Glasgow Acuity Cards: a new test for the measurement of letter acuity in children

Abstract

Problems with design and format of the traditional Snellen chart have led to the development of alternative charts for the measurement of visual acuity in adults. However, advances in chart design for the measurement of visual acuity in pre-school children have not paralleled those used in adult test charts. Visual acuity can be measured in infants and very young children using behavioural and electrophysiological techniques but clinical measurement of letter acuity tends to commence when the child is old enough to interact and co-operate with the examiner. Charts which are commercially available in the UK for measuring letter acuity in pre-school children (3-5 years old) either use single optotypes or are derivatives of the Snellen format. There is a need for a test of letter acuity for use with this young age group which is accurate, reliable and based upon sound and established design principles. Glasgow Acuity Cards have been designed to include features that should allow change in letter acuity to be detected in pre-school children, especially those undergoing vision therapy training. The test is performed at 3 m and incorporates several design features which have been used previously in adult charts but are new to childrens' test charts. These include: linear progression of letter sizes using a log scale; letters of approximately equal legibility; equal number of letters per line; control of contour interaction; screening cards to determine initial level of acuity. The test is quick and easy to perform and should provide a means of detecting change in letter acuity, with increased confidence.

Vision testing in schools: an evaluation of personnel, tests, and premises

“…One hundred and six children were also tested using a 3 metre linear test, the Glasgow acuity cards. 4 In this test the child again matches letters but is shown a line of four letters at a time to identify, thus increasing the accuracy because of the presence of a crowding eVect. These children were not randomly selected for testing with this additional test, but the testing was performed only in schools where there was time available.…”

Improving the reliability of visual acuity measures in young children

“…The Bailey±Lovie chart and the Early Treatment of Diabetic Retinopathy Study (ETDRS) chart have become`gold standard' measures of visual acuity in clinical research and clinical trials (Ferris and Bailey, 1996). However, these important developments in test chart design have only recently been paralleled in the design of tests used to measure speci®cally the visual acuity of young children (McGraw and Winn, 1993).…”

“…A new visual acuity test (Glasgow Acuity Cards, McGraw and Winn, 1993) has recently been developed which incorporates several key design features used in adult test charts (Bailey and Lovie, 1976) to improve the sensitivity and reliability of visual acuity measurements in young children, and introduces features of particular value in the measurement of visual acuity in amblyopic eyes. In this study the e ects of incorporating such features into letter acuity tests for young children are examined.…”

Visual acuity in children: The development of crowded and single letter acuities

“…This test is designed for accurate measurement of "crowded" visual acuity in children (McGraw & Winn, 1993) and incorporates several features to ease visual acuity testing in young children. The testing distance of 3 m allows better communication and easier testing of children and has no adverse effect on the acuity compared to acuity testing at the standard 6 m distance (Atkinson, Anker, Evans, Hall, & Pimm-Smith, 1988).…”