Vision screening of preschool children detects problems that can cause irreversible loss. The most targeted condition in this population is amblyopia (lazy eye) occurring in approximately two to five percent of the population. This collaborative public health study of preschool vision screening compares screening tests in two socio-economically distinct populations. Methods: Preschool children, aged two to six years, will be recruited from: 1) the NSU affiliated preschool programs and 2) Caridad Health Clinic serving indigent children of Mexican farm workers. Each child will be screened with two visual acuity tests and two stereoacuity tests. Each test attempt will be timed. Children who do not complete the initial testing attempt will be retested. If a child does not complete the test on the second attempt, he or she will be classified as failing that test. To pass the vision screening, the child must pass one visual acuity test and the stereoacuity test. Each child who fails the screening will be referred for a complete eye examination. In addition, a control group, every fourth child who passed the screening, will be referred for an eye examination. Neither the parents, nor the children, nor the clinical examiner who performs the eye examination will know whether the child passed or failed the screening prior to the eye examination. Data Analysis: Data collected will be used to calculate the testability, sensitivity, and specificity of each test. Results will be analyzed for differences by age and population using analysis of variance (ANOVA) with post-hoc LSD tests. Significance: This study will yield 1) benefits for the communities that it serves and 2) scientific contributions in vision science. The study is double-blind and is unique, in that eye examinations are also offered to children who pass the screening to measure the effectiveness of the instruments under investigation.