title: The Response AC/A Ratio Before and After the Onset of Myopia.
abstract: To investigate the ratio of accommodative convergence per diopter of accommodative response (AC/A ratio) before, during, and after myopia onset.
  
  
  
  Subjects were 698 children aged 6 to 14 years who became myopic and 430 emmetropic children participating in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error. Refractive error was measured using cycloplegic autorefraction, near work by parent survey, and the AC/A ratio by simultaneously monitoring convergence and accommodative response. The response AC/A ratios of children who became myopic were compared with age-, sex-, and ethnicity-matched model estimates for emmetropic children from 5 years before through 5 years after the onset of myopia.
  
  
  
  The response AC/A ratio was not significantly different between the two groups 5 years before onset, then increased monotonically in children who became myopic until reaching a plateau at myopia onset of about 7 Δ/D compared to about 4 Δ/D for children who remained emmetropic (differences between groups significant at P < 0.01 from 4 years before onset through 5 years after onset). A higher AC/A ratio was associated with greater accommodative lag but not with the rate of myopia progression regardless of the level of near work.
  
  
  
  An increasing AC/A ratio is an early sign of becoming myopic, is related to greater accommodative lag, but does not affect the rate of myopia progression. The association with accommodative lag suggests that the AC/A ratio increase is from greater neural effort needed per diopter of accommodation rather than change in the accommodative convergence crosslink gain relationship.
authors.affiliation: The Ohio State University College of Optometry, Columbus, Ohio, United States.
authors.forename: Donald O
authors.initials: DO
authors.lastname: Mutti
authors.affiliation: The Ohio State University College of Optometry, Columbus, Ohio, United States.
authors.forename: G Lynn
authors.initials: GL
authors.lastname: Mitchell
authors.affiliation: The Ohio State University College of Optometry, Columbus, Ohio, United States.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Jones-Jordan
authors.affiliation: Southern California College of Optometry at Marshall B. Ketchum University, Fullerton, California, United States.
authors.forename: Susan A
authors.initials: SA
authors.lastname: Cotter
authors.affiliation: School of Optometry, University of Alabama, Birmingham, Birmingham, Alabama, United States.
authors.forename: Robert N
authors.initials: RN
authors.lastname: Kleinstein
authors.affiliation: University of Houston College of Optometry, Houston, Texas, United States.
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Manny
authors.affiliation: University of Arizona Department of Ophthalmology and Vision Science, Tucson, Arizona, United States.
authors.forename: J Daniel
authors.initials: JD
authors.lastname: Twelker
authors.affiliation: The Ohio State University College of Optometry, Columbus, Ohio, United States.
authors.forename: Karla
authors.initials: K
authors.lastname: Zadnik
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D002648:Child; D003290:Convergence, Ocular / Q000502:physiology*; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D009216:Myopia / Q000175:diagnosis / Q000503:physiopathology*; D012029:Refraction, Ocular / Q000502:physiology*; D012189:Retrospective Studies; D013997:Time Factors