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Dr.Kruti Shah,Dr.Vijayalakshmi P

Introduction:

Consecutive strabismus or overcorrection is a rare but important complication of strabismus surgery. It can be spontaneous also in some patients without undergoing surgery.

The incidence of consecutive exotropia has been reported ranging from4%-27% [1-5]& consecutive esotropiaaround 2.6%-25% [6-10]. The purpose of this study was to identify the risk factors causing consecutive strabismus.

Material & methods:

It was a retrospective observational study, done by reviewing the clinical records of the patients operated at our hospital in the time interval between the year2003-2015, and who had a regular follow up for atleast 2 years or more.

Consecutive exotropia (XT) was defined as an exodeviation of 10 PD or more measured at near or at distance 4 weeks or more postoperatively.

Consecutive esotropia (ET) was defined as an esodeviation of 10 PDor more measured either at near or at distance 4 weeks or more postoperatively.

Exclusion criteria: The exclusion criteria included any pre-existing ocular condition, follow up <2 years, sensory strabismus, restrictive and paralytic strabismus.

All patients underwent ophthalmologic examinations including visual acuity exams, cycloplegic refraction (using atropine 1% in children between 1-5 years of age, Cyclopentolate 1% &Tropicamide-Phenylephrine HCl combination over 5 years of age),dilated fundus examination, ocular deviation measurements, and eye movement exams. Preoperative deviations were measured using alternate prism cover tests while the subject was fixing at a 20/30 target at 6m and 33cm.

Krimsky’scorneal reflex method was performed, only in the ones with neurological disorder or uncooperative with an alternate prism cover test.

Before disruption of fusion by alternative cover test, a Worth four-dot test was performed at near (33 cm) and far (6 m) test distances.Stereopsis was measured using TNO charts for near for patients more than 4 years.

Amblyopia was defined as a difference of two lines or more using Snellen’s chart best-corrected visual acuity (BCVA) or lack of central, steady, and maintained fixation in infants. Amblyopia was treated with patching according to ATS guidelines afterrefraction correction and in patients younger than 12 years old, until there was no further improvement for at least 6 months.

Surgical discussion – All the surgeries were performed under general anaesthesia&operating microscope. In the cases with free alternating fixation and good bilateral visual acuity,aB/LLR recession in case of  intermittent or alternating XT&B/L MR recession was done in case of infantile ET.U/Lrecession / resection surgery was done in presence of amblyopia and no alteration.B/L resection of medial rectus or lateral rectus for exotropia or esotropia respectively was not done.>5.5mm of MR resection or recession was not done&>9mm LR recession or resection was not done.

IOOA was graded on a scale of 0 (no overaction) to +4 (severe increase in adduction) If there was IO overaction of +2 or more, IO weakening procedure was done. No surgery for DVD was done.

The patients were followed up postoperatively on day 1, 1st month, 3rd month and 6th month, and 1 year &then 6 monthly thereafter.

Various risk factors were assessed and divided as General,preoperative, intraoperative, postoperative risk factors. The General factors included preterm/term, h/o low birth weight,family h/o strabismus, h/o consanguineous marriage in parents, neurological syndromes, presence of PVL.

Preoperative risk factors included – age of onset of strabismus, age at which the primary surgery was done, BSV, presence of refractive error, amblyopia, IO overaction, DVD, presence of A-V patterns, time interval between 1st presentation and date of surgery.

Intra operative – U/Lvs.B/L, oblique muscles operated at the time of primary Surgery.

Postoperative: BSV, collapse of A-V pattern, IO or SO overaction,DVD.

Results:The consecutive (consecutive) strabismus patients who had a regular follow up and complete medical records were included in the study. There were total 32 consecutive strabismus patients out of which 24(75%) developed consecutive XT and 8(25%) developed consecutive ET.Total 13(40.62%) patients were female, out of which 7(29.16%) had consecutive XT and 6 (75%) had consecutive ET.

The risk factors like preterm, LBW, seizures, consanguineous marriage, neurological disorders and family history were found infrequent (Table1). In our study, 6 patients had birth weight less than 2500gms, none of them were very low birth weight babies <1500gms. Total 6 patients with consecutive XT had neurological disorders: 3 had PVL, 2 had CVI and 1 had epilepsy.

Table1:Incidence of General factors

  Total Consecutive  exotropia Consecutive esotrropia Remarks
Preterm 5(15.62%) 4(16.66%) 1(14.28%)  
LBW 6(18.75%) 6(25%) 0 5 babies BW not known
Neurological disorder 6(18.75%) 6(25%) 0 3 PVLs, 2 mild CVI- delayed milestones, 1 epilepsy
Consanguineous marriage 3(0.09%) – 3(0.09%) 3 status not known
Family history 4(12.5%) 2(8.3%) 2(25%)  

 Table 2 shows1stpresentation of the patients at our hospital for strabismus, which was at an average age of 2.71yrs ranging from 5 months to 12yrs. There was earlier presentation of consecutive ET patients at the avg. age of 1.7yrs as compared to consecutive XT patients, around 2.8yrs. Majority of the patients reported at earlier age.

The time interval between the 1stprimary surgery and development of consecutive strabismus was also investigated. In our study, we found a higher exotropic shift acrosstime in the consecutive XT group. 10 (41.66%) developed consecutive XT between 1-5 years postoperatively. However,7(29.16%) patients developed consecutiveXT 5 years postoperatively with 1 patient developing after 13 years of initial surgery. In other group, patients developed consecutive ET at mean time interval of 1.9yrs,(range 1 month- 3.5 years).

Table 2:time interval between primary surgery and development of consecutive strabismus

Time interval between primary surgery and development of consecutive strabismus   Total Consecutive XT Consecutive ET Remarks
Average total 3.17yrs

(1month- 13yrs)

 3.8yrs(1 month- 13years) 1.9yrs (1 month-3.5 years Records not available for 1 pt in each group
In terms of patients on the post-operative follow ups.
At 1 month 7(21.87%) 5(20.83%) 2(25%)  
>1 month-<1 year 3(9.3%) 1(4.17%) 2(25%)  
1 yr- 5yrs 13(40.62%) 10(41.66%) 3(37.5%)  
>5yrs 7(21.87%) 7(29.16%) –  

 

We investigated the age of the patient at the time of surgery and the interval between the onset of the deviation and the surgical intervention. The more recent patients, tended to undergo surgery at an earlier age or closer to the onset of their deviation. 15/32(46.87%) patients who developed consecutive strabismus were <3 years of age. No surgery was done below 1 year of age. Table 3 shows distribution of patients undergoing surgery with respect to age, maximum patients (46.87%) were operated at < 2years of age, with the number decreasing with increasing age.

Table 3: Correlation between age at surgery & the development ofconsecutive strabismus

Age at surgery Total Consecutive XT Consecutive ET
1-2 15(46.87%) 13(54.16%) 2(25%)
3-4 8(25%) 5(20.83%) 3(37.5%)
5-6 4(12.5%) 2(8.3%) 2(25%)
7-8 2(6.25%) 1(4.16%) 1(12.5%)
9-10 1(3.12%) 1(4.16%) –
11 & above 2(6.25%) 2(8.3%) –

Amblyopia has commonly been identified as one of the important risk factors in the development of consecutive strabismus and was found only in 9(28.5%) patients in our case series, (table 4), with 8 (33.33%) patients in consecutive XT and 1(12.5%) in consecutive ET group.

A high degree of hyperopia/high myopia has been thought to be responsible or an important factor in producing a consecutive strabismus. Our study did not show this to be true (Table 4). 11(34.37%) patients had a refractive error with a spherical equivalent between        -1.50D to +2 D.  A high degree of anisometropia, which had been expected, was also not found..

Table 4:Presence of Amblyopia and refractive error(spherical equivalent)

    Total consecutive Consecutive XT Consecutive ET Remarks
Amblyopia present   9(28.5%) 8(33.33%) 1(12.5%) Record was not available for 1
Refractive error (spherical equivalent) Patients with ref. error 15(46.87%) 11(45.83%) 4(50%)  
-1.50D to +2D 11(34.37%) 7(29.16%) 4(50%)  
Hyperopia>+2D – – –  
Myopia >-1.5 D 6(18.75%) 5(20.83%) 1(12.5%)  
Anisometropia>1.25D 2(6.25%) 2(8.3%)    
  High myopia – – –  

Both the types of surgeries unilateral recess/resect andB/Lrecessions developed consecutive strabismus.U/Lrecession resection was performed in 15(62.5%) cases in consecutive XT and B/L MR recession in 9(37.50%) cases. In consecutive ET 50% patients underwent B/L LR recessions and 50% patients underwent U/L recession- resection procedure. Pre-operative assessment of fusion and stereopsis could not be assessed in 13 patients of the whole cohort may be due to small age, but was tried in all. However 8 patients had fusion with 1 had stereopsis in consecutive XT group. 2 patients in consecutive ET group had fusion and stereopsis, postoperatively. 

Table 5: Types of surgery performed

Type of surgery Total consecutive Consecutive XT Consecutive ET Remarks
U/L recession &resection 19(59.37%) 15(62.5%) 4(50%)  
B/L MR recession 9(28.12%) 9(37.50%)    
B/L LR recession 4(12.5%)   4(50%)  
Pre-operative avg. measurements n-42.11D, d-32.5D n-44.47 , d-33.75 n-35.71D, d-35D  
BSV preop 3 present , 16 absent 13 absent, 11 could not be assessed 3 present, 3 absent, 2 could not be assessed Could not be assessed in 13 patients
BSV when 1st consecutive strabismus noted 10(31.25%) present, 22 absent 8(33.34%) present , 1 had stereopsis 2(25%) present, 2 also had stereopsis  

Inferior oblique overaction has also been reported as a risk factor for consecutive strabismus. In our case series, inferior oblique overaction was found in 19 (59.3%) patients. Patients who had IO OA > +1 grade underwent IO weakening procedureof gradedrecession and anterior positioning at the time of primary surgery for horizontal muscles.

Table 6 shows 14(43.75%) patients underwent IO muscle surgery with 2 patients underwent bilateral  IO weakening. 7 patients had residual IO overaction of +1 to +2. 7 (21.8%) patients were found to have IO OA after primary surgery, as it was not detected preoperatively.

DVD was found in 6 (18.75%) preoperatively. None of the patients underwent surgery for DVD. However, after the surgery total 20 (62.5%) patients were found to have DVD, 17(70.8%) patients in consecutive XT group and 3(37.5%)patients in consecutive ET group.

Table 6:Incidence of IOOA, IO OA Sx& DVD

    Total

 

 Consecutive XT Consecutive ET
IO OA preoperative   19 (59.3%)IO OA, 15-B/L IO OA & 4- U/L IO OA 15(62.5%) IO OA, 12 –B/L IO OA & 3- U/L IO OA 4(50%) IO OA, 3- B/L IO OA & 1 U/L- IO OA
IO Sx done

 

   14 IO Sx, 12- B/L IO Sx& 2-U/L IO Sx 11 IO Sx, 10 -B/L IO Sx& 1-U/L IO Sx 3 IO Sx, 2- B/L IO Sx& 1 -U/L IO Sx
Residual IO OA   7 IO OA , 3 B/L IO OA, 4 U/L IO OA 6 IO OA, 3 -B/L IO OA , 3 -U/L IO OA 1 U/L IO OA
IO OA noted post primary Sx   7 IO OA, 5 -B/L  IO OA, 2 – U/L IO OA 6 IO OA, 5 – B/L IO OA , 1 U/L IO OA 1 U/L IO OA
DVD Noted prior to primary Sx 6 present, 4-B/L , 2-U/L 4 present – 3-B/L& 1-U/L 2 present-1-B/L& 1 U/L
Total Noted after primary Sx 20(62.5%) present, 6- B/L , 14 U/L 17(70.8%)present, 3-B/L , 14- U/L 3(37.5%) present ( 3 B/L)
DVD Sx done – – – –

Discussions:

In this study we followed up the patients with consecutive strabismus who had a regular follow up forat least 2 years asthe success or failure of a surgical approach cannot be evaluated within a short follow-up period. The consecutive strabismus may not develop until years after the surgery.

As per general factors concerned, the prevalence of strabismus & amblyopia is substantially higher in low birth weight, premature infants [11, 12] or those who suffer from perinatal hypoxia [12, 13]. Charles and Moore [14] compared the outcomes of strabismus surgery for infantile esotropia with /without neurological problems and /or prematurity. They found similar frequency of orthophoria in both groups and they recommend not delaying the surgery for infants with neurological problems. Bang and Brodsky [15] reported that large angle exodeviations might be corrected by adjusted surgical numbers in patients with neurological impairment. Sekeroglu THet al.[16] found neurological factors like cerebral palsy, epilepsy and mental retardation (undetermined origin) as significant risk factors for development of consecutive XT, with 6 out of 14 patients with consecutive XT. In our study, though not very frequent, total 6 patients with consecutive XT had neurological disorders, 3 had PVL, 2 had CVI and 1 had epilepsy.

Ganesh et al. [5]& Folk et al. [17] found that age at onset, age at surgery and the amount of surgery were not related significantly to the risk of consecutive XT. Richard &Parks [7] and Dunlop [18] found that age at the time of surgery was independent of the development of consecutive ET, as was demonstrated in this study. However, in our study the age distribution was not equal, and more number of patients will be needed to comment.

It is reported that the incidence of amblyopia wasabout20.3–66 % in consecutive XT patients with highest in Yurdakulet al. study of 66% [5, 17, 19, 21, 22]. Ceylanet al.[23]and Ganesh et al.[5] reported higher rates of amblyopia in the consecutive XT groups, but these results were not statistically significant.Jang et al. showed higher rates of amblyopia in consecutive ET patients. However, it was not a frequent finding in our case series, in either of the groups.

While Keech and Stewart [24] concluded that the incidenceof consecutive ET was not related to the type of surgery and so did Kim HSet al. [9], the incidence was found higher in theLROU-rec group than in the R&R group in the study by Park et al. [25]. There was no difference in the present study in consecutive ET group.

Yurdakul [22]and Folk et al. [17] found higher rates of consecutive XT with U/L recess+ resect surgery as compared to B/LMR recession. In the present study, 15(62.5%) patientswho underwent U/L surgery developed consecutive XT as compared to 9(37.5%) in B/L MR recess group.

 Folk et al.[17] reported that limitation of adduction was observed at higher rates in consecutive XT patients and was greater in the patients with multiple surgeries. Oguzet al.[26]and Ganesh et al.[5] also reported limitation of adduction as a risk factor for developing consecutive XT. In our study, there were no postoperative adduction limitation found; therefore, we could not evaluate this as a risk factor.

According to Fletcher and Silvermann [27], the vertical deviation and pattern strabismus were responsible risk factors for development of consecutive XT and consecutive ET. Ceylanet al. [23] found that DVD was not significantly different between the consecutive XT groupand the non-exotropic group. Han SYet al. [28]reported DVD as a significant risk factor for development of consecutive XT as it triggers the development of XT due to loss of macular and peripheral fusion and imperfect binocularity.

Ceylanet al.[23] reported higher incidence of IOOA of 26.7 % in the consecutive XT, compared to 7.4 % in the non-exotropic group. IOOA was found to be higher in the consecutive XT group, but was not statistically significant,in the study by Han et al.[28]. With regard to vertical deviation, none of the existence or non-existence of inferior oblique overaction, dissociated vertical deviation, and comitant vertical deviation influenced the onset of consecutive ET in Jang JH et al. study[29].

In the present study, IOOA and DVD were found as most common factors for development for consecutive XT and consecutive ET. Table 7 and table 8 shows various significant or frequent factors investigated by various studies

Table 7: Consecutive XT: mainrisk factors reported by various studies

Risk Factors Our studysummary of consecutiveXT group Yurdakulet al. (JPOS 2014)  Ganesh etal. (Actaophthal 2011) Folk et al. (BJO 1983) Han et al. (Jpn J ophthalmol 2016 Ceylanet al.(Euro ophthal 2014)
Amblyopia   66%   37.6% 50%  
BSV   10.6%        
IO OA 87.5% 27.7%       26.7%
DVD 70.83%       29.1%  
Adduction deficit – 29.8% significant     30%
Asymmetrical SX   61.7%        
Age at primary Sx(mean)            
Multiple surgeries –   significant 13.2%    

Table 8:Consecutive ET: main risk factors reported by various studies.

Risk Factors Our study summary. Kim HSet al. (KJO 2007) Jang et al. (Grafesophthalmol 2012
High myopia     High myopia (50%)
Amblyopia 12.5%   22.7%
IO OA 62.5%    
DVD 37.5%    
Lateral incomitance Not assessed. 23.8%  

Conclusion:We found the presence of DVD, IOOA as most common factors responsible for consecutive strabismus. Unilateral R&R surgery was also found as a frequentfactor in consecutive exotropia group.

The current study is a retrospective study with a limited number of patients. So follow up of larger no. of patients would be required. Consecutive strabismus may not appear until many years after surgery, so long term follow up should be done in these patients.

However, the long duration postoperatively before the onset of consecutive strabismus  suggest[30] that control is possible, and everything should be done to maintain this. Prisms, refractive error correction, orthoptic exercises, patching therapycan be tried before taking up the consecutive strabismus patients for surgery. 

(Abbreviations: XT- exotropia,ET- esotropia, Yrs- years, PD- prism dioptres, Sx- surgery, IO OA- inferior oblique overaction, Avg- average) 

Referrences

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