Child Visual Acuity Standards

Visual acuity in children is essential in the detection and monitoring of visual problems. A standardised system for acuity testing is also needed for preschool and young aged children to enhance testability and reliability of visual screening. A chart specifically designed for VA assessment for the paediatric population has been included in the Optonet Vision Unit. The chart consists of single lines of 5 symmetrical letters with uniform contour interaction, according to international guidelines.

Linear visual acuity with symmetrical letters (instead of symbols) has been shown to constitute a reliable and testable method of VA measurement in children from the age of around 2.5 years to 7 years.1,2,3,4 The task of identifying those letters (with a matching card) is similar to that used for adult standard VA testing, therefore, the use of VA charts with symmetrical letters for children will ease their transition to adult testing, and also facilitates comparison with adult values. The letters O, X, H, T, U and V5,1,3 are easy to match, and have been incorporated to children’s VA charts in the vision unit.

Broken Glasses Test

The Optonet Vision Unit also includes a new test (the “Broken Glasses” test) to evaluate acuity in the preschool population.  The “Broken Glasses” test uses Landolt C optotypes, which have traditionally been considered as the standard in the measurement of VA, and the reference against which the rest of optotypes should be compare.6 The optotypes are presented in a modified, four-choice format, which substantially improves reliability over an older (Broken Wheel) test which uses a two-choice format.7

The test consists of 4 smiling faces wearing glasses, three of which have complete eyeglass rings, while the rings of the fourth face are open. The open rings in the face with “broken glasses” are actually calibrated Landolt Cs.  All the rings on the screen have the same size and stroke thickness. The strokes on the face and cap guarantee sufficient contour interaction for improved amblyopia detection in the preschool population. Four simple colours have been used for the caps: red, blue, green and yellow.

Visual acuity date are being collected through the Optonet Project from different practices, in order to generate normative curves that may be useful to assess normal visual development of infants and young children of different ethnicities around the world.

This study is expected to provide Child Growth Standards (CVAS) to establish the normative model for normal physiological VA development from 2.5 years to 7 years of age.

The Optonet Vision Unit allows children vision screenings and monitoring to be carried out remotely. It should be noted that children from the most deprived backgrounds and those from unstable homes were more likely to fail preschool vision screening.8

References

1. McGraw, P. V. & Winn, B. Glasgow Acuity Cards: a new test for the measurement of letter acuity in children. Ophthalmic Physiol. Opt. J. Br. Coll. Ophthalmic Opt. Optom. 13, 400–404 (1993).
2. McGraw, P. V., Winn, B., Gray, L. S. & Elliott, D. B. Improving the reliability of visual acuity measures in young children. Ophthalmic Physiol. Opt. J. Br. Coll. Ophthalmic Opt. Optom. 20, 173–84 (2000).
3. Salt, A. T., Wade, A. M., Proffitt, R., Heavens, S. & Sonksen, P. M. The Sonksen logMAR Test of Visual Acuity: I. Testability and reliability. J. AAPOS Off. Publ. Am. Assoc. Pediatr. Ophthalmol. Strabismus Am. Assoc. Pediatr. Ophthalmol. Strabismus 11, 589–96 (2007).
4. Sonksen, P. M., Wade, A. M., Proffitt, R., Heavens, S. & Salt, A. T. The Sonksen logMAR test of visual acuity: II. Age norms from 2 years 9 months to 8 years. J. AAPOS Off. Publ. Am. Assoc. Pediatr. Ophthalmol. Strabismus Am. Assoc. Pediatr. Ophthalmol. Strabismus 12, 18–22 (2008).
5. Sheridan, M. D. What is normal distance vision at five to seven years? Dev. Med. Child Neurol. 16, 189–195 (1974).
6. Universale, C. O. & Committee, V. F. Visual Acuity Measurement Standard – International Council of Ophthalmology. 1–18 (1988).
7. Richman, J. E., Petito, G. T. & Cron, M. T. Broken wheel acuity test: a new and valid test for preschool and exceptional children. J. Am. Optom. Assoc. 55, 561–565 (1984).
8. O’Colmain U, Low L, Gilmour C, et alVision screening in children: a retrospective study of social and demographic factors with regards to visual outcomesBritish Journal of Ophthalmology 2016;100:1109-1113.

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