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Development of Crowding Distance in Children Is Faster and Later Than Visual Acuity and Better Predicts Reading
Sarah J Waugh1,2, Monika A Formankiewicz3, Leticia Álvaro4
1Centre for Vision across the Life Span, School of Applied Sciences, University of Huddersfield, West Yorkshire, United Kingdom.
Investigative Ophthalmology & Visual Science
|May 6, 2026
Summary
Visual crowding, not visual acuity, significantly impacts children's reading performance. Crowding distance develops later than acuity and may help identify reading difficulties.
Area of Science:
- Developmental ophthalmology
- Pediatric vision science
- Reading acquisition
Background:
- Visual crowding hinders object recognition in cluttered environments.
- Crowding distance (CD) is the minimum spacing for target identification, while visual acuity (VA) measures the smallest recognizable letter size.
- Understanding the developmental trajectories of CD and VA is crucial for assessing reading development in children.
Purpose of the Study:
- To investigate the developmental changes in visual crowding distance (CD) and visual acuity (VA) in children aged 3-11 years.
- To determine the relationship between CD, VA, and teacher-assessed reading performance.
- To compare the impact of CD and VA on reading indicators.
Main Methods:
- Measured visual acuity (VA) and crowding distance (CD) in 227 children (3-11 years) and 40 adults.
- CD was assessed using trigram and repeated optotype arrangements.
- Converted teacher-assessed reading indicators into a study reading indicator (SRI) for 200 children.
Main Results:
- VA reached near-adult levels by age six, while CD matured later, by age eight.
- Crowding distance (CD) showed a stronger correlation with reading performance (SRI) than visual acuity (VA).
- After accounting for age, CD remained a significant predictor of reading performance, whereas VA did not.
Conclusions:
- Visual crowding develops more slowly and matures later than visual acuity in children.
- Crowding distance is a more significant factor in children's reading performance than visual acuity.
- CD measures may offer a more sensitive diagnostic tool for visual processing issues affecting reading.
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