Amblyopia screening effectiveness at 3–4 years old: a cohort study

Abstract

ObjectiveTo study the effectiveness of amblyopia screening at ages 3–4.Methods and AnalysisFrom a population with no previous screening, a cohort of 2300 children with 3–4 years old attending school (91% of children this age attend school in Portugal), were submitted to a complete ophthalmological evaluation. Amblyopia was diagnosed, treated and followed. Amblyopia prevalence, treatment effectiveness, absolute risk reduction (ARR), number needed to screen (NNS) and relative risk reduction (RRR) were estimated.ResultsPast/present history of amblyopia was higher than 3.1%–4.2%, depending on amblyopia definition normatives. Screening at age 3–4, had estimated ARR=2.09% (95% CI 1.50% to 2.68%) with a reduced risk of amblyopia in adulthood of 87% (RRR). NNS was 47.8 (95% CI 37.3 to 66.7). Treatment effectiveness of new diagnosis was 88% (83% if we include children already followed). 91% of new amblyopia diagnoses were refractive (of which 100% surpassed amblyopia Multi-Ethnic Pediatric Eye Disease Study criteria after treatment), while most strabismic amblyopias were already treated or undertreatment. Only 30% of children with refractive amblyopia risk factors that were not followed by an ophthalmologist, ended up having amblyopia at age 3–4. Eye patch was needed equally in new-diagnosis versus treated-earlier refractive amblyopia.ConclusionsScreening amblyopia in a whole-population setting at age 3–4 is highly effective. For each 48 children screened at age 3–4, one amblyopia is estimated to be prevented in the future (NNS). Screening earlier may lead to overdiagnosis and overtreatments: Treating all new diagnosis before age 3–4 would have a maximal difference in ARR of 0.3%, with the possible burden of as much as 70% children being unnecessary treated before age 3–4.Involving primary care, with policies for timely referral of suspicious/high-risk preverbal children, plus whole screening at age 3–4 seems a rational/effective way of controlling amblyopia.

Prediction and cost-effectiveness comparison of amblyopia screening methods at ages 3–4 years

“…18 Diagnosing ARFs, as in most current studies, 2–4 leads to diagnosis’ overestimation and biased screening effectiveness indicators. 14…”

“…That is not surprising as those groups have higher prevalence of ARFs and amblyopia, leading the global costs divided per case-detected to be more cost-effective. As stated by the authors, “we should be aware that in Germany, a high percentage of amblyopia cases had already been identified before age 3–4 yo, making it not possible to know if it would be economically attractive to screen at age 3–4 if no previous screening in earlier ages had been taken.” Furthermore, for cost-effectiveness analyses, treated-cases (as we used in this study, based in our treatment efficacy 14 ) are more accurate/interesting outcomes than detected-cases, and there is still scarce information about treatment effectiveness of detected cases when amblyopia screening takes place at age 3–4, with no previous screening.…”

“…There are important limitations to be kept in mind: (1) we assumed treatment efficacy rate was the same as from the previous cohort. 14 In 2012, a study for the Vision Cost-effectiveness Study Group, 23 used treatment efficacy of 66% at 3–4 yo (defined as BCVA ⩾ 0.66) to compare different screening strategies. In our cohort, 14 treatment efficacy was 87.5% (defined as BCVA ⩾ 0.7); (2) we assumed that amblyopia new diagnosis at age 3–4 would not recur after treatment; (3) strabismus, either manifest or easily triggered, was diagnosed by pediatric ophthalmologists that may be more experienced than a less-experienced screener.…”

“…14 In 2012, a study for the Vision Cost-effectiveness Study Group, 23 used treatment efficacy of 66% at 3–4 yo (defined as BCVA ⩾ 0.66) to compare different screening strategies. In our cohort, 14 treatment efficacy was 87.5% (defined as BCVA ⩾ 0.7); (2) we assumed that amblyopia new diagnosis at age 3–4 would not recur after treatment; (3) strabismus, either manifest or easily triggered, was diagnosed by pediatric ophthalmologists that may be more experienced than a less-experienced screener. Nevertheless, considering only manifest strabismus, we created a new variable called manifest-strabismus in M1 (revealed as a separate factor in EFA, p < 0.001), that was also not a predictor ( p > 0.05).…”

“…Methodology of each test performed in M1 and M2, as well as criteria for cycloplegia was described earlier. 13,14…”