Page 180 - DISINVESTMENT AND IMPLEMENTATION OF VISION SCREENING TESTS BASED ON THEIR EFFECTIVENESS

CHAPTER 9
In the OVAS study we found that at the age of 6-9 months most children were referred by CHC physicians to an orthoptist or ophthalmologist because of observed strabismus or visually apparent disorders, that was most often noticed first by the parents. At 6-9 months the detection rate of amblyopia was very low and amblyopia was caused by strabismus or strabismus combined with refractive disorder, none solely by refractive disorder, confirming the results of the RAMSES study. The total study population consisted of 10,622 children with 37,722 patient-years of on study exposure time and a 5 year follow-up. At the age of 6-24 months strabismus amblyopia and visually apparent eye disorders were mainly detected by the parents and were detected regardless of formal vision screening. Omission of routine preverbal eye screening tests between the age of 6-24 months did not lead to significant differences in amount of children referred, in total number of cases of amblyopia detected or in the severity of the detected amblyopia. Visual acuity measurements at 3-5 years yielded 3.2 times more amblyopia cases as compared to the screening between 6-24 months. Refractive amblyopia and bilateral amblyopia were detected almost exclusively by measurement of VA at the age of 36-60 months. The small difference in type of amblyopia between the groups, slightly more strabismus amblyopia and slightly less refractive amblyopia in the control group, could be explained by the age of diagnosis of amblyopia: 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 amblyopic due to refractive error. These results have led to disinvestment of preverbal vision screening with orthoptic tests in the Netherlands as formulated in the revised CHC vision screening guideline.9
With the VA measurements, children will be referred and receive treatment well before the age of seven.10 The quality of the VA measurements is of high importance to detect children in time for treatment. In the previous CHC vision screening guideline VA was measured by CHC physicians at 36 months with the Amsterdam Picture Chart (APK) and with Landolt C optotypes at 45 and 60 months according to thresholds formulated in the guideline. Visual acuity measurements at 36 months with the Amsterdam Picture Chart (APK) were analysed further because many considered the VA measurements with the APK as unreliable. Others believed that the percentage of failed VA measurements at the age of 36 months was too high. The latter proved to be correct. Visual acuity was measured in 8,661 eligible children from the OVAS sequential birth cohorts at 36 months. The measured VA was insufficient in 15.5% of children, whereas in another 16.6% the measurement failed altogether. If CHC doctors and nurses would have acted completely according to the CHC guideline, 32,1% of VA tests at 36
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