Corneal astigmatism in preschool Native Americans.

BACKGROUND: Native Americans tend to have high amounts of corneal and refractive with-the-rule astigmatism. This condition is reported to be of recent onset. Astigmatism has been shown to be prevalent in preschool-age children but, because of the process of emmetropization, this condition generally disappears by school age. Navajo children have been shown, however, to enter first grade with high mean amounts and high prevalence of with-the-rule astigmatism. This study was undertaken to ascertain whether with-the-rule astigmatism decreased in Navajo preschool children as they grew older. METHODS: Cross-sectional keratometric data were gathered on 250 preschool Navajo children from three states in the four corners district of the Navajo nation. RESULTS: High mean amounts of with-the-rule corneal astigmatism are prevalent at each age represented in this study. Girls have steeper corneas and more astigmatism than boys. Although the steepness of the corneal curve generally decreases slightly but significantly with age, the calculated astigmatism does not. The steepness of corneas also appears to vary by geographical area of residence within the Navajo nation. CONCLUSIONS: Emmetropization, with respect to the disappearance of astigmatism, does not appear to take place among the Navajo as it does in either Caucasian or Asian preschool-age children.