title: Parameters of accommodative and vergence systems and the development of late-onset myopia.
abstract: OBJECTIVE
  To evaluate whether the characteristics of the oculomotor system are related to the development of late-onset myopia.
  
  
  METHODS
  Forty-four college students were followed for 2 to 3 years. When recruited, 33 of the 44 subjects had emmetropia whereas the remainder (N = 11) had late-onset myopia (LOM). For each subject, dark-focus, dark-vergence, response AC/A, and CA/C ratios, and manifest refraction were measured at 6-month intervals.
  
  
  RESULTS
  The mean dark-focus and AC/A ratios for the subjects (N = 6) who started with emmetropia and became myopic were higher than for the subjects (N = 25) who remained emmetropic. These higher values presented before the refractions exceeded -0.50 D. Interestingly, 7 of 11 subjects with LOM whose myopia increased displayed higher mean AC/A and dark-vergence values and lower mean dark-focus values than the subjects who remained emmetropic.
  
  
  CONCLUSIONS
  The lower dark-focus values found among subjects with LOM seems to be a consequence of the development of myopia. However, myopia might eventually develop in a person with emmetropia with a relatively high AC/A and/or dark-focus values. Therefore, AC/A and dark-focus values may be predictors of the development of myopia.
authors.affiliation: College of Optometry, University of Houston, TX 77204-6052, USA.
authors.forename: B C
authors.initials: BC
authors.lastname: Jiang
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology*; D005500:Follow-Up Studies; D006801:Humans; D009216:Myopia / Q000209:etiology* / Q000503:physiopathology; D009801:Oculomotor Muscles / Q000502:physiology; D010775:Photic Stimulation; D011446:Prospective Studies; D012029:Refraction, Ocular