a prospective clinical trial was conducted on a consecutive series of the patients with primary io overaction or secondary overaction due to superior oblique palsy .
institutional review board approval was obtained and signed informed consent was obtained from all participants in accordance with the declaration of helsinki .
exclusion criteria included presence of dvd , history of simultaneous or previous strabismus and/or ocular surgery , inadequate follow  up , and concurrent conditions that might influence results such as eyelid anomalies and orbital disease .
the patients who did not cooperate enough for taking measurements were also excluded such as small children and the patients with low vision who could not fixate properly .
all patients received a thorough ophthalmic examination 1 day before surgery and 3 months thereafter .
overaction of io was determined as overelevation in adduction and graded by a scale ranging from 0 to + 4 .
output measurements were consisted of pf , margin reflex distance ( mrd ) 12 , lower lid function ( llf ) , hertel value , and lower lid crease ( llc ) .
pf was measured by assessing the distance between the upper and lower eyelid margin at the point that bisected the light reflex on the cornea .
mrd-1 represented the distance from the corneal light reflex to the upper eyelid margin whereas mrd-2 represented the distance to lower eyelid margin .
llf was assessed by measuring eyelid excursion from extreme upgaze to extreme downgaze while holding the head still .
hertel mirror exophthalmometer was used to measure the protrusion of the glob from the lateral orbital rim .
all the stable measurements were taken by a handheld ruler while the patient sitting upright and fixating with that eye to a penlight held at 50 cm in front of the patient .
all preoperative and postoperative measurements were always performed by the same examiner , who did not know the details of patients . to increase the reliability of the measurements , all were taken twice and the average value used , if there was any inconsistency a third measurement was considered .
the hyperdeviation was measured with prism and cover test or with krimsky test if corrected visual acuity was inadequate for prism and cover test .
all preoperative and postoperative examinations and measurements were made by the same observer , who was not masked to the data .
all surgeries were done using a similar technique which was first described by elliot and nankin . in this original procedure
, io was sutured just anterior to the insertion of the inferior rectus muscle ; however , we sutured the io posterior to the inferior rectus insertion .
in brief , a lid speculum was inserted and the globe was maximally elevated and adducted .
polyglactin 6 - 0 sutures were placed in the io near its insertion , with locking bites on either edge .
then , the muscle was freed and the anterior arm of the suture was placed posterior to the temporal edge of the inferior rectus muscle insertion .
the posterior arm was placed temporally and posteriorly within 23 mm [ fig . 1 ] .
hence , the new direction of the io insertion was also different from the original procedure of elliot and nankin . in original technique , the new io insertion should be just anterior but parallel to the inferior rectus insertion .
the anterior arm of disinserted inferior oblique muscle placed 12 mm posterior to lateral edge of inferior rectus insertion .
the posterior arm was placed temporally and posteriorly within 23 mm to anterior arm the differences of the collected data were calculated for statistical significance using the wilcoxon test .
all surgeries were done using a similar technique which was first described by elliot and nankin . in this original procedure , io was sutured just anterior to the insertion of the inferior rectus muscle ; however , we sutured the io posterior to the inferior rectus insertion . in brief , a lid speculum was inserted and the globe was maximally elevated and adducted .
polyglactin 6 - 0 sutures were placed in the io near its insertion , with locking bites on either edge .
then , the muscle was freed and the anterior arm of the suture was placed posterior to the temporal edge of the inferior rectus muscle insertion .
the posterior arm was placed temporally and posteriorly within 23 mm [ fig . 1 ] .
hence , the new direction of the io insertion was also different from the original procedure of elliot and nankin . in original technique , the new io insertion should be just anterior but parallel to the inferior rectus insertion .
the anterior arm of disinserted inferior oblique muscle placed 12 mm posterior to lateral edge of inferior rectus insertion .
the differences of the collected data were calculated for statistical significance using the wilcoxon test .
a total of 19 eyes of 16 consecutive patients who met the criteria were included .
the mean age of the patients was 8.7  7.1 years , with a range of 223 years .
seven eyes ( 36.8% ) of 4 cases had primary io overaction , while 12 eyes ( 63.2% ) of 12 cases had secondary overaction due to superior oblique palsy .
the surgery was performed unilaterally for one case with bilateral asymmetric primary io overaction because this case had severe amblyopia in that eye .
the median preoperative grade of io overaction was 3.5 ( ranging from 3 to 4 ) , which decreased to 0 ( ranging from 0 to 2 ) ( p < 0.05 ) 3 months postoperatively .
all of the eyes underwent anterior transposition of io placed 12 mm posterior to inferior rectus insertion .
the mean preoperative hypertropia in the primary position was 14.1  5.9 prism diopters ( pds ) and the mean postoperative hypertropia was 2.4  4.5 pd at the 3-month follow - up visit ( p = 0.005 ) .
demographic and operative data for patients who underwent anterior transposition of the inferior oblique the mean preoperative pf was 10.2  1.3 mm in which no change was observed and it was 10.2  0.9 mm postoperatively ( p = 0.79 ) .
the mean preoperative mrd-1 was 4.7  0.7 mm , which decreased postoperatively to 4.2  0.6 mm ( p = 0.08 ) .
the mean preoperative mrd-2 was 5.6  0.8 mm , which increased postoperatively to 5.8  0.5 mm ( p = 0.25 ) .
the mean preoperative hertel value was 15.4  2.2 mm which decreased postoperatively to 15.0  2.8 mm ( p = 0.48 ) .
the mean preoperative llf was 5.4  1.4 mm , which increased postoperatively to 5.6  1.2 mm ( p = 0.21 ) .
the mean preoperative llc was 4.6  1.2 mm which decreased postoperatively to 4.4  1.3 mm ( p = 0.41 ) [ table 2 ] .
preoperative and postoperative values of output measures abnormal head posture was observed in 12 patients and all of them had unilateral superior oblique palsy .
the abnormal head posture was not noticable in 7 ( 58.3% ) of these patients and the angle of head tilt reduced in 5 patients ( 41.7% ) at the 3-month postoperative visit .
within the orbit , a complex musculofibroelastic structure suspends the globe , interrelates with the eyelids , and other orbital elements .
the capsulopalpebral fascia which is analogs to the levator aponeurosis in the upper lid is a major component of lower lid retractors .
it originates from the belly of the inferior rectus muscle ; there are firm adhesions between capsulopalpebral fascia and inferior rectus . the capsulopalpebral fascia splits open and forms a anterior layer and a posterior layer which wrapping around the io .
any procedure on io as well as anterior transposition surgery might have effect on lower lid retractors and therefore might influence lower lid configuration and functioning .
anterior transposition of the inferior io , introduced by elliott and nankin , was highly effective in the treatment of dvd , primary inferior io overaction and secondary overaction due to superior oblique palsy .
we also observed clinically and statistically significant decrease in the preoperative hypertropia after this procedure and 68.4% of the patients achieved a hypertropia of 5 pd or less postoperatively .
anterior transposition has been shown to work in part by converting the io from an elevator to a depressor of the globe because the neurovascular bundle became a new origin for the temporal portion of the io .
elliott and nankin also found that anterior transposition of io was advantageous when compared to standard recession surgery and also was devoid of difficulties and complications related to reinserting the muscle .
graded anterior transposition  to reduce the complication of limited elevation . in this procedure , the amount of anterior transposition was titrated to the amount of io overaction .
farvardin et al . , reported combined resection and anterior transposition of io in the treatment of io overaction secondary to superior oblique palsy with successful results .
fard described anterior and nasal transposition of io for the treatment of dvd associated with io overaction .
limitation of elevation in abduction and/or adduction and hypotropia in primary position are known complications of anterior transposition surgery of io .
functionally , less significant complications such as pf alteration , pf asymmetry , lower lid fullness , were noted in a few study . in the present study ,
we prospectively evaluated the alteration of the pf , lower lid contour , and function parameters with anterior transposition of the inferior io surgery .
for this purpose , the pf , mrd-1 , mrd-2 , hertel value , llf , and llc were evaluated however , none of them revealed significant change postoperatively ( p > 0.05 ) .
comparable to our results , no postoperative pf asymmetry has been reported by goldchmit et al .
, after io anterior transposition in patients with unilateral io overaction . in their technique ,
the disinserted io was sutured adjacent to the lateral end of inferior rectus insertion bunched with one suture .
they noted slight lower lid curvature deformity on forced upgaze in four of ten patients .
farvardin and nazarpoor have observed mild fullness in 25% of the patients with superior oblique palsy following anterior transposition surgery in which the disinserted io was sutured just anterior to the lateral of inferior rectus insertion .
however , they did not reported any elevation of lower lid on upgaze in their patients .
however , kushner has mentioned that anterior transposition of the inferior io caused a narrowing of the pf and this could be cosmetically noticeable .
he compared postoperative pf of patients who underwent io transposition surgery with control group who underwent standard recession without transposition . in this work ,
the outcomes of transposition surgery were evaluated in two separate groups in first group the io was placed at the level of inferior rectus insertion and in second group the io was placed 2 mm anterior to inferior rectus insertion . compared with the control both groups showed significant decrease in pf and
gonzlez and cinciripini reported elevation deficiency , elevation of lower lid on upgaze and reduced inferior scleral show in the eyes following anterior transposition in which io reinserted 3 mm posterior from the limbus in the line of lateral edge of inferior rectus insertion .
they speculated that the reason for lower lid elevation to be the advancement of the capsulopalpebral fascia extending to inferior rectus .
some studies have reported that io transposition of 1 mm or more anterior to the inferior rectus muscle insertion as well as the lateral spreading of the posterior fibers more than 2 mm at the new insertion are risk factors for complications of this surgery such as anti - elevation syndrome and hypotropia . the lower lid elevation and fullness in lower lid on upgaze also noted more in this augmented anteriorization procedures .
kushner demonstrated that if the posterior fibers of io are inserted more distant from the lateral extremity of the inferior rectus insertion , the effect on limitation of elevation would be greater , because these new fibers become more stretched .
those cases can not be compared with ours because we performed anteriorization surgery in which io was placed posterior to the lateral end of the inferior rectus insertion thus , the posterior fibers had minor anteriorization .
postoperatively no significant change on lower lid configuration and function parameters were observed in our patients .
the small sample size and the parameters depending on patients cooperation such as pf , llf are main limitations of this study .
we tried to overcome this issue by including only cooperative patients and using the average of two compatible measurements .
due to close anatomic relationship of io with lower lid retractors , it is rational to expect an alteration of lower lid configuration and functioning with io surgery . in this study
, we did not observe any significant effect on lower lid parameters with io anterior transposition in which we placed the io posterior to inferior rectus insertion .
however , the alteration of these parameters might be more noticeable particularly in patients with greater degrees of anterior transpositions in which io placed anterior to inferior rectus insertion . placing the io posterior to the inferior rectus insertion avoiding further anterior transposition may enable successful surgical outcomes without any effect on eyelid configuration and functioning .
further observations should also be done on a larger number of patients to confirm the effect of io anterior transposition on the eyelid tissues .
 purpose : to evaluate the alteration of lower lid configuration and function with anterior transposition surgery of the inferior oblique ( io ) muscle.patients and methods : a prospective clinical trial was conducted on a consecutive series of patients underwent anterior transposition of the io as a sole operation . 
 all patients received a thorough ophthalmic examination 1 day before and 3 months after surgery . 
 output parameters were consisted of palpebral fissure , margin reflex distance 12 , lower lid function , hertel value , and lower lid crease . 
 the differences of the collected data were calculated for statistical significance by using the wilcoxon test.results:a total of 19 eyes of 16 consecutive patients were included . 
 the median preoperative grade of io overaction was 3.5 ( ranging from 3 to 4 ) , which decreased to 0 ( ranging from 0 to 2 ) postoperatively ( p < 0.05 ) . 
 no significant change was observed in all parameters 3 months postoperatively ( p > 0.05).conclusion : in this study , no significant effect on lower lid configuration and function was observed following io anterior transposition in which the disinserted muscle was placed posterior to inferior rectus insertion . 
Patients and Methods
Surgical technique
Statistical analysis
Results
Discussion
Conclusion
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Conflicts of interest