A study recently published in JAMA Ophthalmology investigated the persistence of myopic shift following overminus spectacle treatment in children.
Give me some background first.
Intermittent exotropia (IXT) is the most common form of divergent strabismus in children, and overminus lens therapy is a common nonsurgical treatment option.
By using more minus power than cycloplegic refractive error, clinicians can work to temporarily control IXT in children. If controlled well, sometimes patients can be weaned off and can possibly forgo further treatment.
Go on…
A previous randomized control trial (RCT) compared overminus and non-overminus spectacles in children with IXT. Researchers found that after 12 months of overminus spectacles (-2.50 diopters (D)), IXT distance control was improved.
However, they also found that the treatment was associated with myopic shift. Thus, researchers conducted an 18-month extension study evaluating the myopic shift.
Let’s hear more about the previous study.
The Trial of Overminus Spectacle Therapy for Intermittent Exotropia (NCT02807350) cohort randomized a total of 386 participants to either overminus or non-overminus spectacles.. Characteristics of the participants included:
- Children aged 3 to 10
- IXT of 15 prism diopters or more
- Baseline spherical equivalent refractive error (SER) range: -6D to +1D
Now, onto the study at hand.
Participants were asked to participate in the post-RCT study that included follow-ups at 24 and 36 months past randomization.
A total of 205 of the original participants participated in the follow-up study through 36 months. At these time points, the following tests were performed:
- IXT assessments at the beginning, middle, and end
- Cover-uncover test
- Prism and alternate cover test both at distance and near
- Cycloplegic retinoscopy
What measurements were recorded?
The following measurements were taken at each follow-up point:
- Cycloplegic autorefraction
- Axial length
- Flat corneal curvature
- Anterior chamber depth
- Lens thickness
Findings?
Statistical analysis was performed to compare baseline and follow-up levels.
When compared to the baseline SER myopic shift, the overminus group had a greater mean than the non-overminus at both 24 and 36 months (-0.61D vs. -0.14D and -0.74D vs. -0.44D, respectively).
Tell me more.
When comparing myopic shift at 36 months, 26.8% of the overminus group had over 1.00 D of myopic shift, and just 15% of the non-overminus group was at this level.
However, between 12 and 36 months, there was no difference in mean myopic shift between the overminus and non-overminus groups (-0.34D and -0.36D, respectively).
Anything else?
The overminus group exhibited twice the risk of myopic progression above 1.00 D over 3 years than the non-overminus group. Those that had baseline myopia demonstrated a greater difference in myopic shift.
Expert input on this: These findings suggest that “children with IXT and baseline hyperopia of 0.50 to 1.00 D do not have significant risk for a myopic shift greater than 1.00 D with overminus lens treatment over 36 months,” according to the study authors.
Expert opinion?
Per the authors, the study demonstrated that “myopic shift at 1 year persisted but did not increase further during the 2 years after the start of weaning and discontinuation of overminus treatment.”
They continued: “Thus, the same treatment group difference initially observed at 12 months was still present at 3 years. These findings suggest that cessation of the original overminus lens treatment neither exacerbated nor lessened the myopic shift.”
Limitations?
A key limitation of this study was that only 53% of the original cohort completed the 36-month follow-up, opening the door to bias. Additionally, slightly different proportions of overminus and non-overminus groups participated in different levels of follow-up.
Thus, the authors recommend caution in interpreting subgroup analyses due to the small sample sizes in SER baseline subgroups.
Take home.
The authors concluded: “Over 3 years, 1 year of overminus treatment was associated
with a 0.33-D increase in mean myopic shift and approximately twice the risk of having a myopic shift of 1.00 D or greater.”
And lastly?
Ultimately, they suggested that “the risk of myopic shift should be discussed when considering
overminus lens treatment for children with IXT, particularly for those already myopic.”