Visual function thresholds in children

Purpose. The aim of the present study was to establish a range of values fo r individual visual function measurements in Primary 1 schoolchildren. Methods. 93 visually normal children with a mean age of 5.4 +/- 0.3 years w ere recruited with parental consent. Measures of visual acuity obtained inc luded 1) High Contrast (CAT) 2) Low Contrast (LC) 3) Single Letter (SLA) an d 4) Repeat Letter Acuity (RRL). These measurements were randomised and obt ained during the same visit. Hyperacuity thresholds were obtained at a sepa rate visit, using both Vernier and oscillatory motion displacement stimuli (OMDT). Re-test data for all tests was collected from a random sample of 30 children after a period of at least two weeks. Results. For all measures the distribution of scores was found to be normal . All visual acuity scores are in log units. Mean (+/- SD) values for each test were as follows; CAT = 0.11 +/- 0.07; LC = 0.38 +/- 0.08; RRL = 0.04 /- 0.07; SLA = -0.02 +/- 0.09; Vernier threshold = 69 +/- 21 arcsec; OMDT = 60 +/- 9 are sec. The confidence limits of the test-retest discrepancies w ere as follows; CAT = +/- 0.05, LC = +/- 0.07; RRL = +/- 0.04; SLA = +/- 0. 04; Vernier = +/- 17 arcsec; OMDT = +/- 6 arcsec. The confidence limits of the interocular discrepancies were as follows; CAT = +/- 0.08; LC = +/- 0.0 8; RRL = +/- 0.08; SLA = +/- 0.11; Vernier = +/- 14 arcsec; OMDT = +/- 11 a rcsec. Conclusions. To fully describe an individual's visual capacity it is import ant that new tests of visual function are developed based on emerging knowl edge of visual physiology. In this study confidence limits can be construct ed for each visual function measure, test-retest and interocular discrepanc ies using the normal distributions found above. This will provide the clini cian with further age-matched values and contribute to our understanding of functional visual development.