title: Variability of the accommodation response in early onset myopia.
abstract: OBJECTIVE
  Hyperopic retinal defocus (blur) is thought to be a cause of myopia. If the retinal image of an object is not clearly focused, the resulting blur is thought to cause the continuing lengthening of the eyeball during development causing a permanent refractive error. Both lag of accommodation, especially for near targets, and greater variability in the accommodative response, have been suggested as causes of increased hyperopic retinal blur. Previous studies of lag of accommodation show variable findings. In comparison, greater variability in the accommodative response has been demonstrated in adults with late onset myopia but has not been tested in children. This study looked at the lag and variability of accommodation in children with early onset myopia.
  
  
  METHODS
  Twenty-one myopic and 18 emmetropic children were tested. Dynamic measures of accommodation and pupil size were made using eccentric photorefraction (PowerRefractor) while children viewed targets set at three different accommodative demands (0.25, 2, and 4 D).
  
  
  RESULTS
  We found no difference in accommodative lag between groups. However, the accommodative response was more variable in the myopes than emmetropes when viewing both the near (4 D) and far (0.25 D) targets. Since pupil size and variability also varied, we analyzed the data to determine whether this could account for the inter-group differences in accommodation variability. Variation in these factors was not found to be sufficient to explain these differences. Changes in the accommodative response variability with target distance were similar to patterns reported previously in adult emmetropes and late onset myopes.
  
  
  CONCLUSIONS
  Children with early onset myopia demonstrate greater accommodative variability than emmetropic children, and have similar patterns of response to adult late onset myopes. This increased variability could result in an increase in retinal blur for both near and far targets. The role of accommodative variability in the etiology of myopia is discussed.
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
authors.forename: Ellen
authors.initials: E
authors.lastname: Svarverud
authors.forename: Ann E
authors.initials: AE
authors.lastname: Ystenaes
authors.forename: Irene
authors.initials: I
authors.lastname: Langeggen
authors.forename: Jan Richard
authors.initials: JR
authors.lastname: Bruenech
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D003623:Dark Adaptation; D018450:Disease Progression; D006801:Humans; D009216:Myopia / Q000503:physiopathology*; D011379:Prognosis; D012029:Refraction, Ocular / Q000502:physiology*; D012160:Retina / Q000503:physiopathology; D012720:Severity of Illness Index; D013997:Time Factors