We thank Dr Pai and associates for their helpful insights regarding testability of visual function tests in preschool-aged children.

The Sydney Pediatric Eye Disease Study (SPEDS) corroborates with the testability results from our Strabismus, Amblyopia, and Refractive Error Study (STARS) in many respects, with a few notable small differences. For example, the Singaporean cohort had better logMAR visual acuity (VA) and IOL Master testabilities than the Sydney cohort. In contrast, children in Sydney had better Randot stereoacuity testability than Singaporean children. We agree that these differences can be explained by variability in examiners between the 2 study centers as well as differences in testing protocols and population characteristics. When children in the SPEDS used the electronic visual acuity (EVA) instrument, testabilities were very similar to the STARS logMAR chart. The EVA tester was also utilized in the Multi-Ethnic Pediatric Eye Disease Study (MEPEDS), again leading to similar visual acuity testabilities to that of Singapore, substantiating the Sydney results. Furthermore, the fact that the SPEDS found no differences in testability between Caucasians and East Asians and the MEPEDS found no difference in testability between African Americans and Hispanics supports the lack of a substantial influence of ethnic differences on variability in testability.

There were a few subtle gender differences pointed out by Pai and associates between the Sydney and Singapore studies. Table-mounted autorefraction and Randot stereoacuity were significantly more testable in girls than boys in the STARS, whereas no gender differences were seen for these studies in the SPEDS. These differences are interesting, and highlight possible cultural differences in child development, behavior, and possibly testing conditions, which differentially influence testability of girls versus boys. MEPEDS found gender differences in certain age groups for visual acuity and IOL Master testability, which was not seen in STARS. In all cases, girls outperformed boys. Delineation by age groups of gender differences might demonstrate similar findings in the SPEDS.

Collectively, the 3 studies—STARS, SPEDS, and MEPEDS—provide excellent data from large preschool-aged cohorts on testability of visual function for diverse populations in different countries and cultures. This information provides important insights for the minimum age for testing in future clinical screening programs and community-based research.