title: Accommodative instability: relationship to progression of early onset myopia.
abstract: BACKGROUND
  In a previous study, we demonstrated that children with early onset myopia had greater instability of accommodation than a group of emmetropic children. Since that study was correlational, we were unable to determine the causal relationship between this and myopic progression. To address this, we examined the children two years later. We predicted that if accommodative instability was causing the myopic progression, instability at Visit 1 should predict the refractive error at Visit 2. Additionally, instability at Visit 1 should predict myopic progression.
  
  
  METHODS
  Thirteen myopic and 16 emmetropic children were included in the analysis. Dynamic measures of accommodation were made using eccentric photorefraction (PowerRefractor) while children viewed targets set at three distances (accommodative demands), namely, 0.25 metres (4.00 D demand), 0.5 metres (2.00 D demand) and 4.00 metres (0.25 D demand).
  
  
  RESULTS
  Both refractive error and accommodative instability at Visit 1 were highly correlated with the same measures at Visit 2. Children with myopia showed greater instability of accommodation (0.38 D) than children with emmetropia (0.26 D) at the 4.00 D target on Visit 1 and this instability of accommodation weakly predicted myopic progression.
  
  
  CONCLUSIONS
  The results presented in the present study suggest that instability of accommodation accompanies myopic progression, although a casual relationship cannot be established.
authors.affiliation: Department of Optometry and Visual Science, Buskerud University College, Kongsberg, Norway. Trine.Langaas@hibu.no
authors.forename: Trine
authors.initials: T
authors.lastname: Langaas
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Riddell
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D017668:Age of Onset; D002648:Child; D018450:Disease Progression; D005139:Eyeglasses; D005500:Follow-Up Studies; D006801:Humans; D009216:Myopia / Q000209:etiology* / Q000503:physiopathology* / Q000628:therapy; D009907:Optometry / Q000379:methods / Q000592:standards; D011237:Predictive Value of Tests; D015203:Reproducibility of Results