The Sonksen logMAR Test of Visual Acuity: I. Testability and reliability.

Purpose: To develop a standardized logMAR test of visual acuity for young children and establish testability and reliability.

Methods: Two thousand nine hundred ninety-one children, aged 2 to 8 years 6 months, from a population sample of 4671 were recruited from schools and preschool facilities and tested. Ability to name or match letters, accept occlusion, and achieve binocular single and binocular and monocular measures of linear visual acuity were recorded. Inter- and intratester reliability was assessed for a random selection of 215 children.

Results: Two thousand nine hundred seventy-four (99.4%) matched or named letters, 2966 (99%) achieved binocular single, 2940 (98%) achieved binocular linear, and 2807 (94%) achieved monocular linear (for both eyes) measures. Binocular linear measures were achieved in 50% aged less than 3 years, 80% aged 3 to 3(1/2), 92% aged 3(1/2) to 4, and 99% aged 4 years and over. Binocular linear measures were achieved in 86% of 2- to 3-year-olds and 96% of 3- to 3(1/2)-year-olds who matched or named letters; monocular linear measures were achieved in 86 and 95%, respectively, of these age groups who then accepted occlusion. The median time for completion of the test (binocular and monocular) was 3 minutes 55 seconds. The 95% limits of agreement for the same observer and for different observers were +/-0.13 and -0.19, +0.15 for binocular linear and -0.16, +0.15, and -0.17, +0.13 for monocular linear measures, respectively.

Conclusions: The Sonksen logMAR Test provides reliable binocular and monocular measures of linear visual acuity in a high proportion of children from the age of 2.5 years.