Test-retest reproducibility of accommodative facility measures in primary school children

Abstract

Background: To determine the test-retest reproducibility of accommodative facility (AF) measures in an unselected sample of UK primary school children. Methods: Using 2.00 DS flippers and a viewing distance of 40 cm, AF was measured in 136 children (range 4–12 years, average 8.1 2.1) by five testers on three occasions (average interval between successive tests: eight days, range 1–21 days). On each occasion, AF was measured monocularly and binocularly, for two minutes. Full datasets were obtained in 111 children (81.6 per cent). Results: Intra-individual variation in AF was large (standard deviation [SD] = 3.8 cycles per minute [cpm]) and there was variation due to the identity of the tester (SD = 1.6 cpm). On average, AF was greater: (i) in monocular compared to binocular testing (by 1.4 cpm, p < 0.001); (ii) in the second minute of testing compared to the first (by 1.3 cpm, p < 0.001);(iii) in older compared to younger children (for example, AF for 4/5-year-olds was 3.3 cpm lower than in children ≥10 years old, p = 0.009); and (iv) on subsequent testing occasions (for example, visit-2 AF was 2.0 cpm higher than visit-1 AF, p < 0.001). After the first minute of testing at visit-1, only 36.9 per cent of children exceeded published normative values for AF (≥11 cpm monocularly and≥8 cpm binocularly), but this rose to 83.8 per cent after the third test. Using less stringent pass criteria (≥6 cpm monocularly and≥3 cpm binocularly), the equivalent figures were 82.9 and 96.4 per cent, respectively. Reduced AF did not co-exist with abnormal near point of accommodation or reduced visual acuity. Conclusions: The results reveal considerable intra-individual variability in raw AF measures in children. When the results are considered as pass/fail, children who initially exhibit normal AF continued to do so on repeat testing. Conversely, the vast majority of children with initially reduced AF exhibit normal performance on repeat testing. Using established pass/fail criteria, the prevalence of persistently reduced AF in this sample is 3.6 per cent.