| Abstract
| - Abstract. Objectives To test the efficacy of treatment for unilateral visual loss detected by preschool vision screening and the extent to which effectiveness varies with initial severity. Design Randomised controlled trial of full treatment with glasses and patching, if required, compared with glasses only or no treatment. Masked assessment of best corrected acuity after one year of follow up. Setting Eight UK eye departments. Participants 177 children aged 3-5 years with mild to moderate unilateral impairment of acuity (6/9 to 6/36) detected by screening. Results Children in the full and glasses treatment groups had incrementally better visual acuity at follow up than children who received no treatment, but the mean treatment effect between full and no treatment was equivalent to only one line on a Snellen chart (0.11 log units; 95% confidence interval 0.050 to 0.171; P < 0.0001). The effects of treatment depended on initial acuity: full treatment showed a substantial effect in the moderate acuity group (6/36 to 6/18 at recruitment) and no significant effect in the mild acuity group (6/9 to 6/12 at recruitment) (P = 0.006 for linear regression interaction term). For 64 children with moderate acuity loss the treatment effect was 0.20 log units, equivalent to one to two lines on a Snellen chart. When all children had received treatment, six months after the end of the trial, there was no significant difference in acuity between the groups. Conclusions Treatment is worth while in children with the poorest acuity, but in children with mild (6/9 to 6/12) unilateral acuity loss there was little benefit. Delay in treatment until the age of 5 did not seem to influence effectiveness.
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