Stewart et. al. reported that refractive correction alone can be effective in treating young children with previously untreated strabismic amblyopia, even in the absence of anisometropia.1
In 16 patients with strabismic amblyopia treated with spectacles alone, they found amblyopic eye acuity improved a mean of 3.0 lines over an 18-week period. This was somewhat surprising because, in such cases, the amblyopia is presumably due to the ocular misalignment, which most often would not be fully corrected with spectacles alone. We reviewed data from our recent prospective study2
to determine if our results were consistent with those of Stewart and coworkers.
This study was registered at ClinicalTrials.gov
The full study protocol is available online.4
The protocol and HIPAA-compliant informed consent forms were approved by the respective institutional review boards and the parent or guardian of each study patient gave written informed consent.
As a run-in phase to a randomized trial of patching treatment for amblyopia,5
spectacles were prescribed to correct refractive error, no other amblyopia treatment was prescribed, and patients were followed until visual acuity appeared stable. Results in patients with previously untreated anisometropic amblyopia have been reported2
. Data were available for 12 patients (75% female, 83% white, mean age 5.0±0.9 years) with previously untreated strabismic amblyopia who had a constant strabismus at distance and near and anisometropia of ≤0.75 D in spherical equivalent or ≤1.25 D in astigmatism (). Spectacle-corrected monocular distance visual acuity was measured using the electronic Amblyopia Treatment Study HOTV protocol6, 7
at baseline and every 5 (±1) weeks provided amblyopic eye acuity had improved at least 1 line (0.1 logMAR) from the prior visit and remained at least 1 line worse than sound eye acuity. Patients whose acuity did not improve at least 1 line from the prior visit but still had ≥2 lines of interocular difference (IOD) entered a randomized trial.5
Those randomized to the control group continued spectacles if needed but did not start other therapy, and provide additional data on the course of the amblyopia treated with spectacles alone.
Baseline Clinical Characteristics and Change in Amblyopic Eye Visual Acuity
Among the 12 strabismic patients, during the spectacles-only phase of follow up, amblyopic eye acuity improved by ≥ 2 lines from spectacle-corrected baseline acuity in 9 (75%) resolving in 3 (IOD ≤ 1 line), . Mean change from baseline to maximum improvement was 2.2 ± 1.8 lines. Improvement continued for up to 25 weeks. Additional amblyopia improvement ≥1 line occurred, though amblyopia did not resolve, in 3 of the 5 patients with residual amblyopia who entered the subsequent randomized trial as controls.
Improvement in Amblyopic Eye Visual Acuity and Resolution of Amblyopia Stratified by Degree of Refractive Error in Amblyopic Eye
Our results support the suggestion of Stewart et al.1
that strabismic amblyopia can improve and even resolve with spectacle correction alone. Although the results are consistent, they are not conclusive, because neither study had a concurrent control group and both had small numbers of patients. It is not possible to rule out the possibility that change in strabismus angle, learning effect, age effect, regression to the mean, or chance could account for some of the observed improvement. Larger studies with concurrent controls are needed to confirm or refute these findings.