Sensitivity and specificity of a visual acuity screening protocol performed with the Lea Symbols 15-line folding distance chart in preschool children.

PURPOSE

The aim of this study was to assess the feasibility of a visual acuity (VA) test using the Lea Symbols 15-line folding distance chart and its diagnostic validity in detecting VA deficiency in preschool children.

METHODS

A group of 149 children aged 38-54 months underwent VA examination performed with the Lea 15-line folding optotype at a distance of 3 metres, according to a test protocol described in the Methods section. After the VA test, a complete ophthalmological examination, including cycloplegic retinoscopy, a cover test and examination of the anterior and posterior segments, was performed on each child in order to detect any VA-threatening ocular abnormality. The Lea Symbols test's sensitivity, specificity, positive and negative likelihood ratios (LR +, LR -) and the receiver operating characteristic (ROC) curve were calculated by means of standard procedures using each VA level of the chart from 0.1 to 1 (1-0 logMAR) as a cut-off point.

RESULTS

The Lea Symbols test could be successfully used in 95.9% of the population. The most useful cut-off points for screening preschool children were found to be 0.8 (LR + 5.73, LR - 0.05) or 0.63 (LR + 11.7, LR - 0.23).

CONCLUSION

The Lea Symbols test proved to be clinically useful in detecting VA deficiency in preschool children. The choice between the two best performing cut-off levels should be made according to the expected cost-effectiveness of the screening programme.