Page 59 - 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
INTRODUCTION
In most vision screening programmes, visual acuity (VA) is measured at age 3–6 years. In the Netherlands, VA measurement is preceded by primarily orthoptic examination to detect visual disorders on four occasions between age 0 and 24 months. At 0–4 months, screening consists of inspection of the eye, pupillary reflexes, and examination of the red fundus reflex, to assess media opacities. At the three screening examinations between 6 and 24 months, tests also include corneal reflexes of a light held by the examiner (Hirschberg test), cover test, alternating cover test, eye motility, and quality of ocular pursuit movement (appendix table).1–3 VA is measured at 36 months with the Amsterdam Picture Chart, and at 45 months with the Landolt-C chart.3
The four main types of amblyopia are refractive amblyopia due to anisometropia (unequal strength of glasses), strabismic amblyopia due to misalignment of the eyes, combined-mechanism amblyopia (a combination of misalignment and unequal strength of glasses) and, rarely, deprivation amblyopia due, for example, to congenital cataract or retinoblastoma. Strabismic amblyopia can be noticed by the parents, but refractive amblyopia is not externally apparent, and is often not found until VA is measured.
In the Rotterdam Amblyopia Screening Effectiveness Study (RAMSES)4,5 4624 children born in Rotterdam between September 1996 and May 1997 were followed for 7 years, through all routine vision screening examinations (0–4, 6–9, 14, 24, 36, 45, and 54–60 months) and diagnostic follow-up. Of the 3897 children still living in Rotterdam at age 7, 2964 underwent the final orthoptic study examination. Amblyopia had been diagnosed in 100 children (3.4%). Screening between 6 and 24 months of age contributed little to the detection of refractive amblyopia.4,5
If detailed data are available, the impact of omission or introduction of a single screen can be calculated, but this is difficult if that screen is part of a programme consisting of consecutive screens. To calculate the impact of omission of parts of the early vision screening, we formulated a model, inputting these data.
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