Preschool screening of visual acuity (VA) is imperative to detect amblyopia and amblyogenic risk factors including refractive error, for early treatment to provide the best visual outcome. However, testability and normative values to determine the most suitable VA test for use at this age needs further investigation as does the effectiveness of VA to detect conditions.
This thesis contains data from two population-based studies of eye health; the Sydney Paediatric Eye Disease Study (SPEDS) (6 months to 6 years) and Sydney Myopia Study (SMS) (6 and 12 years). In SPEDS, comprehensive VA testing was performed using the gold-standard Early Treatment Diabetic Eye Study (ETDRS) logarithmic of Minimum Angle of Resolution (logMAR) chart (including the HOTV matching optotypes), single surrounded Amblyopia Treatment Study (ATS) HOTV Electronic VA test and Teller Acuity Cards II (TAC II). In SMS only the ETDRS was used.
VA testability and normative values improve with age, but variations in VA measures are noted according to the test used. Testability was higher when using the single surround ATS HOTV in comparison to linear HOTV (CSV) logMAR chart. In addition, VA measures with the ATS HOTV were approximately 1 line higher. This indicates that preschool children may not yet have the cognitive maturity to perform a complex linear test to their full VA threshold. In adolescents (SMS), VA was reliable for the detection of significant myopia, but not hyperopia or astigmatism. Finally, the normal distribution of heterophoria was determined to assist in referral criteria for screening programs.
Overall, this thesis has demonstrated that a single surround test such as the ATS HOTV would be suitable for preschool vision screening due to the low false positive values and high testability. Further research must determine an effective and non-invasive screening method to detect significant hyperopia and the age when children reach the cognitive level required to perform linear VA.