Page 126 - DISINVESTMENT AND IMPLEMENTATION OF VISION SCREENING TESTS BASED ON THEIR EFFECTIVENESS

CHAPTER 6
DISCUSSION
This study demonstrated that omission of routine preverbal eye screening tests between the age of 6-24 months in the Netherlands did not lead to significant differences in amount of children referred, in total cases of amblyopia detected or in time of detection. Nor was there a significant difference in the severity of the detected amblyopia. The most important reason for referral at age 6-24 months was observed strabismus or a visually apparent eye disorder noticed by the parents. These disorders will be detected regardless of formal vision screening. Strabismus amblyopia was mainly detected before the age VA could be measured. Refractive amblyopia and bilateral amblyopia on the other hand were detected, almost exclusively, with the VA measurements between 36-60 months. Visual acuity measurements at 36-60 months yielded far more amblyopia cases compared to the screening between 6-24 months with even expenses. Only 0.8% from the 3.3% amblyopia in the control group and 0.5% from the 3.1% amblyopia in the intervention group were detected with preverbal screening. More strabismus amblyopia cases were detected in the control group. This difference only became apparent after the VA measurements.
Amblyopia is more responsive to treatment in children younger than seven years of age.9 As there was no significant difference in time to referral and severity of amblyopia, omission of eye screening between 6-24 months does not seem to affect the effectiveness of amblyopia treatment. With the VA measurements at 45 months, children will be referred and receive treatment well before the age of seven. In ongoing research we will assess whether there is a difference in amblyopia treatment received between children referred from the control versus the intervention group.
The positive predictive value (PPV) was low for all screening moments. In the Netherlands, the general health screening is performed by youth health care physicians and nurses, which makes screening much cheaper than screening performed by orthoptists, but might lead to a lower PPV. Another factor that influences the PPV is the low prevalence of amblyopia. For the VA measurements at 45 months the low PPV might be an underestimation because children were already under orthoptic control due to the VA measurements at 36 months. Due to the higher age CHC personnel might have referred children quicker because of fear of missing amblyopia at this age and because they depend more on the VA measurements at 45 months. The high specificity and high negative predictive value can be explained by the large sample size and the low incidence rate of amblyopia.
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