Using the KM visual acuity chart for more reliable evaluation of amblyopia compared to the HVOT method

Purpose: To evaluate a new letter matching visual acuity (VA) chart (the KM chart) for children aged 5-7 years, designed as a Monoyer-based chart, in order to obtain a better consistency between school and preschool VA recordings. Methods: Visual acuities were assessed using three methods: the HVOT, KM and Monoyer charts. Comparisons were made between the KM method versus the HVOT and Monoyer methods, respectively. Children with normal vision and with different degrees of amblyopia were investigated. Results: Visual acuity levels appeared significantly higher in children with amblyopia when tested with the HVOT chart than when tested with the KM chart. Visual acuities obtained with the Monoyer and KM methods were comparable. The difference between the Monoyer and KM methods on the one hand, and the HVOT method on the other, can be explained by the fact that the HVOT chart elicits less crowding effect than the other two charts. Conclusions: Visual acuity in children with amblyopia might be overestimated if the HVOT test alone is used to assess vision. Use of the HVOT chart, therefore, should be restricted to the 3.5-4.5 years age group, for whom the KM chart is somewhat too difficult. In our opinion the KM chart should be preferred for use with older preschool children because it shows good consistency with the Monoyer chart.