The stability of astigmatism in native American preschool children

Introduction: Some Native American tribes, including the Tohono O'Odham, have been noted to have high amounts of refractive astigmatism. We report the change of astigmatism over a period of at least a year in a group of Head Start preschool children. Methods: Subjects were 179 children whose parents provided informed consent. Children averaged 3.6 years age at enrollment. Most were seen 3 (n=51) or 4 times (n=124) over two years of participation, with 4 children seen 5 or 6 times. Cycloplegic autorefraction (Nikon Retinomax K-Plus), confirmed by retinoscopy, was performed. A Mixed-Model (random effects) analysis of astigmatism change over time was performed using Stata XTREG. Results: Astigmatism was remarkably stable. For the entire group of subjects, a modest gain (p=0.000) of astigmatism of 0.066 Diopters / year (D/yr), (95% CI 0.032 - 0.099 D/yr) was noted. When stratified by the within-child average astigmatism magnitude, children with no-to-low astigmatism, averaging less than 1.5 D (n=123) had increase of astigmatism estimated at 0.035 D/yr, with 95% CI of .00107 to .0693 D/yr (p=0.043). Children with moderate average astigmatism (1.5 - <3 D) (n=36) showed a larger increase in astigmatism per year (0.099 D/yr., 95% CI 0.0131 to 0.184 D/yr) (p=0.024). Those children who had the most astigmatism (averaging >= 3 D) (n=20) over the longitudinal observation had the largest increase in astigmatism per year, estimated to be 0.173 D/yr, with 95% confidence interval of 0.0471 to 0.300 D/yr (p=0.007). Conclusion: In these children, loss of astigmatism over time was not observed. In fact, a minimal but statistically significant increase in measured astigmatism was observed over the measurement period. It does not appear that these children emmetropize the astigmatic component of their refractive error during the preschool years.