title: A longitudinal study of accommodative changes in biometry during incipient presbyopia.
abstract: OBJECTIVE
  To profile accommodative biometric changes longitudinally and to determine the influence of age-related ocular structural changes on the accommodative response prior to the onset of presbyopia.
  
  
  METHODS
  Twenty participants (aged 34-41 years) were reviewed at six-monthly intervals over two and a half years. At each visit, ocular biometry was measured with the LenStar biometer (www.Haag-Streit.com) in response to 0.00, 3.00 and 4.50 D stimuli. Accommodative responses were measured by the WAM 5500 Auto Ref/Keratometer (www.grandseiko.com).
  
  
  RESULTS
  During accommodation, anterior chamber depth reduced (F = 29, p < 0.001), whereas crystalline lens thickness (F = 39, p < 0.001) and axial length (F = 5.4, p = 0.009) increased. The accommodative response (F = 5.5, p = 0.001) and the change in anterior chamber depth (F = 3.1, p = 0.039), crystalline lens thickness (F = 3.0, p = 0.042) and axial length (F = 2.5, p = 0.038) in response to the 4.50 D accommodative target reduced after 2.5 years. However, the change in anterior chamber depth (F = 2.2, p = 0.097), crystalline lens thickness (F = 1.7, p = 0.18) and axial length (F = 1.0, p = 0.40) per dioptre of accommodation exerted remained invariant after 2.5 years. The increase in disaccommodated crystalline lens thickness with age was not significantly associated with the reduction in accommodative response (R = 0.32, p = 0.17).
  
  
  CONCLUSIONS
  Despite significant age-related structural changes in disaccommodated biometry, the change in biometry per dioptre of accommodation exerted remained invariant with age. The present study supports the Helmholtz theory of accommodation and suggests an increase in lenticular stiffness is primarily responsible for the onset of presbyopia.
authors.affiliation: Ophthalmic Research Group, Life & Health Sciences, Aston University, Birmingham, UK.
authors.forename: Deborah S
authors.initials: DS
authors.lastname: Laughton
authors.affiliation: Ophthalmic Research Group, Life & Health Sciences, Aston University, Birmingham, UK.
authors.forename: Amy L
authors.initials: AL
authors.lastname: Sheppard
authors.affiliation: Ophthalmic Research Group, Life & Health Sciences, Aston University, Birmingham, UK.
authors.forename: Leon N
authors.initials: LN
authors.lastname: Davies
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D000375:Aging / Q000502:physiology; D000704:Analysis of Variance; D000867:Anterior Chamber / Q000473:pathology; D058452:Axial Length, Eye / Q000473:pathology; D001699:Biometry / Q000379:methods; D005260:Female; D006801:Humans; D007908:Lens, Crystalline / Q000503:physiopathology*; D008137:Longitudinal Studies; D008297:Male; D011305:Presbyopia / Q000503:physiopathology*
keywords: accommodation; biometry; crystalline lens; presbyopia