Testability of vision and refraction in preschoolers: the strabismus, amblyopia, and refractive error study in singaporean children. 
To determine the testability of several vision and refraction tests in preschool-aged children.  Population-based study of Chinese preschool-aged children in Singapore.  One thousand five hundred and forty-two Singaporean Chinese children aged 6 to 72 months were recruited through door-to-door screening of government-subsidized apartments in Singapore.  Trained eye professionals administered all tests, including monocular logarithm of the minimum angle of resolution visual acuity with the Sheridan Gardiner chart, monocular Ishihara color testing (Richmond Products Inc, Albuquerque, New Mexico, USA), biometric measurements using IOLMaster (Carl Zeiss, Jena, Germany), and Randot stereoacuity (Stereo Optical Co, Chicago, Illinois, USA) for children 30 to younger than 72 months.  Cycloplegic refraction and keratometry measurements also were determined using a table-mounted autorefractor (Canon Autorefractor RK-F1; Canon, Tokyo, Japan) in children 24 to younger than 72 months.  Testabilities were 84.8% for visual acuity (40.7% for age 30 to < 36 months, 70.8% for age 36 to < 42 months, 86.7% for age 42 to < 48 months, 94.8 for age 48 to < 54 months, 98.6 for age 54 to < 66 months, and 98.7% for age 66 to < 72 months), 81.1% for the Ishihara color test, 82.2% for Randot stereoacuity, 62.2% for table mounted autorefraction, and 91.7% for IOLMaster.  All testabilities significantly increased with age (P < .0001).  Girls had higher testability rates than boys for the autorefraction and Randot stereoacuity tests (P = .036 and .008, respectively).  The vision and refraction tests were testable in a high proportion of preschool-aged Chinese Singaporeans.  Preschool children in older age groups are likely to complete these tests successfully, with important implications for determining age limits for screening in the community and clinic.