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The pattern of astigmatism in a Canadian preschool population
Laura Cowen1, William R Bobier
1Department of Statistics and Actuarial Sciences, University of Waterloo, Waterloo, Ontario, Canada.
Insights
Astigmatism in Canadian preschoolers is common, with most cases being with-the-rule (WTR). Over 1.25 D of astigmatism exceeds the 95th percentile for this age group.
Area of Science:
- Ophthalmology
- Pediatric Optometry
- Public Health
Background:
- Astigmatism is a common refractive error affecting visual acuity.
- Understanding astigmatism prevalence in preschool children is crucial for early intervention.
- Previous studies on preschool astigmatism have varied methodologies and populations.
Purpose of the Study:
- To determine the magnitude, type, and central tendency of astigmatism in a Canadian preschool population.
- To establish normative data for astigmatism in young children.
- To compare autorefraction and retinoscopy findings in this age group.
Main Methods:
- Noncycloplegic autorefraction was performed on 1179 preschool children.
- Spherocylinder measures were mathematically transformed into independent components.
- Data were analyzed to determine astigmatism prevalence and types.
Main Results:
- With-the-rule (WTR) astigmatism was the most frequent type (45%), followed by against-the-rule (ATR; 40%).
- The 95th percentile for cylinder magnitude was 1.25 D; higher values were predominantly WTR.
- The mean cylinder magnitude was low (0.08 D), with central tendency near zero when analyzed continuously.
Conclusions:
- The central tendency of astigmatism in preschool children is close to zero when analyzed mathematically.
- Astigmatism exceeding 1.25 D is rare, representing the 95th percentile in this population.
- WTR astigmatism is the predominant type among preschool children with significant astigmatism.
Purpose:
To measure magnitude, type, and central tendency of astigmatism found in a county-wide population of Canadian preschool children (mean age, 48.1 months).
Methods:
Noncycloplegic autorefractive measures were taken in 1179 children attending a preschool health fair operated by their county board of health. Spherocylinder measures were transformed into three independent components.
Results:
The equivalent sphere showed considerable variation between retinoscopy and autorefraction that was attributed to the variable overaccommodation induced by the autorefractor. Astigmatic components were not affected. Small discrepancies between the two techniques were similar to those in adults and were not of sufficient magnitude to affect validity. With-the-rule (WTR) astigmatism of at least 0.25 D was the most frequent form (45%) followed by against-the-rule (ATR; 40%) and oblique (15%). The 95th percentile for cylinder magnitude was found at 1.25 D. Astigmatisms beyond this value were predominately WTR. The mean (negative) cylinder magnitude was 0.08 Dx 015 degrees.
Conclusions:
When spherocylinder values are transformed into a mathematical continuum rather than WTR and ATR classifications, the true central tendency of the population is better defined and is close to zero. Astigmatisms of more than 1.25 D in the preschool child exceed the 95th percentile in this population and were more frequently WTR.
