Subthreshold Amblyopia: Characterization of a New Cohort.

Purpose: Published studies of amblyopia include only patients with visual acuity (VA) worse than 20/40 in one or both eyes. The purpose of this study is to evaluate patients diagnosed and treated as amblyopic despite not meeting traditional VA criteria for amblyopia.

Design: Retrospective clinical cohort study.

Methods: Setting: Institutional practice.

Patient Population: All patients diagnosed with amblyopia at Boston Children's Hospital between 2010 and 2014.

Inclusion Criteria: VA better than 20/40 but not correctable to 20/20 in one or both eyes; age 2 to 12 years.

Observations: Demographics, VA, baseline characteristics.

Outcome Measures: Resolution, defined as VA 20/20 in both eyes; stereopsis at the last follow-up.

Results: Of 2311 patients reviewed, 464 (20.1%) had subthreshold amblyopia. A majority (61.7%) had an amblyogenic factor, most commonly anisometropia (32.8%). Patients were followed for a median of 3.1 years; nearly all (97.5%) were treated. Of 318 patients who returned for follow-up, 47.8% achieved resolution, including 55.7% of treatment-naïve patients, and 62.5% (5 of 8 patients) offered observation alone. Median stereopsis improved by 0.4 log units in those who achieved resolution, with no change in those with persistent amblyopia. In the multivariate analysis, a longer length of follow-up was significantly associated with resolution of subthreshold amblyopia (odds ratio: 1.38; 95% confidence interval: 1.22-1.57, P < .001).

Conclusions: Patients with subthreshold amblyopia represent a sizeable cohort in real-world amblyopia practice. When offered treatment, half achieved 20/20 vision in both eyes with improved stereopsis as well. Further studies are needed to assess whether observation alone would result in similar outcomes.