Visual acuity in children: The development of crowded and single letter acuities
Keywords:Visual acuity, crowding, single letter, development, children
Previous research has explored the development of visual acuity in babies and children, and it has been established that the measured acuities are dependent on the methods used to test visual function. In the present study the developmental trends in crowded versus single letter visual acuities were explored. 343 children 5 to 11 years of age, was tested using Glasgow Acuity Cards (GAC), and a significant correlation between binocular visual acuity and age was found using simple regression analysis (y=0.023x + 0.81, r2 = 0.32). Mean values on crowded visual acuity varied between 0.95 ± 0.6 in 5 year olds to 1.08 ± .09 logMAR in 11 year olds. One way ANOVA confirmed the developmental trend (F(1, 341)=160.45, p<0.0001). In a second study, this result were replicated in a smaller group of fully corrected children (regression analysis showed significant development with age, y=0.025x+.86, r2 = 0.429, one way ANOVA: F(1,72) = 54.11, p<0.0001). The repeatability of the GAC was tested using a test-retest strategy, 6 months apart. A significant improvement of monocular visual acuities at the second retest may be explained, at least in part, by the expected development during this period. A single letter acuity test was constructed by matching GAC optotypes. Fiftyt two emmetropic children (mean age 8.21±1.76 yrs) were tested on both tests. Developmental trends were then compared for single and crowded acuities. Linear regressions were F(1,50)=23.87, p=0.0001, y=0.019x+0.915, r2=0.31 for crowded letters and F(1,50)=5.81, p<0.05, y=0.009x+1.07, r2=0.104 for single letters. Repeated measures ANOVA (test * age) showed reliable differences for both main effects. Single letter acuity was found to display a very slight developmental trend, and was better than crowded acuity. When deciding normal values and cut-off limits, one have to take into consideration which test is being used as normative data will not directly translate from one test to another.
Atkinson J. Human visual development over the first 6 months of life. A review and a hypothesis (1984). Human Neurobiology, 3, 61- 74.
Atkinson J, Anker S, Evans C, Hall R & Pimm-Smith E. (1988). Visual acuity testing of young children with the Cambridge Crowding Cards at 3 and 6 m. Acta Ophthalmologica, 66, 505- 508.
Atkinson J, Pimm-Smith E, Evans C, Harding G & Braddick O. (1985). Visual crowding in young children. In Jay B (ed.) Detection and Measurement of Visual Impairment in Pre-verbal children. Documenta Ophthalmologica Proceedings Series, Junk Publishers Series, Boston. 45: 210-211.
Bailey IL & Lovie JE. (1976). New design principles for visual acuity letter charts. American Journal of Optometry & Physiological Optics, 53: 740- 745.
Brown B & Yap MKH. (1995). Differences in visual acuity between the eyes: determination of normal limits in a clinical population. Ophthalmic and Physiological Optics, 15, 136- 169.
Burg A. (1966). Visual acuity as measured by static and dynamic tests: a comparative evaluation. Journal of Applied Psychology, 50, 460- 466.
Chen SI, Chandna A, Norcia AM, Pettet M & Stone D. (2006). The repeatability of best corrected acuity in normal and amblyopic children 4 to 12 years of age. Investigative Opthalmology and Visual Science, 47, 614-619.
Drover JR. Felius J. Cheng CS. Morale SE. Wyatt L & Birch EE. (2008). Normative pediatric visual acuity using single surrounded HOTV optotypes on the Electronic Visual Acuity Tester following the Amblyopia Treatment Study protocol. Journal of AAPOS, 12, 145-149.
Fern KD & Manny RE. (1986). Visual acuity of the preschool child: A review. American Journal of Optometry & Physiological Optics, 63: 319- 345.
Fern KD, Manny RE, Davis JR & Gibson RR. (1986). Contour interaction in the preschool child. American Journal of Optometry & Physiological Optics, 63, 313- 318.
Flom MC, Heath G & Takahashi E. (1963b). Contour interaction and visual resolution: contralateral effects. Science, 142, 979.
Flom MC, Weymouth FW & Kahneman D. (1963a). Visual resolution and contour interaction. Journal of the Optical Society of America, 53, 1026- 1032.
Graham FK, Berman PW & Erhart CB. (1960). Development in pre-school children of the ability to copy forms. Child Development, 31, 339- 359.
Hall DMB (1989). Health for All Children. Oxford University Press, Oxford.
Hohmann A & Haase W. (1982). Development of visual line acuity in humans. Ophthalmic Research, 14, 107- 112.
Jayatunga R, Sonksen PM, Bhide A & Wade A. (1995). Measures of acuity in primary-school children and their ability to detect minor errors of vision. Developmental Medicine and Child Neurology, 37, 515- 517.
Kothe AC & Regan D. (1990). The component of gaze selection/control in the development of visual acuity in children. Optometry and Vision Science, 67, 770- 778.
Levi DM, Carney T. ((2009). Crowding in peripheral vision: why bigger is better. Current Biology, 19, 1988-1993.
McCulloch DL. (1998). The infant patient. Ophthalmic and Physiological Optics, 18, 140- 146.
McGraw PV & Winn B. (1993). Glasgow Acuity Cards: a new test for the measurement of letter acuity in children. Ophthalmic and Physiological Optics, 13, 400- 404.
McGraw PV, Winn B, Gray LS & Elliot DB. (2000). Improving the reliability of visual acuity measures in young children. Ophthalmic and Physiological Optics, 20, 173-184.
Norgett Y & Siderov J. (2011). Crowding in childrenâ€™s visual acuity tests- effect of test dsign and age. Optometry and Vision Science, 88, 920-927.
Salt AT, Sonksen PM, Wade AM & Jayatunga R. (1995). The maturation of linear acuity and compliance with the Sonkseen-Silver acuity system in young children. Developmental Medicine and Child Neurology, 37, 505- 514.
Salt AT, Wade AM, Proffitt R, Heavens S & Sonksen PM (2007). The Sonksen logMAR test of visual acuity: I. Testability and reliability. Journal of AAPOS, 11, 589-596.
Sheridan MD. (1974). What is normal distance vision at five to seven years? Developmental Medicine and Child Neurology, 16, 189- 195.
Simmers AJ, Gray LS & Spowart K. (1997). Screening for amblyopia: a comparison of paediatric letter tests. British Journal of Ophthalmology, 81, 465- 469.
Sonksen PM. Wade AM. Proffitt R. Heavens S. & Salt AT. (2008). The Sonksen logMAR test of viaual acuity: II. Age norms from 2 years 9 months to 8 years. Journal of AAPOS, 12, 18-22.