Page 127 - DISINVESTMENT AND IMPLEMENTATION OF VISION SCREENING TESTS BASED ON THEIR EFFECTIVENESS

Effectiveness of routine population-wide orthoptic preschool vision screening tests at age 6-24 months in The Netherlands
There was a high response rate from the treating orthoptists (532 out of 771 referrals in the control group and 464 out of 755 referrals in the intervention group) which minimized the lost to follow up. Some information could not be retrieved because: (i) some children were first referred to their general practitioners and they might not have referred the child further to an orthoptist; (ii) parents were unaware of the referral; (iii) parents did not comply with the referral; (iv) some orthoptic clinics changed during the long follow-up.10,11 With no received orthoptic information, we might have missed some amblyopic children. Children, who could not be classified as amblyopic due to two or more failed or insufficient VA measurements at the CHC centre without orthoptic information, hold the highest potential risk to be amblyopic. As this group was similar between groups 234 (4.2%) versus 208 (4.1%) we expect the amount to be the same in both groups. Because only the orthoptic information from the first measurement was analysed, the orthoptic assessment at a young age (i.e. before VA could be measured) might have missed some children with micro strabismus. Moreover, children with high anisometropic amblyopia might have had a micro strabismus which was not recognized at the first orthoptic visit. The high amount of children with bilateral amblyopia could be explained as only the orthoptic information of the first VA measurement was recorded. Therefore, the amblyopia diagnosis was based on the VA before glasses adaptation.
The small difference in type of amblyopia between the groups, slightly more strabis- mus amblyopia and slightly less refractive amblyopia in the control group, could be explained by the age of diagnosis. Children in the control group were diagnosed a bit earlier and because anisometropia tends to increase with age children in the control group were more likely to be classified as amblyopic due to strabismus than amblyopia due to refractive error. Also the same criteria for refractive amblyopia were used for all ages.
The strength of this study is the large sample size, (8% of the Dutch birth rate was included) with a long follow-up (37 722 patient-years exposure time) and high attendance rate. The incidence of amblyopia (3.3% versus 3.1%) is comparable to literature.12
A limitation of the study is that only the referred children had an orthoptic eye examination. Due to the large sample size, it was not possible to provide all children with an orthoptic examination. Most children had two VA measurements (36 and 45 months) at the CHC centres. The observational study by Sloot et al. showed a good performance of the VA measurements at the CHC centres.13 Therefore, children with
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