In the United States, common visual problems in young children include refractive error, strabismus, and amblyopia. Vision impairment related to these conditions can reduce quality of life, function, and school performance. In addition, amblyopia and strabismus can affect normal visual development at a critical period of visual development, resulting in irreversible vision loss. Identification of vision problems prior to school entry could help identify children who might benefit from early interventions to correct or improve vision. The U.S. Preventive Services Task Force (USPSTF) issued an updated recommendation on screening for visual impairment in preschool-aged children in 2004. Since 2004, additional evidence on screening programs and various screening modalities has become available. In 2009, the USPSTF commissioned a new evidence review in order to update its recommendation. The purpose of this report is to systematically evaluate the current evidence on screening for vision problems in preschool-aged children. The most common causes of vision impairment in children are: 1) amblyopia and its associated ("amblyogenic") risk factors, 2) strabismus not associated with amblyopia, and 3) refractive error not associated with amblyopia. Amblyopia is a disorder characterized by abnormal processing of visual images in the brain during a critical period of vision development, resulting in a functional reduction of visual acuity.4 It is associated with conditions that interfere with normal binocular vision, such as strabismus (ocular misalignment), anisometropia (a difference in refractive power between the two eyes), bilateral refractive error, and media opacity (such as cataracts) or other blockage of the visual pathway (such as ptosis or eyelid drooping). Vision impairment associated with amblyopia is not immediately correctable with use of refractive lenses. Standardized definitions for amblyogenic risk factors are available and have been widely adopted. Strabismus is the most common risk factor for amblyopia, but can inhibit development of normal binocular vision even in the absence of amblyopia. Refractive error is commonly due to myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. Unlike vision impairment associated with amblyopia, simple refractive error is correctable with use of appropriate lenses, and is not thought to affect normal visual development. Mild hyperopia is normal in young children, who usually achieve normal (20/20) adult visual acuity between the ages of 3 to 7 years.