Page 61 - DISINVESTMENT AND IMPLEMENTATION OF VISION SCREENING TESTS BASED ON THEIR EFFECTIVENESS

The effect of omitting an early population-based vision screen in the Netherlands: A micro-simulation model approach
A major problem in developing this model is that the true incidence curves of the disease are unknown. It is known that amblyopia does not exist at birth, but may develop after age 3 months in cases where one eye is used less for vision. Generally, amblyopia does not develop after age 6. Refractive amblyopia may develop at an older age than strabismic amblyopia and can be treated at an older age.6–8 The incidence curves for refractive, strabismic, combined-mechanism, and deprivation amblyopia were derived by approximation of the observational data in conjunction with experts’ estimations. Data collected during the RAMSES study, in which the prevalence of amblyopia between ages 0 and 7 years was 3.4%, were used.4
In the RAMSES study, 100 amblyopia cases were found, 73 with a positive screening and 27 with no positive screening. Of the 73 cases with a positive screening, 60 had been detected by screening, and 12 were detected by the parents but were positively screened later on. In one case, it was unclear whether the child visited the ophthalmology department after the positive test. Four children had been unsuccessfully referred. All 100 amblyopia cases had been differentiated by amblyopia type, and a further differentiation in age of detection for each of the four types was made. We used the combined data about the cause of amblyopia with the screen at which each case of amblyopia was detected (Table 1).
Table 1. Number of tests and detected amblyopia cases in the RAMSES study differentiated to the four main causes of amblyopia and the screen at which each case was detected.
Age of positive screening
6–9 Months
14 Months
24 Months
36 Months
45–54 Months
60 Months
No positive screen
Sum
Combined- mechanism
Unknown Total
type amblyopia
0 8 0 5
0 9 1 14 1 25 0 12 0 27
2 100
Tests Strabismus Refractive
Deprivation
3272 3297
2982
2659
2457
2824
31 1 0
1 0 54 3 15 08 6 14
4 0 2 2
7 1 4 0 5 1 3 1 5 2
19 42 30 7
Note: The screening exams before 6 months of age were not included in the RAMSES study.
No positive screen means that the child was detected outside of screening, for example because parents had noticed abnormalities and had gone to their General Practitioner or to the hospital
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