±6.01 PD  in group A and  19.80±5.99 PD  in group B.  The correction of IOOA  was 17.64±2.43 PD in group A and 18.12±3.12 PD in group B.

The mean reduction in V pattern by conventional recession as reported by Kamlesh et al  was26.9 PD . In V exotropes , reduction was 25.83 PD and in V esotropes reduction was 19.75 PD. The only study available on hangback recession by Kamlesh et al reported a correction of 19 ± 2 PD in V-exotropia group and 22 ± 7 PD in V-esotropia group. Other studies on conventional recession have showed similar results. Burian obtained an average correction of 15.4 PD in V-esotropia and 11.4 PD in V-exotropia after bilateral inferior oblique recessions.17  Prem Prakash et al obtained a correction of 11 PD in V-exotropia and 9 PD in V-esotropia.18 We obtained a satisfactory outcome defined as V pattern less than 10 PD in 94 % of our cases.

The reduction in V-pattern was also more in esotropes except in group B exotropes. However, the difference was not statistically significant (P value : 0.546) (name of the test). Earlier studies by Kamlesh et al reported  more amount of reduction of V-pattern in exotropic patients while another study by Kamlesh et alon Hangback recession showed more reduction in esotropic patients.16,19

The shift in torsion between the two groups were comparable. Extorsion was corrected markedly at 3 months follow up postoperatively in both the groups.20

We also analyzed the post operative drift in alignment and V pattern seen at 3 months post-operatively. No significant difference in alignment was seen in primary gaze between 1week post and 3 months post operative period between the two groups .The V pattern at 3 months post operative was slightly more as compared to 1 week postoperative values. Hence, the reduction in V-pattern showed a decreasing trend over 3 months but the data was not statistically significant (p =0.873). Study by Park showed that the inferior oblique overaction reoccurred over 2 years.The mean V pattern showed an increasing trend from 1 week to 12 weeks postoperatively however the difference was not statistically significant. (which test was done) (P-value : 0.98)15

The difference between the two groups was not statistically significant The attainment of binocularity was dependent on the age of onset of strabismus and the age at the time of surgery.

We conclude that the outcomes of both the procedures are comparable, however, hangback recession has some additional advantages being a landmark free surgery with minimal manipulation eliminates the need for intrascleral suturing, thereby reducing the risk of inadvertent scleral perforation and snaring of tenon’s capsule. It is a relatively easier method taking shorter surgical time with reduced post operative congestion and discomfort. It may be preferred in children where the working space is lesser and the scleral rigidity is low. It also offers a theoretical advantage of intra- or post-operative adjustment of the inferior oblique muscle.

Since the site of attachment is not fixed in Hangback recession, the results can vary in different patients making it a less predictable procedure as compared to conventional recession. The width of the muscle might not be maintained as bulking of the muscle occurs in hangback procedures.

Hang-back recession of inferior oblique may be considered as a method of choice in patients of V-pattern strabismus with moderate amount of inferior oblique overaction.

However, this study has limitation of small sample size and relatively short duration of follow up. Prospective study with longer follow up and larger sample size may be required for comparing the outcomes and complications (including post-operative drift) of hang-back recession of inferior oblique with conventional recession.

REFERENCES

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