title: Longitudinal change and stability of refractive, keratometric, and internal astigmatism in childhood.
abstract: OBJECTIVE
  To assess longitudinal change in refractive, keratometric, and internal astigmatism in a sample of students from a population with a high prevalence of with-the-rule (WTR) astigmatism and to determine the optical origins of changes in refractive astigmatism.
  
  
  METHODS
  A retrospective analysis of longitudinal measurements of right eye refractive and keratometric astigmatism in Tohono O'odham Native American children was conducted. Changes in refractive and keratometric astigmatism per year were compared in a younger cohort (n = 1594, 3 to <11 years old) and an older cohort (n = 648, 11 to <19 years old). Data were analyzed in clinical notation (Cyl) and vector notation (J0, J45).
  
  
  RESULTS
  On average, refractive astigmatism (means: 1.19 diopters [D] Cyl, +0.54 J0, +0.03 J45) resulted primarily from WTR corneal astigmatism (means: +0.85 J0, -0.02 J45) and against-the-rule (ATR) internal astigmatism (means: -0.31 J0, +0.05 J45). Mean longitudinal changes in astigmatism were statistically significant (younger cohort -0.02 D/y Cyl; older cohort +0.06 D/y Cyl). In the younger cohort, astigmatism decreased with age in low and moderate astigmats (<3.00 D) and increased with age in high astigmats (≥3.00 D). In the older cohort, astigmatism increased with age across all levels of astigmatism. Longitudinal changes in keratometric and internal astigmatism were negatively correlated in both cohorts.
  
  
  CONCLUSIONS
  Cross-sectional data suggest the presence of a constant ATR contribution from internal astigmatism (0.60 D Cyl) that is close to the 0.50 D ATR constant reported by Javal and others. Highly astigmatic 3- to <11-year-old children and children older than age 11 years show a small (not clinically significant) increase in astigmatism with age. A negative correlation between changes in keratometric astigmatism and internal astigmatism suggests an active compensation that may contribute to the stability of astigmatism in Tohono O'odham children.
authors.affiliation: Department of Ophthalmology and Vision Science, University of Arizona, Tucson, Arizona, United States College of Public Health, University of Arizona, Tucson, Arizona, United States.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Harvey
authors.affiliation: Department of Ophthalmology and Vision Science, University of Arizona, Tucson, Arizona, United States.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Miller
authors.affiliation: Department of Ophthalmology and Vision Science, University of Arizona, Tucson, Arizona, United States College of Public Health, University of Arizona, Tucson, Arizona, United States.
authors.forename: J Daniel
authors.initials: JD
authors.lastname: Twelker
authors.affiliation: College of Public Health, University of Arizona, Tucson, Arizona, United States.
authors.forename: Duane L
authors.initials: DL
authors.lastname: Sherrill
mesh_terms: D000293:Adolescent; D001130:Arizona / Q000453:epidemiology; D001251:Astigmatism / Q000208:ethnology* / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007198:Indians, North American; D008297:Male; D015995:Prevalence; D012029:Refraction, Ocular / Q000502:physiology*; D012189:Retrospective Studies; D013997:Time Factors
keywords: Native American; astigmatism; children; refractive error development