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infantile esotropia ( ie ) is one of the most common forms of pediatric strabismus , with a birth prevalence of 25 per 10,000 newborns.1 ie is a large , constant , stable angle esotropia with an onset within the first 6 months of life.2 features associated with ie include alternating esotropia , cross fixation , manifest - latent nystagmus , overacting inferior obliques , dissociated vertical deviation ( dvd ) , and reduced binocular vision.3 the final scope of treatment of ie is to align the visual axes to guarantee the development of binocular vision .
the focal point of this treatment is surgical intervention.4 nevertheless , due to the lack of randomized trials comparing different surgical strategies for ie , the most effective one and the optimal timing have not yet been univocally defined.3 according to scientific literature , surgical alignment of eyes in ie has a variable success rate reported to be from 45% to 80%;5 nevertheless , there are still few data regarding risk factors associated with the need of reoperation .
the aim of this study was to identify clinical and demographic factors associated with misalignment after first surgery in ie patients and reoperation rate .
a retrospective study was carried out analyzing data from 863 patients , examined and operated between 1980 and 2014 by the same surgeon ( am ) in the department of ophthalmology of  federico ii  university of naples , in the department of ophthalmology , orthoptics and pediatric ophthalmology of university of salerno , and in two other private centers .
this study was conducted in accordance with the declaration of helsinki and was approved by the institutional review board of the university of salerno . written informed consent was obtained from the parents / guardians of all patients .
the study inclusion criteria are the following : 
 confirmed ie diagnosis;strabismus angle 30 prism diopter ( pd);ie onset by the first 6 months of age;absence of central nervous system anomalies and ocular diseases;absence of hypermetropia over 3 diopters preoperatively;never undergone previous extraocular muscle surgery at the time of examination . confirmed ie diagnosis ; strabismus angle 30 prism diopter ( pd ) ; ie onset by the first 6 months of age ; absence of central nervous system anomalies and ocular diseases ; absence of hypermetropia over 3 diopters preoperatively ; never undergone previous extraocular muscle surgery at the time of examination . to avoid heterogeneity in surgical approach , we selected patients who underwent bilateral medial recti recession ( oo rec mr ) , bilateral lateral recti resection ( oo rec lr ) , and inferior oblique recession and anteroposition ( o rec - ap io ) .
all patients underwent a preoperative assessment evaluating : sex , familiarity for strabismus , entity of the angle of deviation at nearby krimsky test ( estimated after the total correction of the refractive defect when present ) , antiamblyopic occlusion therapy , optical correction , lateral recti hypofunction , hypertropia , alphabetical variations ( v or a variations ) , dvd , nystagmus , anomalous head positions , amblyopia , and cross fixation .
we divided our sample into groups based on the amount of deviation : group 1 ( 3040 pd ) , group 2 ( 4159 pd ) , and group 3 ( 60 pd ) .
as the presence of upshoot fell within our inclusion criteria , we considered as a discriminating factor the uni- or bilaterality and the symmetry of it . in children with bilateral symmetric upshoot ,
the same entity of recession with anteroposition of inferior oblique was performed in both eyes , while asymmetric upshoot required a different entity of recession and anteroposition in the two eyes .
therefore , we evaluated the number of those patients in whom upshoot was not either bilateral and/or symmetric in order to consider the possible different rate of unsuccessful surgery .
furthermore , we divided our sample into three intervals , according to the age at time of surgery : within the 2 years of life , between 2 and 3 years , and over 3 years ( before age 5 ) .
considering the surgical strategy , two main parameters were examined : timing and associated conjunctival recession ( performed or not performed ) .
postoperative evaluation included assessment of motor alignment approximately at 3 months , 6 months , 1 year , and 5 years .
motor alignment was categorized as  adequate  if alignment was within 10 pd ( deviation > 0 and 10 pd or deviation < 0 and 10 pd ) after a single intervention , or  unsuccessful  if deviation was 10 pd or 10 pd .
the same surgeon ( am ) decided when reoperation was needed , considering the following criteria : significant residual esotropia or secondary exotropia with a measurable angle > 10 pd reported during different postoperative examinations not influenced by optical correction , sensory state evaluation , appropriate angle follow - up showing angle stability and allowing to give surgical indications , and presence of dvd .
statistical analysis was performed with a logistical regression model in which the dependent variable was the presence / absence of reoperation , while the predictors have been selected using a forward type model .
esotropia angle before surgery had a range from 30 to 40 pd in 144 children ( 27.43% ) , 41 to 59 pd in 204 patients ( 38.85% ) , and was > 60 pd in 177 ( 33.71% ) .
all children presented constant esodeviation at two consecutive examinations prior to surgery . in all , 194 children ( 36.95 % ) were operated before the age of 2 years , 228 ( 43.43% ) between 2 and 3 years , and 103 ( 19.61% ) after 3 years . conjunctival recession was performed in 65.3% of cases .
none of the children missed the 3-month postoperative visit , while 17 ( 3.2% ) , 34 ( 6.5% ) , and 117 ( 22.3% ) missed the 6-month , 1-year , and 5-year postoperative visit .
the percentage of patients lost at follow - up considerably increased 5 years after surgery .
adequate alignment ( within 10 pd of orthotropia ) was achieved for 71.2% to 81.3% of children at the 3-month , 6-month , 1-year , and 5-year postoperative visit ( table 2 ) .
regarding reoperation , 50 children ( 9.52% ) underwent additional surgery at 2.93 years after the first operation , at a mean age of 6.54 years .
fourteen reoperations were performed in group 1 , 17 reoperations in group 2 , while 19 second surgeries were recorded in group 3 .
a total of 35 children needed additional surgery for consecutive exotropia while 15 for residual esotropia . concerning statistical analysis , in a multiple - variable logistic regression model , older age and family history of strabismus
were associated with an increased probability of reoperation , while male sex and hypertropia were associated with a decreased probability of reoperation ( table 3 ) .
antiamblyopic occlusion therapy , optical correction , lateral recti hypofunction , alphabetical variations ( v or a variations ) , absence of bilateral symmetric upshoot , dvd , nystagmus , anomalous head positions , amblyopia , and cross fixation were not associated with reoperation .
although reoperation is one of the most common complications of ie surgery , only a few studies have identified factors associated with unsuccessful postoperative motor alignment .
the timing of initial surgery is one of the most important clinical factors associated with motor and sensory outcome .
our study confirms , as reported by recent studies,6,7 that surgery performed after the age of 3 years increases the risk of unsuccessful alignment at first operation ; in fact , children operated after 3 years of age have a significant increase of risk of reoperation ( odds ratio [ or ] 5.4 ; p<0.001 ) . instead
, surgery performed between 2 and 3 years of life is not significantly associated with a higher risk of need of reoperation compared with surgery performed before 2 years old ( or 1.616 ; p=0.230 ) .
our results are coherent with other studies that indicate late surgery as cause of unsatisfactory motor outcome.69 another important parameter to be considered is stereopsis .
as suggested by other studies,6,7 ie patients who are operated late generally achieve worse stereopsis , resulting in poorer motor alignment .
the current study does not investigate the long - term prevalence of stereopsis after surgery .
however , we have evaluated sensory postoperative outcomes in another in - press study on a similar ie patient cohort .
the data by our multivariate analysis report that children operated after 2 years of age were 0.4 times less likely to obtain binocular single vision ( bsv ) compared with children operated before 2 years of age ( adjusted odds ratio [ aor ] 0.38 , 95% confidence interval 0.170.89 , p=0.025).10 accordingly , several clinical studies showed that surgical realignment of the eyes during the first 2 years of life is associated with better sensory outcome than surgical alignment performed after 2 years of life.11,12 while in north america there is a tendency to perform surgery for ie usually before 12 months of life ( early surgery ) , in europe it is more often delayed till 1236 months ( standard surgery ) . in our practice , we do not operate children before 11 months due to the higher frequency of reoperation documented for early surgery.13 according to our data , inferior oblique hyperfunction evaluation is rarely accurate in very small children .
furthermore , potentially incomplete amblyopia treatment , angle instability , and delayed maturation of sensorimotor system , and possibility of at least partially spontaneous resolution justify our choice . in our study , 50 ( 9.52% ) children had a reoperation .
a reoperation rate of 34% was found by trigler and siatkowski,14 16%21% by foster et al,15 28% by maruo et al,16 and 20% by teller et al.17 in the  early versus late infantile strabismus surgery study,13 patients in an early - surgery cohort had 1.18 surgeries per patient compared with 0.99 surgeries per patient in late - surgery cohort .
simonsz and eijkemans,18 in a recent and detailed study , analyzed the rate of reoperation and rate of spontaneous resolution in ie .
the meta - regression analysis , including 12 studies , has shown reoperations rates between 60% and 80% for children first operated approximately at 1 year of age and ~25% for children operated around at 4 years of age .
the authors conclude accordingly that the benefit of early surgery for gross binocular vision is balanced by a higher reoperation rate . concerning the operation type , comparing our experience with literature data
, we can state that the surgical approach of bilateral medial recti recession , bilateral lateral recti resection , and inferior obliqui recession and anteroposition guarantee a good surgical result.19 another factor to evaluate is the role of family history of strabismus in ie . in the literature , frequency of family history of strabismus
is reported to be between 6% and 74%.13,14,20 in our patient cohort , the percentage of positive family history of strabismus is relatively low ( 9.9% ) .
our statistical model shows a higher risk of unsuccessful motor alignment at first surgery in children with a family history for strabismus ( or 2.4 ; p=0.042 ) .
we can speculate about the existence of genetically determined strabismogenic factors influencing both development of strabismus and treatment failure .
unlike previous studies , we found a lower risk of reoperation in male sex ( or 0.37 ; p=0.003 ) . in our sample ,
the percentage of male sex in the group of children requiring just one operation is 61% while it is 40% in the group of children who underwent reoperation .
trigler and siatkowski14 found a similar frequency of male sex , 55% in the group requiring only one operation , 45% in the group requiring two or more operations , but the difference was not statistically significant .
presence of hypertropia at presurgical evaluations affects motor outcome determining a significant lower risk of reoperation ( or 0.27 ; p=0.025 ) .
this finding is probably justified by the fact that in some children hypertropia may appear at a later stage , after the first intervention has been performed .
our study is not sufficient to provide data about the time of presentation of motor defects and relate the latter to the effect on treatment outcome .
smaller preoperative angles are usually associated with a favorable motor outcome.14 in contrast with this study , we found that the entity of preoperative angle does not affect the risk of reoperation .
deviation variability , antiamblyopic occlusion therapy , optical correction , lateral recti hypofunction , alphabetical variations ( v or a variations ) , absence of bilateral symmetric upshoot , dvd , nystagmus , anomalous head positions , amblyopia , and cross fixation were not associated with the need of reoperation .
we found that demographic factors , such as sex and family strabismus history , are associated with a higher risk of reoperation . on the other hand , some clinical features , including a few factors classically associated with worst motor outcome , such as preoperative angle , dvd , and amblyopia , did not influence , in our cohort , the incidence of reoperation .
patients with hypertropia in preoperative examinations have a significantly decreased reoperation rate . concerning the timing of surgery , the first operation after 36 months of life
is associated with a higher frequency of reoperation than children operated before 24 months of life ; on the basis of the earlier considerations concerning binocular vision and reoperation rate , we suggest performing ie surgery between 12 and 24 months to achieve an optimal motor alignment .
the aim of this study was to identify clinical and demographic factors associated with misalignment after first surgery performed on children affected by infantile esotropia to evaluate the reoperation rate . 
 a retrospective study was carried out , analyzing data from 525 children who underwent bilateral medial recti recession , bilateral lateral recti resection , and inferior oblique recession and anteroposition by the same surgeon ( am ) . 
 postoperative evaluation included assessment of motor alignment at approximately 3 months , 6 months , 1 year , and 5 years . 
 statistical analysis was performed with a logistical regression model in which the dependent variable was the presence / absence of reoperation . 
 we found that late surgery ( after 3 years of age ) and a family history of strabismus are associated with a higher risk of reoperation , while some clinical factors , including some classically associated with worst motor outcome as preoperative angle , dissociated vertical deviation , and amblyopia , did not influence the incidence of reoperation in infantile esotropia . 
 male patients and patients with hyperopia in preoperative examinations have a significantly decreased reoperation rate .