Background: New, small-target (< 1 degree) random dot stereogram (STRDS) and binocular suppression (STBS) tests appropriate for preschool vision screening were developed to correct the shortcomings of previous such tests, particularly missed cases of anisometropic amblyopia such as found with some RDS-based testing.
Methods: In Experiment 1, the tests were administered to 14 patients with current or a recent history of moderate (< or = 20/60) anisometropic amblyopia, or with accommodative esotropia or monofixation syndrome. All subjects had good binocularity (< or = 100" contour stereoacuity). In Experiment 2, the new tests were administered in a screening setting to a group of 112 three- to five-year-olds to determine testability. Visual acuity, cover testing, and photoscreening were administered as control measures.
Results: In Experiment 1, eleven of the 14 patients failed both tests. Two anisometropic amblyopes passing one or both tests had an acuity < or = 20/30 in the worse eye and < or = 25" stereoacuity. Three anisometropic amblyopia patients failing the STRDS passed another RDS test with similar disparity but a larger target size, confirming a report34 that anisometropic amblyopes may pass RDS testing with parafoveal stereopsis despite the presence of central suppression. The STRDS and STBS tests indicated 80% and 96% specificity, respectively, with the original methodologies; STRDS specificity increased to 95% with retesting with a different methodology. Administration time was 30 sec to 60 sec per test.
Conclusion: Small-target RDS or suppression testing may be more effective for strabismus and amblyopia screening of preschoolers than previous RDS test formats.