The effect of omitting an early population-based vision screen in the Netherlands: A micro-simulation model approach.

Objective: To estimate the effect of omitting an individual screen from a child vision screening programme on the detection of amblyopia in the Netherlands. A previous study (Rotterdam Amblyopia Screening Effectiveness Study) suggested that the three screens carried out between 6 and 24 months contributed little. Methods: We developed a micro-simulation model that approximated the birth-cohort data from the previous study, in which 2964 children had completed follow-up at age 7, and 100 amblyopia cases were detected. Detailed data on screens, referrals, and orthoptic follow-up, including the cause of amblyopia, were available. The model predicted the number of amblyopia cases detected for each screen and for the entire screening programme, and the effect of omitting screens. Incidence curves for all types of amblyopia caused by strabismus, refractive anomalies or by both were estimated by approximation of the observational data, in conjunction with experts' estimations and the literature. Results: We calculated mean actual sensitivity per screen per type of amblyopia, and the effect per screen. Screening at 24 months was found to be least effective. The impact on the screening programme, estimated by summing the effectiveness per screen, omitting the 24-month screen, was a reduction of 3.4% (57 vs. 59 cases) in the number of detected cases of amblyopia at age 5. Conclusion: The effectiveness of the Dutch vision screening programme would hardly be affected by omission of the 24-month screening examination. A disinvestment study is warranted.