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 Table of Contents  
Year : 2018  |  Volume : 30  |  Issue : 1  |  Page : 38-42

Role of overminus therapy in intermittent exotropia

1 Department of Squint and Pediatric Ophthalmology, Comtrust Eye Hospital, Kozhikode, Kerala, India
2 Department of Ophthalmology, MES Perinthalmanna, Malappuram, Kerala, India

Date of Web Publication7-Jun-2018

Correspondence Address:
Sharika Erikapatil Mangad
“Padmasudha,” Thrikanapathiyaram, P.O Chittanda, Via Wadakanchery, Thrissur - 680 585, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/kjo.kjo_7_18

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Aim: The aim is to study the change in Newcastle Control Score (NCS) and angle of deviation after a trial of overminus therapy in intermittent exotropia (IXT).
Context: Overminus therapy in IXT.
Settings and Designs: This prospective observational study was conducted at Comtrust Eye Hospital, Calicut, Kerala, which is a tertiary eye care center from July 2015 to May 2017.
Materials and Methods: Fifty-three children with IXT, aged 1–5 years, were recruited. NCS scores and angle of deviation were recorded. Treatment was instigated with the minimum minus lens required to achieve control of the manifest deviation. NCS and angle of deviation were recorded with the overminus glasses at 6 weeks, 6 months, and 1 year.
Statistical Analysis: Data were tabulated and analyzed using the SPSS software (SPSS statistics for Windows 17.0 Chicago, SPSS Inc). Paired t-test was used to compare change in NCS and angle of deviation before and after treatment. P < 0.05 was taken as statistically significant.
Results: Fifty-three children were recruited, 31 females and 22 males with a mean age of 3.6 ± 1.633 years. Majority were of the basic type of IXT. The NCS at 1 year showed significant reduction from baseline values. At 1 year, 27% patients had the same NCS as baseline, 32% showed a reduction by 1, 21% reduced by 2, and 5% showed a reduction by 3 in the total score. The angle of deviation with the overminus for both distance and near also showed significant reduction.
Conclusion: This study showed definite improvement in control of IXT with overminus, and hence, a trial of overminus therapy is recommended for IXT in children below 5 years, as surgery has its own side effects like overcorrection, leading to consecutive esotropia with loss of stereopsis and high amount of recurrence.

Keywords: Intermittent exotropia, Newcastle Control Score, overminus

How to cite this article:
Mangad SE, Mohan L, Vijayalakshmi M S, Krishnan P, Babu SP. Role of overminus therapy in intermittent exotropia. Kerala J Ophthalmol 2018;30:38-42

How to cite this URL:
Mangad SE, Mohan L, Vijayalakshmi M S, Krishnan P, Babu SP. Role of overminus therapy in intermittent exotropia. Kerala J Ophthalmol [serial online] 2018 [cited 2018 Jun 23];30:38-42. Available from: http://www.kjophthal.com/text.asp?2018/30/1/38/233785

  Introduction Top

Intermittent exotropia (IXT) is the most common form of childhood-onset exotropia with a reported incidence of 32/100,000 children below the age of 19 years.[1] In IXT, binocular fusion occurs most of the time and squinting occurs only when this fusion is disrupted.

Treatment goals in IXT are mainly to attain motor alignment and binocularity. Surgical and non- surgical methods are tried to accomplish these goals, but the best treatment options are still debatable.

Some authors advocate early surgery,[2] to prevent conversion into constant exotropia, and they postulated that the patients who undergo surgery before 7 years of age or <5 years of onset of squint achieve better binocularity. Whereas, others [3] opine that surgery should be delayed till the child gets older; as these patients have good fusional reserves and can control their deviation. Hence, there is a better chance of binocularity if operated later. Furthermore, all cases of IXT are not progressive.

A study was conducted [4] to compare the outcome of surgical versus nonsurgical methods in IXT showed that the difference in the cure rate between the two groups was not statistically significant. The nonsurgical group had no adverse effects like overcorrection, leading to consecutive esotropia or recurrent exotropia and had the additional advantage that all the patients had bifixation status at the end of 5 years. As surgery has its own side effects, it is worth giving a trial of nonsurgical management in IXT to promote binocular viewing and binocular control of their deviation.

The role of these nonsurgical methods like overminus therapy has not been conclusively validated by previous studies, and further studies are needed to determine their role and efficacy in the management of IXT. The basic principle in prescribing overminus glasses is that the child wearing the overminus correction accommodates more to see near objects more clearly, there is more of accommodative convergence which helps to control the divergent deviation.

This study was undertaken to study the effectiveness of overminus therapy in IXT.

  Materials and Methods Top

This study was conducted in 53 children aged 1–5 years with IXT having Newcastle Control Score (NCS) <6 and minimal angle of deviation more than 10 PD for both distance and near. Children who were previously treated (with surgery or spectacles) for IXT, those with vertical deviations, cataract, and retinal pathology were excluded from the study. Informed consent was taken from the parents.

A detailed history regarding the age of onset, the frequency of squinting noticed by the parent at home in terms of percentage of waking hours was elicited and the parental NCS score was recorded as either - 0.1 or 2 [Table 1].
Table 1: Newcastle control score

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The visual acuity was recorded in each eye. The tests used for assessing the visual acuity depended on the age of the child. Children more than 3 years, but <5 years, were tested using the HOTV or picture charts. Children who could not be tested with either these were tested using the Teller acuity cards, but the results were variable. Even with these, visual acuity could not be tested in children, particularly of 1–2 years of age.

They were then subjected to cover tests by the ophthalmologist, and a rough estimate of distance and near deviation was made (in degrees). The child was made to fixate at a target at 6 m for distance and at 33 cm for near. The rate of recovery was also noted both for distance and near, if they fused spontaneously, or after a blink or refixation, or remained dissociated for long. The NCS office scores both for distance and near were recorded. The angle of deviation was then quantified in terms of prism diopters (PDs) both for distance and near by the optometrists using loose prisms (available as 5, 10, 15, 20, and so on).

The child was then subjected to cycloplegic refraction (either using atropine or cyclopentolate depending on the age) and fundus examination. All children under 5 years were prescribed overminus, ranging from −1.00 to −3 D over the existing refractive error correction based on wet retinoscopy measurements. The minimum minus power to keep the deviation under control was put in the trial frame and slightly increased in 0.5 D till the child could tolerate and visual acuity was not compromised. Hypermetropia if present was undercorrected. This was possible only in some children, and in others, −1.0 D was prescribed, that is, −1.0 D in addition to the existing refraction.

  Results Top

Fifty-three patients were analyzed. The mean age in this group was 3.60 ± 1.633 years. There were 31 (62.2%) females and 22 (41.5%) males.

Types of IXT – 39 were having basic type, 13 had divergence excess type, and 1 has convergence insufficiency type of IXT.

Pre-existing refractive errors – [Figure 1] – 20 children had myopic astigmatism, 5 had simple myopia, 1 had mixed astigmatism, 12 were on the hypermetropic side, and 15 children had no refractive errors.
Figure 1: Preexisting refractive errors

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NCS at presentation – only 1 each was having NCS in the extremes (NCS 1 and 6) at presentation. Twenty (37.7%) had NCS of 3, 18 (33.9%) had NCS of 4, and 13 (24.5%) had NCS of 5 at presentation. There was no one with NCS of 2 at the initial visit.

Newcastle Control Score mean scores at 6 weeks

There was a significant change in the NCS scores at 6 weeks with the overminus glasses.

The mean NCS home score changed from 1.37 ± 0.486 to 1.11 ± 0.312 (P < 0.001). NCS office distance (NCS D) scores changed from 1.4 ± 0.524 to 1.17 ± 0.517 (P < 0.001) and NCS office near (NCS N) values changed from 1.18 ± 0.429 to 1.05 ± 0.482 (P = 0.002). The NCS total score changed from 3.95 ± 0.926 to 3.31 ± 1.045 (P < 0.001). All of these values were statistically significant.

At 6 months, mean NCS home scores reduced to 1.07 ± 0.315, with P < 0.001. The mean NCS office distance scores reduced to 1.12 ± 0.441 from the initial value of 1.38 (P < 0.001). The NCS office near values showed a reduction from 1.18 to 1.03, which was statistically significant (P < 0.05). Mean NCS total scores reduced from 3.94 ± 0.912 at initial presentation to 3.24 ± 0.979 at 6 months after overminus glasses (P < 0.001).

At 1-year follow-up [Figure 2] the mean NCS home scores reduced from the initial value of 1.36 ± 0.483 to 0.97 ± 0.183, the mean NCS office distance reduced from 1.32 ± 0.507 to 1.05 ± 0.471 and NCS near scores reduced from 1.15 ± 0.407 to 0.93 ± 0.410, all of which had P value (P < 0.05). Mean NCS total scores reduced from 3.83 ± 0.894 to 2.95 ± 0.797 (P < 0.001).
Figure 2: Reduction in mean Newcastle Control Score total over 1 year

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Reduction in Newcastle Control Score total numerical values at 1 year

The total NCS numerical values were also compared with the baseline values to see how much each value (at the end of 1 year) reduced or increased as compared to baseline values [Figure 3].
Figure 3: Reduction in total Newcastle Control Score at 1 year

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  • Ninety patients (35.8%) showed a reduction of NCS score by 1 from the initial values
  • Thirteen patients (24.5%) showed a reduction by 2
  • Three patients (5.6%) showed a reduction of total NCS score by 3 and
  • Seventeen patients (32%) showed the same NCS values as that at presentation.

Only one patient showed deterioration and was advised surgery (increase in NCS scores from baseline).

Changes in angle of deviation with the overminus glasses [Figure 4]
Figure 4: Change in angle of deviation (distance and near) over 1 year

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At 6 weeks, in children given overminus correction, the mean angle of deviation values for distance had reduced from 31.17 ± 9.910 to 21.64 ± 9.044, with the overminus glasses, which was statistically significant (P < 0.001). The angle of deviation for near also reduced from 27.38 ± 10.018 to 19.84 ± 6.956 which also was statistically significant (P < 0.001).

Change in angle of deviation at 1 year

At 1 year, the values for angle of deviation at distance and near with glasses showed statistically significant reduction (P < 0.001), and for distance, the angle of deviation reduced from 29.22 ± 9.588 to 27.76 ± 9.185 which was statistically significant (P = 0.026) [Figure 4].

  Discussion Top

Surgical outcomes in IXT are variable. Although they achieve good motor alignment,[5] it has a negative effect on stereoacuity due to consecutive esotropia [4] and high number of recurrences requiring a second surgery.

The basic principle in prescribing overminus glasses is that the child wearing the overminus correction accommodates more to see near objects more clearly, there is more of accommodative convergence which helps to control the divergent deviation.[6]

Age distribution

This group had mean age of 3.60 ± 1.633 (below 5 years). This was mainly to avoid asthenopia in school-going children due to the excess accommodation they exert to see near objects clearly (while wearing the overminus). Kushner in his study had prescribed overminus to all children under 7 years if they did not complain of asthenopic symptoms.[7]

Watts et al.[8] evaluated the efficacy of overminus therapy in children in the age group of 2–17 years. In another study by Rowe et al.[9] studying the effect of overminus therapy, there was no age restriction for recruitment.[9]

In our study, only nine patients discontinued the therapy due to intolerance, the remaining children did not complain of any symptoms. In previous studies mentioned, it was not stated if the patients complained of asthenopic symptoms.

Visual acuity

The visual acuity was recorded if possible at 6 weeks, 6 months, and 1 year. Only the minimal overminus to keep the deviation under control and not to compromise visual acuity was prescribed. There were no significant visual acuity changes noticed, as most patients retained the initial vision even with the overminus glasses. That the overminus was not associated with induced myopia was found in previous studies.[7]

Change in Newcastle Control Score scores

The NCS showed significant reduction with the child wearing the overminus at all follow-up visits. Both the parental and office scores had shown statistically significant reduction from baseline values. At 1-year follow-up, 27% patients had the same NCS as baseline, 32% showed a reduction by 1, 21% reduced by 2, and 5% showed a reduction by 3 in the total score. About 2% showed deterioration (increase in total score). About 66% patients showed some improvement from baseline scores.

This had some similarity to findings in the study by Rowe et al.[9] of 21 patients with IXT treated with overminus lenses. They found 100% improvement in the short term (within 6 months of commencing the therapy). Medium-term follow-up (6–24 months after reducing the overminus) also showed good improvement in NCS. It reduced from median NCS of 4, at presentation to a mean value of 1 (reduction by 3) at 24 months. Long-term follow-up (6–39 months after cessation of treatment) showed statistically significant reduction of distance and near deviation over time (P = 0.004 and P < 0.0011, respectively). However, this study had only 21 patients compared to 53 patients in our study. Moreover, the effects postcessation of treatment could not be studied.

In the study by Watts et al. 24 children with IXT (2-17 years) were prescribed overminus therapy and it was found that there was statistically significant improvement in the control of IXT (P = 0.041) using NCS. In the group with NCS ≤4 before treatment (n = 16), 75% had improved scores posttreatment compared with 62.5% in the other group (n = 8), which had pretreatment NCS more than or equal to 5. This study also had a small sample size. The division into two groups based on initial NCS was not done in our study.

In our study, also, about 66% showed some improvement in NCS scores from baseline.

Changes in angle of deviation

The deviation measured in PD was found to be statistically significant when measured with the glasses. At 6 months, the angle of deviation values at distance showed reduction from 31.00 ± 9.929 to 21.00 ± 8.848 which showed a statistically significant reduction (P < 0.001), with overminus glasses. The values for angle of deviation at near changed from 27.11 ± 9.819 to 20.00 ± 7.448 which showed statistically significant reduction (P < 0.001). In the study by Watts et al.,[8] they prescribed overminus therapy in IXT. The mean pretreatment distance angle was 28.5 ± 10 PD, and the mean posttreatment distance angle was 18.3 ± 8.9 PD (P = 0.001), which was a similar reduction shown in our study also.

  Conclusion Top

There was a definite female preponderance in IXT. The predominant refractive error in IXT was myopic astigmatism, followed by simple myopia. The majority of patients had basic type of IXT. There was no significant correlation between control as assessed by NCS and angle of deviation. NCS scores 5–6 will not improve with nonsurgical methods and will need surgery. Overminus therapy definitely improved the control and deviation of IXT.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Mohney BG. Common forms of childhood strabismus in an incidence cohort. Am J Ophthalmol 2007;144:465-7.  Back to cited text no. 1
Abroms AD, Mohney BG, Rush DP, Parks MM, Tong PY. Timely surgery in intermittent and constant exotropia for superior sensory outcome. Am J Ophthalmol 2001;131:111-6.  Back to cited text no. 2
Yang CQ, Shen Y, Gu YS, Han W. Clinical investigation of surgery for intermittent exotropia. J Zhejiang Univ Sci B 2008;9:470-3.  Back to cited text no. 3
Hatt SR, Leske DA, Liebermann L, Holmes JM. Quantifying variability in the measurement of control in intermittent exotropia. J AAPOS 2015;19:33-7.  Back to cited text no. 4
Buck D, Powell CJ, Sloper JJ, Taylor R, Tiffin P, Clarke MP, et al. Surgical intervention in childhood intermittent exotropia: Current practice and clinical outcomes from an observational cohort study. Br J Ophthalmol 2012;96:1291-5.  Back to cited text no. 5
Richardson S, Gnanaraj L. Interventions for intermittent distance exotropia. The Cochrane database of systematic reviews. 2003:CD003737.  Back to cited text no. 6
Kushner BJ. Does overcorrecting minus lens therapy for intermittent exotropia cause myopia? Arch Ophthalmol 1999;117:638-42.  Back to cited text no. 7
Watts P, Tippings E, Al-Madfai H. Intermittent exotropia, overcorrecting minus lenses, and the newcastle scoring system. J AAPOS 2005;9:460-4.  Back to cited text no. 8
Rowe FJ, Noonan CP, Freeman G, DeBell J. Intervention for intermittent distance exotropia with overcorrecting minus lenses. Eye (Lond) 2009;23:320-5.  Back to cited text no. 9


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]


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