Observational Study of Optical Correction for Strabismic Amblyopia in Children 3 to <7 Years Old
Condition: Amblyopia
MeSH terms: Amblyopia
Study type: Observational

Summary: 
      This study will evaluate the effectiveness of refractive correction alone for the treatment
      of previously untreated strabismic or combined-mechanism amblyopia in children 3 to <7 years
      old with visual acuity of 20/40 to 20/400
    

Detailed description: 
      This study will evaluate the effectiveness of refractive correction alone for the treatment
      of previously untreated strabismic or combined-mechanism amblyopia in children 3 to <7 years
      old with visual acuity of 20/40 to 20/400.

      A recently completed PEDIG study (ATS5) found that in 3 to < 7-year-old children with
      previously untreated anisometropic amblyopia, refractive correction alone improved visual
      acuity by 2 or more lines in 77% of the patients and amblyopia resolved in at least one third
      of the patients. These results supported previous observations from retrospective and pilot
      studies as well as Stewart et al's prospective report on 18 children with anisometropic
      amblyopia whose visual acuity improved after treatment with spectacle correction only.

      Improvement in amblyopic eye visual acuity from treatment with optimum refractive correction
      in cases of anisometropic amblyopia is plausible because the refractive correction treats the
      underlying amblyogenic condition (i.e., uncorrected unequal refractive error) by providing
      retinal images of more similar clarity, size, and contrast. Elimination of the dissimilar
      retinal images, which may act as barriers to normal visual input, allows the amblyopic eye to
      receive appropriate visual stimulation. In contrast, visual acuity improvement with
      refractive correction alone in cases of amblyopia associated with strabismus is not expected
      to occur when the refractive correction does not completely eliminate the strabismus and
      restore fusion. In such cases, the underlying amblyogenic factor of a manifest ocular
      deviation remains; consequently, active cortical inhibition is presumably still present.
      Nonetheless, Stewart and colleagues recently reported finding gains in amblyopic eye visual
      acuity of children with strabismic and combined-mechanism amblyopia after a period of
      treatment with refractive correction alone. The PEDIG also observed this to occur in a
      subgroup of children with previously untreated strabismic and combined-mechanism amblyopia in
      a recent study. Amblyopic eye acuity improved by >= 2 lines from spectacle-corrected baseline
      acuity in 9 (75%; 95% CI = 43% - 95%) of the 12 patients with strabismic amblyopia and in 9
      (69%, 95% CI = 39% - 91%) of the 13 patients with combined-mechanism amblyopia. Mean change
      from baseline to maximum improvement was 2.2 +- 1.8 and 2.6 +- 2.0 lines, respectively. These
      results are similar to those of Stewart and colleagues who reported visual acuity improvement
      averaging 3.0 lines in 16 children with strabismic amblyopia and 1.9 lines in 31 children
      with combined-mechanism amblyopia.

      Although our results support the suggestion of Stewart et al. that strabismic amblyopia can
      improve with spectacle correction alone, they are not conclusive because both studies had
      small numbers of patients. Also, our classification of strabismus was based on alignment
      without refractive correction. Thus, a larger controlled study is needed to confirm or refute
      these findings in patients with strabismic and combined-mechanism amblyopia.

      The ideal study design to answer the question of whether spectacles alone can significantly
      improve amblyopic eye visual acuity in strabismic children is a randomized trial with a
      control group who does not receive optical correction. However, most pediatric eye care
      providers would be reluctant to randomize esotropic children with hyperopic refractive error
      to a control group of no optical correction because of the likelihood of some children having
      accommodative esotropia, which would necessitate that hyperopic spectacles be prescribed. The
      number of esotropic amblyopes without an accommodative component is sufficiently few to make
      a randomized trial not feasible. Therefore, we have chosen to perform an observational study
      with a large number of children with pure strabismic and combined-mechanism amblyopia in
      order to evaluate the effect of refractive correction in this population of patients.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Community Sample
      
Keywords: Amblyopia associated with strabismus; Refractive error