One of the earliest suggestions about the use of minus lens over-correction to improve alignment in intermittent exotropia (IXT) was made by John R. Kennedy, O.D., who published an article on the subject in the American Academy of Optometry journal in 1954. But the paper that popularized the technique, particularly among pediatric ophthalmologists and classical optometrists, was authored by Caltrider and Jampolsky in the journal Ophthalmology in 1983. For those who may not be familiar with the name, Arthur Jampolsky received his O.D. degree from Berkeley and then went to Stanford for his M.D. degree, ultimately specializing in strabismus surgery.
Jamplosky suggested that it was a viable treatment option to over-minus young patients with IXT by two to four diopters, taking advantage of their AC/A ratio, while acknowledging in his original paper that a high AC/A might convert the patient into esotropia. This occurred in 2 of the 35 children that he followed for 18 months, which is not a trivial percentage. It also speaks to the probability that many children on that continuum of back-door alignment through over-accommodation might be experiencing visual stress. Numerous authors have published on the subject, and some (such as Kushner) have suggested using lesser amounts of overminus power and incorporating a moderate amount of base-in prism in the spectacles or a bifocal, presumably to mitigate the visual stress induced by the overminusing procedure.
All of the proponents of over-minus lens therapy for IXT have written re-assuringly that the technique doesn’t present a risk for triggering progressive myopia. That claim frankly never sat well with behavioral optometrists, for whom excessive minus is anathema to lens prescribing under any circumstances. Despite this, as well as the lack of any controlled research or RCTs on the subject, use of the technique persisted clinically in many circles. With a newly published randomized clinical trial from the widely regarded PEDIG group, the advisability of over-minus lens therapy in IXT has been seriously called into question.
As reported by the authors, this is the first large-scale randomized clinical trial evaluating the effectiveness and safety of overminus spectacle therapy for treatment of IXT. The trial was conducted at 56 clinical sites over a two year period between January 2017 and January 2019. Enrollment consisted of 386 children aged 3 to 10 years having IXT with poor control of alignment, and refractive status between 1 and 6 diopters of myopia. Participants were randomly assigned to either a non-overminus spectacle control group, or a treatment group with overminus by−2.50 D for 12 months, then −1.25 D for 3 months, followed by nonoverminus spectacles for 3 months.
Outcome of the study was primarily judged by mean distance IXT control scores of participants examined after 12 months of treatment, considered to be the primary outcome, and at 18 months (3 months after treatment ended) assessed by an examiner masked to treatment group. Mean distance control at 12 months was better in participants treated with overminus spectacles than with nonoverminus spectacles. However, at 18 months, there was little or no difference in mean distance control between the overminus and nonoverminus groups.
An additional goal of the study was to analyze the change in refractive status from baseline to 12 months between the groups. It was noted that the myopic shift from baseline to 12 months was greater in the overminus than the nonoverminus group, with 33 of 189 children (17%) in the overminus group versus only 2 of 169 (1%) in the nonoverminus group having a shift higher than 1.00 D. The stated conclusions of the PEDIG researchers are as follows:
“Children 3 to 10 years of age had improved distance exotropia control when assessed wearing overminus spectacles after 12 months of overminus treatment; however, this treatment was associated with increased myopic shift. The beneficial effect of overminus lens therapy on distance exotropia control was not maintained after treatment was tapered off for 3 months and children were examined 3 months later.”
While this paper may not attract as much attention as the PEDIG studies which called attention to the power of an appropriate Rx for amblyopia therapy, it should shift the paradigm in IXT treatment away from the use of overminus lenses. And, as suggested by Piano and O’Connor in the American Orthoptic Journal, other approaches need to be questioned such as patching in IXT, while the use of prism and/or pre-surgical therapy as an adjunct to improving post-surgical outcomes needs to be considered more seriously.