Page 142 - DISINVESTMENT AND IMPLEMENTATION OF VISION SCREENING TESTS BASED ON THEIR EFFECTIVENESS

CHAPTER 7
DISCUSSION
In this birth cohort study, measured VA was insufficient in 15.5% of the children, while the VA measurement failed in another 16.6% of the children, although parents had practised the APK picture optotypes at home with their children in advance.
One could argue that the rate of failed VA measurements would have been lower when using the Lea symbols, but in a systematic study by Becker et al.,5 it was shown that the failure rate using Lea symbols in general-population screening was even higher than in our study: 44% at the age of 31-36 months and 24% at the age of 37-48 months. In that study, the failure rates were much lower for VA measurements when carried out by orthoptists.5 To have VA measured in all children in the Netherlands by orthoptists would be prohibitively expensive, however. In a Swedish study, measurement of VA using both HOTV and Lea symbols at 36 months and 48 months was evaluated. For both charts, at the age of 36 months, the test failed in 20% of the children apart from the children who did not reach the threshold, as compared to around 10% at the age of 48 months.9
As compared with the Lea Symbols and HOTV, the failure rate of the APK in our study at the age of 36 months is only slightly better, but still too high for it to be used to measure VA in general screening at 36 months. If 16.6% of the VA measurements fails and another 15.5% of the children does not reach the VA threshold, 32.1% should either be retested after six weeks or referred according to the Dutch guideline. For screening in the general population this becomes prohibitively expensive.
In addition, it seems possible that the large number of failed measurements and of measurements with insufficient VA may have kept YHC physicians and nurses from referring children in accordance with the Dutch vision screening guideline at the age of 36 months. It has been found previously by Tjiam et al. that, in some cases, YHC physicians or nurses deviate from the Dutch guideline, when they consider a repeat measurement as unlikely to be successful, for instance when caused by a language barrier.10
Accordingly, YHC physicians and nurses were more inclined to refer a child when the measurement of VA was insufficient as compared to a failed measurement of VA. This is evident from the number of children who were not referred after two failed measurements, 150 (69.4%) of 216 children. According to notes in the records, in at least half of the children with two failed measurements, instead of referral, the decision
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