Table of contents
Why does the optotype matter?
Why does the optotype matter? Vision screening of very young children requires a test that is sensitive enough to detect problems early, yet simple enough for children to understand. Research shows that many vision tests do not produce comparable results. Some charts are inconsistent, confusing, or inaccurate when used with preschool-aged children, increasing the risk that vision problems go undetected.
The LEA Symbols test system was developed specifically to address these shortcomings. Dr. Lea Hyvärinen designed four familiar shapes, a circle, square, apple, and house, that blur equally at the threshold of vision. Because each symbol blurs at the same rate, the test avoids falsely high acuity scores that occur when children guess from partially visible fragments. This equal-blur principle is a defining feature of the LEA optotype design.
LEA Symbols were calibrated against the traditional Snellen E and later against the standardized Landolt C optotype. As a result, LEA charts are among the few picture-based tests that meet international standards for visual-acuity measurement, a critical requirement for reliable early screening.
Optotype Design and Research Evidence
Clinical accuracy and sensitivity
Clinical research consistently demonstrates the accuracy and reliability of LEA Symbols in preschool vision screening. In a randomized trial comparing the LEA Symbols chart with the Sheridan-Gardiner chart in 260 preschool children, the LEA chart demonstrated a sensitivity of 94.74 percent, while the Sheridan-Gardiner chart showed a sensitivity of only 52.63 percent. High sensitivity is essential in screening, as it ensures that children with genuine vision problems are correctly identified and referred for further evaluation.
The same study reported a higher negative predictive value for LEA Symbols, meaning that children who passed screening were more likely to truly have normal vision. This makes LEA Symbols a preferred tool for preschool screening, where missed cases can have long-term consequences.
Additional laboratory and clinical studies further support the reliability of the LEA optotype. One clinical study found that a 15-line LEA folding chart correctly identified visual acuity in 95.9 percent of 149 preschool children, reinforcing the consistency of LEA Symbols across different screening environments.
LogMAR scaling and international standards
The LEA chart was the first pediatric eye chart designed using a logarithmic, or logMAR, scale. LogMAR scaling improves accuracy compared with traditional Snellen charts because each line represents a constant change in optotype size. This scientific design allows screeners and clinicians to detect smaller differences between the eyes, which is especially important for identifying unilateral vision loss and amblyopia risk.
LogMAR-based charts are endorsed by the World Health Organization for vision screening, reflecting international consensus on best practice. By incorporating logMAR scaling into a child-friendly optotype system, LEA Symbols combine scientific rigor with developmental appropriateness.
Guidelines, standards, and recommended practice
Clinical and public-health guidelines emphasize the importance of validated and standardized optotypes for preschool vision screening. The American Academy of Pediatrics and the American Association for Pediatric Ophthalmology and Strabismus recommend only LEA Symbols or HOTV characters for preschool-aged children.
Other picture charts, including Allen figures, Tumbling E, and Lighthouse characters, are no longer recommended for preschool screening because they are not standardized and may produce inaccurate results. National screening guidelines also specify the use of single-surrounded LEA Symbols or HOTV letters on flipcharts at a 5-foot distance, or full-threshold charts at a 10-foot distance, depending on the screening environment.
A comprehensive pediatric testing system
LEA optotypes are part of a comprehensive pediatric vision assessment system rather than a single acuity chart. The LEA Test System includes distance and near acuity tests, color vision evaluation, low-contrast sensitivity testing, and cognitive vision assessments. Using the same symbols across these tests provides consistency and reduces confusion for young children.
The system also includes stereopsis tests and preferential-looking assessments, enabling evaluation of children who cannot yet respond verbally. These features make LEA tests suitable for screening, clinical assessment, and occupational health evaluations, including use with children who have developmental delays or neurological conditions.
For an overview of how these tools work together within a broader screening framework, see the LEA Vision Test System .
Comparative context and alternative picture tests
Several other pediatric vision tests are available, including the Kay Picture Test, Patti Pics, and charts produced by Oculus. The Kay Picture Test is marketed as a fully researched and validated picture acuity test and uses recognizable images such as a boot, duck, and house. Patti Pics charts promote colorful, engaging symbols calibrated to Sloan standards, while Oculus offers letter, numeral, and picture charts with defined acuity ranges.
These tools may be useful in specific contexts. However, evidence-based guidelines continue to identify LEA Symbols, alongside HOTV letters, as the only picture optotypes recommended for preschool vision screening. When research findings and public-health guidance are considered together, LEA Symbols remain the most consistently endorsed solution.
Conclusion
The design of LEA optotypes, their calibration to internationally recognized standards, and their superior sensitivity in clinical studies establish LEA Symbols as the gold standard for early vision screening. Scientific evidence and authoritative guidelines consistently support their use over other picture-based tests.
When early detection is critical to prevent amblyopia and support healthy visual development, providers and screening programs can rely on LEA tests to deliver accurate, reliable results during the most important years of childhood vision development.
