An evaluation of techniques for measuring stereopsis in infants and young children.

Demonstrating stereopsis is valuable in vision screening of infants and toddlers, since its presence rules out the possibility of profound visual deficits. We assessed the performance of 55 infants and young children on three clinically available tests, the Lang, the Frisby and the TNO. The results were compared with those found using a computerized dynamic random dot stereogram. Most of the children tested were under 3 years of age and 10 were aged under 1 year. The Lang test was passed by 74%, including 50% of those under 1 year. The Frisby test was passed by 65%, but by only 20% of infants under 1 year. Forty-nine per cent passed the TNO test; none were under 1 year. The computerized stereogram was passed by 42.5% of those tested, including 100% of those over 3 years old. Both this test and the TNO presented difficulty in testing infants between 8 months and 2 years because of the increased likelihood that these children would reject the red/green glasses. We recommend that the most appropriate stereotest is largely based on whether the child will tolerate red/green glasses. We would use the dynamic random dot test for infants under 8 months of age, the Lang or Frisby stereotest for infants from 8 months to 30 months, and the TNO or dynamic random dot stereogram after this age.