Many school systems have regular vision screening programs that are carried out by volunteer professionals, school nurses, and/or properly trained laypersons. Screening can be done quickly, accurately, and with minimum expense by one of these individuals. The screener should not have a vested interest in the screening outcome. As with all screening programs, vision screening should be performed in a fashion that maximizes the rate of problem detection while minimizing unnecessary referrals and cost. Beginning in the preschool years, those conditions which can be detected by a vision screening using an acuity chart are reduced vision in one or both eyes from amblyopia, uncorrected refractive errors or other eye defects and, in most cases, misalignment of the eyes (called strabismus).