title: Axial growth and changes in lenticular and corneal power during emmetropization in infants.
abstract: OBJECTIVE
  To evaluate the contribution made by the ocular components to the emmetropization of spherical equivalent refractive error in human infants between 3 and 9 months of age.
  
  
  METHODS
  Keratophakometry in two meridians was performed on 222 normal-birthweight infant subjects at 3 and 9 months of age. The spherical equivalent refractive error was measured by cycloplegic retinoscopy (cyclopentolate 1%). Anterior chamber depth, lens thickness, and vitreous chamber depth were measured by A-scan ultrasonography over the closed eyelid.
  
  
  RESULTS
  Both the mean and SD for spherical equivalent refractive error decreased between 3 and 9 months of age (+2.16 +/- 1.30 D at 3 months; +1.36 +/- 1.06 D at 9 months; P < 0.0001, for the change in both mean and SD). Average ocular component change was characterized by increases in axial length, thinning, and flattening of the crystalline lens, increases in lens equivalent refractive index, and decreases in lens and corneal power. Initial refractive error was associated in a nonlinear manner with the change in refractive error (R(2) = 0.41; P < 0.0001) and with axial growth (R(2) = 0.082; P = 0.0005). Reduction in hyperopia correlated significantly with increases in axial length (R(2) = 0.16; P < 0.0001), but not with changes in corneal and lenticular power. Decreases in lenticular and corneal power were associated with axial elongation (R(2) = 0.40, R(2) = 0.12, respectively; both P < 0.0001).
  
  
  CONCLUSIONS
  Modulation in the amount of axial growth in relation to initial refractive error appeared to be the most influential factor in emmetropization of spherical equivalent refractive error. The associations between initial refractive error, subsequent axial growth, and change in refractive error were consistent with a visual basis for emmetropization. The cornea and crystalline lens lost substantial amounts of dioptric power in this phase of growth, but neither appeared to play a significant role in emmetropization.
authors.affiliation: Ohio State University College of Optometry, 338 West Tenth Avenue, Columbus, OH 43210-1240, USA. mutti.2@osu.edu
authors.forename: Donald O
authors.initials: DO
authors.lastname: Mutti
authors.forename: G Lynn
authors.initials: GL
authors.lastname: Mitchell
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Jones
authors.forename: Nina E
authors.initials: NE
authors.lastname: Friedman
authors.forename: Sara L
authors.initials: SL
authors.lastname: Frane
authors.forename: Wendy K
authors.initials: WK
authors.lastname: Lin
authors.forename: Melvin L
authors.initials: ML
authors.lastname: Moeschberger
authors.forename: Karla
authors.initials: K
authors.lastname: Zadnik
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology; D003315:Cornea / Q000502:physiology*; D005123:Eye / Q000254:growth & development*; D005260:Female; D006801:Humans; D007223:Infant; D007908:Lens, Crystalline / Q000502:physiology*; D008297:Male; D009799:Ocular Physiological Phenomena; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000503:physiopathology; D042262:Retinoscopy; D014785:Vision, Ocular / Q000502:physiology*