title: Influence of Gravity on Ocular Lens Position.
abstract: OBJECTIVE
  We determined whether human ocular lens position is influenced by gravity.
  
  
  METHODS
  Anterior chamber depth (ACD) and lens thickness (LT) were determined with a Haag-Streit Lenstar LS900 for right eyes of participants in two age groups, with a young group of 13 participants aged 18 to 21 years (mean, 21 years; SD, 1 year) and an older group of 10 participants aged 50 to 63 years (mean, 58 years; SD, 4 years). There were two sessions for each participant separated by at least 48 hours, with one session for the usual upright head position and one session for a downwards head position. In a session, testing was done for minimum accommodation followed by testing at maximum accommodation. A drop of 2% pilocarpine nitrate was instilled, and testing was repeated after 30 minutes under minimum and maximum accommodation conditions.
  
  
  RESULTS
  Gravity, manipulated through head posture, affected ACD for young adult and older adult groups but mean effects were only small, ranging from 0.04 to 0.12 mm, and for the older group required the instillation of an accommodation-stimulating drug. Gravity had a weakly significant effect on LT for the young group without accommodation or a drug, but the effect was small at 0.04 ± 0.06 mm (mean ± SD, P = 0.04).
  
  
  CONCLUSIONS
  There is a small but real effect of gravity on crystalline lens position, manifested as reduction in ACD at high levels of accommodative effort with the head in a downwards position. This provides evidence of the ability of zonules to slacken during strong accommodation.
authors.affiliation: Institute of Health and Biomedical Innovation & School of Optometry and Vision Science Queensland University of Technology, Kelvin Grove, Australia.
authors.forename: Lucas J
authors.initials: LJ
authors.lastname: Lister
authors.affiliation: Institute of Health and Biomedical Innovation & School of Optometry and Vision Science Queensland University of Technology, Kelvin Grove, Australia.
authors.forename: Marwan
authors.initials: M
authors.lastname: Suheimat
authors.affiliation: Institute of Health and Biomedical Innovation & School of Optometry and Vision Science Queensland University of Technology, Kelvin Grove, Australia.
authors.forename: Pavan K
authors.initials: PK
authors.lastname: Verkicharla
authors.affiliation: School of Optometry and Vision Science, University of Bradford, Bradford, United Kingdom.
authors.forename: Edward A H
authors.initials: EA
authors.lastname: Mallen
authors.affiliation: Institute of Health and Biomedical Innovation & School of Optometry and Vision Science Queensland University of Technology, Kelvin Grove, Australia.
authors.forename: David A
authors.initials: DA
authors.lastname: Atchison
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000867:Anterior Chamber / Q000033:anatomy & histology; D001699:Biometry; D005260:Female; D006112:Gravitation; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D007908:Lens, Crystalline / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D016684:Prone Position / Q000502:physiology*; D055815:Young Adult