Long-term follow-up of an amblyopia treatment study: change in visual acuity 15 years after occlusion therapy

To determine change in visual acuity (VA) in the population of a previous amblyopia treatment study (Loudon 2006) and assess risk factors for VA decrease.

Subjects treated between 2001 and 2003 were contacted between December 2015 and July 2017. Orthoptic examination was conducted under controlled circumstances and included subjective refraction, best corrected VA, reading acuity, binocular vision, retinal fixation, cover-uncover and alternating cover test. As a measure for degree of amblyopia, InterOcular VA Difference (IOD) at the end of occlusion therapy was compared with IOD at the follow-up examination using Wilcoxon's signed-rank test. Regression analysis was conducted to determine the influence of clinical and socio-economic factors on changes in IOD.

Out of 303 subjects from the original study, 208 were contacted successfully, 59 refused and 15 were excluded because of non-amblyopic cause of visual impairment. Mean IOD at end of therapy (mean age 6.4 years) was 0.11 ± 0.16 logMAR, and IOD at follow-up examination (mean age 18.3 years) was 0.09 ± 0.21 logMAR; this difference was not significant (p = 0.054). Degree of anisometropia (p = 0.008; univariable analysis), increasing anisometropia (p = 0.009; multivariable), eccentric fixation (p < 0.001; univariable and multivariable); large IOD (p < 0.001; univariable and multivariable) and non-compliance during therapy (p = 0.028; univariable) were associated with IOD increase.

Long-term results of occlusion therapy were good. High or increasing anisometropia, eccentric fixation and non-compliance during occlusion therapy were associated with long-term VA decrease. Subjects with poor initial VA had a larger increase despite little patching, but often showed long-term VA decrease.