A comparative analysis of Lea Symbols and ETDRS charts in Chinese preschool children's vision examination
Have you ever tried to explain what "blurry vision" feels like to a three-year-old? The challenge of identifying vision problems in young children has puzzled doctors and parents for generations. Imagine trying to assess the eyesight of a preschooler who may not know their letters, feels intimidated by clinical settings, or simply can't articulate what they're seeing. This fundamental challenge in pediatric ophthalmology is what makes the comparison between two vision assessment tools—the playful Lea Symbols chart and the clinical ETDRS chart—so important, especially in the context of Chinese preschool children.
Vision development in early childhood follows a critical period where problems left undetected can lead to permanent visual impairment. The preschool years mark a special window where the visual system remains malleable, and visual deprivation during this time can result in lifelong vision challenges that cannot be fully corrected later in life 3 . With recent surveys in China revealing that visual impairment affects approximately 13.1% of preschool children 3 , the stakes for effective early screening have never been higher.
Assessing vision in young children represents a perfect storm of practical challenges. Unlike adults who can comfortably participate in detailed vision tests, preschoolers may be shy, easily distracted, or unable to verbally articulate what they see. Their attention spans are limited, and traditional eye charts with unfamiliar letters often produce unreliable results due to frustration or lack of engagement.
The cooperation degree of the child becomes just as important as the visual acuity measurement itself. If a child cannot or will not participate in the test, even the most scientifically advanced vision chart becomes useless. This is particularly relevant in China, where large-scale vision screening programs are increasingly implemented to address rising concerns about childhood visual impairment 3 .
Comparison of Lea Symbols (child-friendly symbols) and ETDRS (standard Sloan letters) charts.
The Lea Symbols chart takes a fundamentally different approach to vision assessment. Developed specifically for young children, it features four simple, recognizable shapes: an apple, a house, a circle, and a square. These symbols are designed to be easily identifiable by children as young as two years old, who may not yet know their letters or numbers.
The chart follows the same logMAR (logarithm of the Minimum Angle of Resolution) principles as adult charts, with lines that progress in 0.1 log unit steps and proportional spacing between optotypes. This means that while the symbols are child-friendly, the resulting measurements are scientifically rigorous and comparable to those obtained with traditional charts 2 .
The Early Treatment Diabetic Retinopathy Study (ETDRS) chart represents the "gold standard" for visual acuity assessment in clinical research. Using ten Sloan letters that have been carefully calibrated to be equally recognizable, the chart follows strict design principles with standard progression between lines and proportional spacing 2 .
While unquestionably precise for literate adults and older children, the ETDRS chart faces obvious limitations when used with preschool populations. Young children may not know all the letters, feel intimidated by the unfamiliar shapes, or simply lack the patience to identify multiple similar-looking characters 2 .
In 2019, researchers in China conducted a crucial study directly addressing the question of how these two charts perform with preschool children in a real-world clinical setting 1 . This prospective self-control study enrolled 241 children aged 42 to 78 months from the Quanzhou Quangang Experimental Kindergarten, with a mean age of approximately 5 years.
The research team designed their study with careful attention to scientific rigor. All children received comprehensive ophthalmological examinations first, ensuring that subsequent visual acuity measurements could be properly contextualized. Among the participants, 132 children had normal refractive status, allowing researchers to make particularly valuable comparisons in children without significant vision problems.
Each child underwent monocular visual acuity testing using both the Lea Symbols chart and the ETDRS chart, with all measurements recorded in the standardized logMAR format. This self-controlled approach—where each child served as their own control—eliminated many potential confounding factors and allowed for direct comparison of the two methods within the same individual 1 .
The study followed the principles of the Declaration of Helsinki and received approval from the Medical Ethics Committee of The Second Affiliated Hospital of Fujian Medical University, with written informed consent obtained from all guardians before participation 1 .
In what might surprise many pediatric healthcare providers, both charts achieved remarkably high cooperation rates—96.7% for the Lea Symbols chart and 95.0% for the ETDRS chart. The difference was not statistically significant, suggesting that Chinese preschoolers in this age group (42 months and older) can generally cooperate with either chart 1 .
This finding alone has significant implications for vision screening programs, as it expands the options available to clinicians and screeners. While younger children might still struggle with letter-based charts, the results indicate that from approximately 3.5 years old, most children can participate in formal vision assessment using either system.
Perhaps the most clinically significant finding emerged when researchers compared the actual visual acuity measurements obtained with the two charts. Across the study population, visual acuity measured by the Lea Symbols chart was consistently higher (better) than that measured by the ETDRS chart 1 .
This pattern held true across different age groups and was statistically significant. The consistency of this finding across the population suggests a fundamental difference in how children interact with symbols versus letters, rather than random variation or chart-specific factors.
| Metric | Lea Symbols Chart | ETDRS Chart | Statistical Significance |
|---|---|---|---|
| Cooperation Rate | 96.7% | 95.0% | Not significant (P > 0.05) |
| Visual Acuity in Normal Refractive Children | Higher | Lower | Statistically significant (P < 0.001) |
| Measurement Consistency | Good | Good | Kappa = 0.467 |
| Binocular Vision Difference | No significant difference | No significant difference | Not significant (P = 0.374) |
The study revealed additional nuances that further inform screening practices. Both charts detected that boys consistently showed slightly better visual acuity than girls, a finding that aligns with some previous research in preschool vision development 1 .
Perhaps unsurprisingly, visual acuity values measured by both charts showed negative correlation with age, meaning that older children generally had better (lower) visual acuity scores. This reflects the natural maturation of the visual system throughout early childhood 1 .
Most importantly, the superiority of Lea Symbols measurements over ETDRS measurements held true across all age groups, suggesting that the difference between the charts represents a consistent phenomenon rather than age-specific pattern 1 .
| Age Group | Visual Acuity Pattern | Statistical Significance |
|---|---|---|
| 42-78 months (Overall) | Lea Symbols > ETDRS | P < 0.001 |
| Different age subgroups | Lea Symbols > ETDRS in all groups | P < 0.001 in all cases |
| Age correlation | VA values negatively correlated with age for both charts | P < 0.001 |
The findings from the Chinese preschool study align with international research conducted with other populations. A separate investigation among Tohono O'odham Native American children—a population with a high prevalence of astigmatism—found remarkably similar results 2 .
In that study of 438 children aged 5-7 years, the correlation between Lea Symbols and ETDRS visual acuity was 0.78, indicating a strong but not perfect relationship between the two measures. Critically, the research again found that mean Lea Symbols visual acuity was approximately one-half line better (0.04 to 0.06 logMAR) than mean ETDRS visual acuity, a difference that was statistically significant 2 .
This consistent finding across diverse populations strengthens the conclusion that the measurement differences are inherent to the chart designs and how children process them, rather than cultural or population-specific factors.
What do these findings mean for actual vision screening practices? The consistent superiority of visual acuity measurements with Lea Symbols charts suggests several important considerations for screening programs:
Using ETDRS-based cutoff values for Lea Symbols testing could potentially lead to under-referral of children with actual vision problems. Screening programs need to establish population-specific norms for each chart type rather than applying universal cutoff values 1 .
The high cooperation rates with both charts provide flexibility for screening programs. While Lea Symbols may be preferable for younger children or initial screenings, the ETDRS chart remains a viable option for older preschoolers 1 .
The excellent measurement consistency (Kappa = 0.531) between the two charts means that clinicians can have confidence in results from either method, provided they interpret them with awareness of the systematic differences 1 .
| Consideration | Recommendation | Rationale |
|---|---|---|
| Chart Selection | Lea Symbols preferred for younger children; ETDRS acceptable for older preschoolers | High cooperation rates with both, but symbols more developmentally appropriate |
| Referral Criteria | Establish chart-specific norms and cutoffs | Systematic differences in measured acuity values between charts |
| Interpretation | Always note which chart was used when recording results | Measured values not directly interchangeable between chart types |
| Follow-up | Use same chart type for longitudinal tracking | Consistency improves reliability of monitoring over time |
| Tool/Equipment | Function in Research | Specific Example/Features |
|---|---|---|
| Lea Symbols Chart | Child-friendly visual acuity assessment | Features four recognizable shapes: apple, house, circle, square 2 |
| ETDRS Chart | Gold standard visual acuity measurement | Uses ten Sloan letters with proportional spacing 2 |
| Standardized Illuminator Cabinet | Controls lighting conditions for testing | ESV1500 Illuminated Cabinet provides calibrated photopic (85 cd/m²) and mesopic (3 cd/m²) light levels |
| Visual Acuity Scoring System | Standardized measurement recording | logMAR (logarithm of the Minimum Angle of Resolution) format for precise comparisons 1 |
| Cycloplegic Agents | Temporary paralysis of accommodation for accurate refraction | Cyclopentolate (1%) used in studies to ensure precise refractive measurements 2 |
The comparative analysis of Lea Symbols and ETDRS charts in Chinese preschool children ultimately reveals a powerful truth: when it comes to assessing children's vision, simple shapes often work better than complex letters. The consistent finding that Lea Symbols yield better visual acuity measurements—coupled with equally high cooperation rates—suggests that these child-friendly tools may offer the most developmentally appropriate approach to preschool vision screening.
As China and other nations continue to expand vision screening programs for young children, these findings provide crucial guidance for designing effective, evidence-based protocols. The 13.1% prevalence of visual impairment identified in Chinese preschoolers 3 underscores the vital importance of getting these screening methods right.
Future research may explore whether the consistent measurement differences between chart types reflect fundamental aspects of visual processing in the developing brain or simply the cognitive ease of identifying familiar shapes. What remains clear is that both charts have important roles to play in safeguarding the visual health of our youngest generations—provided we understand their differences and applications.
In the delicate endeavor of protecting children's vision, sometimes the simplest tools—a house, an apple, a circle, a square—prove to be the most sophisticated solutions science can offer.