Page 64 - DISINVESTMENT AND IMPLEMENTATION OF VISION SCREENING TESTS BASED ON THEIR EFFECTIVENESS

CHAPTER 3
RESULTS
The estimation of the incidence curves per amblyopia type resulted in four graphs each with an upper and lower estimate, based on approximation of the observational data in conjunction with the experts’ estimations and literature.6–8 For upper and lower estimates of incidence curves, we consulted several orthoptists, who are involved in the treatment of children with amblyopia, and strabismologists. All agreed that amblyopia does not develop before the age of 3 months, or after the age of 5 years. Elston and Timms have previously shown that the lower age limit before the start of the sensitive period for development of amblyopia is at least 4–6 weeks after birth.6 Basic neurophysiologic research on amblyopia performed by Hubel and Wiesel showed that there is an upper age limit for the development of amblyopia in animals.7 Keech and Kutschke found that no human subject developed amblyopia after age 6 years.8 The model simulated 10 incidence curves per amblyopia type which, together with the cumulative number of cases found per screen, produced the plots shown in Figure 2. The incidences of combined-mechanism amblyopia and refractive amblyopia were highest (between 30 and 40 cases per 2964 children), the incidence of pure strabismic amblyopia was lower (less than 20 cases per 2964 children) and the incidence of deprivation amblyopia was lowest (less than 20 cases per 2964 children).
Figure 2. The estimated cumulative incidence per amblyopia type for a cohort of 2964 children.
Dots represent the detected amblyopia cases in the RAMSES study by screening only (cumulative). The upper black lines represent the upper estimate and the lower grey line represents the lower estimate of the incidence curves.
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