Performance of the Lea symbols chart for screening Nigerian children aged 3 to 5 years

Vision screening in children of preschool age (age 3-5 years) gives the opportunity for timely detection of amblyopia. The tools that would be used for screening must have high rates of testability in these young children, and must have high enough sensitivity and specificity to be reliable and cost effective.

To assess the performance of the Lea symbols chart as a screening tool in children aged 3 to 5 years attending primary schools in Kwara State, Nigeria.

Visual acuity (VA) of 464 children selected from 12 schools by a multistage sampling procedure was checked using the Lea symbols chart by trained Lea screeners. Children meeting the referral criteria and untestable children had a comprehensive eye examination. Testability rates, sensitivity, specificity, positive, and negative predictive values were analyzed based on age and gender, with corresponding significance values generated.

Testability rates among 5 year olds were as high as 99.1%, decreasing significantly to 95.5% in 4 year olds and 85.7% in 3 year olds (p value < 0.001). Visual acuity performance improved with age (p value 0.002) but was unrelated to gender. The Lea symbols chart had an overall specificity of 77.4% (63.2% among 3 year olds and 83.5% among 5 year olds). At VA thresholds of 6/12 for 5 year olds and 6/15 for 3-4 year olds, the screening tool became 87.7% specific among 3 year olds and 94.3% specific among 5 year olds (overall 92.5%).

The Lea symbols chart was found to be a useful screening tool in this environment, especially among 5 year olds. The reduced specificity among 3-4 year olds may prompt further research into the appropriate VA thresholds for 3-4 year olds to reduce the burden of unnecessary comprehensive eye evaluations resulting from too many false positive results.