REVIEW OF “A RANDOMIZED TRIAL EVALUATING EFFICACY OF OVERMINUS LENSES COMBINED WITH PRISM IN THE CHILDREN WITH INTERMITTENT EXOTROPIA”
Citation: Feng Y, Jiang J, Bai X, Li H, Li N. A randomized trial evaluating efficacy of overminus lenses combined with prism in the children with intermittent exotropia. BMC Ophthalmol. 2021 Feb 6;21(1):73. doi: 10.1186/s12886-021-01839-0. PMID: 33549081; PMCID: PMC7866701.
The authors have conducted a randomized clinical trial to evaluate the efficacy of overminus lenses combined with prism spectacles in 60 children aged 3–6 years with intermittent exotropia (IXT). The authors conclude that a significant improvement in the control of IXT and stereopsis was achieved with overminus spectacles with prism. The improvement was achieved by reducing the angle of strabismus in children with IXT. The authors state that the treatment, as they have done, does not cause myopia and recommend further randomized control trials (RCTs) to assess the effect of overminus spectacles with prism after the treatment has been discontinued.
IXT is a form of strabismus that is common in young children. Surgery is considered effective to correct the IXT and restore binocular vision. The timing of surgery in IXT is controversial and variable success rates after surgery are reported. Overminus glasses are a non-surgical option that is useful to treat this condition. But the chances of inducing myopia and recurrence of squint on withdrawing the glasses are concerns with this treatment.[2,3] The base in relieving prisms helps in reducing the angle of deviation and the need for fusional convergence, and thus improves the sensory fusion. In this study, the author wants to find out the efficacy of overminus with prisms in the treatment of IXT in children aged 3–6 years with IXT.
The authors used a randomized clinical trial design as this is an interventional study. The clinical trial protocol was registered with the Chinese Clinical Trial Registry. The authors have not specified if the design is a superiority, equivalence, or non-inferiority trial. However, the authors have used a one-sided hypothesis test to estimate the sample size indicating that they are looking specifically for benefits in one direction or superiority of the intervention. The sample size was estimated at 55, and a 10% loss to follow-up was assumed. Study subjects were randomly assigned using a permuted block design stratified by exotropia control (0–3, 4–6, 7–9) with equal probability to the treatment group or observation.
The authors have included hypermetropic children with IXT. However, they have not recorded the best-corrected visual acuity with overminus glasses. They had excluded those with neurological disorders, oblique overaction, dissociated vertical deviation, anisometropia, and inadequate follow-up. The distance stereo acuity is the first parameter that is lost in intermittent divergent squint (IDS); however, this statistical parameter has not been considered by the author. The asthenopic symptoms which can happen with these types of glasses are also not mentioned. The examination is done by a masked examiner in all cases. They have not mentioned any cases of amblyopia or whether patching has been given at any point in time to these patients.
The control and intervention groups were comparable at baseline for the parameters studied. The outcomes measured were exotropia control, the deviation for distance and near, the refractive error, and near stereo acuity. The author compared the mean of these parameters at 1, 3, 6, and 12 months. At the end of 12 months, 71.4% of children in the intervention group had good control with an NCS score of less than 3, compared to 65.5% with an NCS score of 4–6 and 27.6% with more than a score of 7 in the observation group. The exotropia control, the deviation at a distance and near, and the near stereo acuity were found to be statistically significant compared to the observer group. The author did not find any myopic shift in the intervention arm, perhaps due to the sole inclusion of hypermetropic children.
The strengths of the study include the RCT design which confers statistical robustness to the study. A formal sample size estimation was done prior to the study and both the groups were comparable with respect to baseline characteristics.
The limitations include a short follow-up time and exclusion of premyopes and myopic children. They have not reported the axial length. There is no mention regarding the compliance of children with these glasses. They have not analyzed the control of exotropia on weaning from these glasses.
The result from this study is useful to design future studies with longer follow-ups. The results can be taken into clinical practice in preschool children with IXT and to preserve the binocular vision till the child is deemed fit for surgery, but the authors have chosen only a certain subgroup of refractive errors for study and hence generalization of the results to all refractive errors is not possible. Overminus glasses with prisms must be studied for all types of refractive errors.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
1. Govindan M, Mohney BG, Diehl NN, Burke JP, Incidence and types of childhood exotropia:A population-based study. Ophthalmology 2005;140:546–7.
2. Chen AM, Ayse Erzurum S, Chandler DL, Hercinovic A, Michele Melia B, Bhatt AR, et al., Overminus lens therapy for children 3 to 10 years of age with intermittent exotropia:A randomized clinical trial. JAMA Ophthalmol 2021;139:464–76.
3. Mangad S, Mohan L, Vijayalakshmi M, Krishnan P, Babu S, Role of overminus therapy in intermittent exotropia. Kerala J Ophthalmol 2018 3038–42.