title: Axial elongation associated with biomechanical factors during near work.
abstract: OBJECTIVE
  To investigate the changes occurring in the axial length, choroidal thickness, and anterior biometrics of the eye during a 10-minute near task performed in downward gaze.
  
  
  METHODS
  Twenty young adult subjects (10 emmetropes and 10 myopes) participated in this study. To measure ocular biometrics in downward gaze, an optical biometer was inclined on a custom-built height- and tilt-adjustable table. Baseline measures were collected after each subject performed a distance primary gaze control task for 10 minutes to provide washout period for previous visual tasks before each of three different accommodation/gaze conditions. These other three conditions included a near task (2.5 diopters [D]) in primary gaze and a near (2.5 D) and a far (0 D) accommodative task in downward gaze (25 degrees), all for 10 minutes' duration. Immediately after and then 5 and 10 minutes from the commencement of each trial, measurements of ocular biometrics (e.g., anterior biometrics, axial length, choroidal thickness, and retinal thickness) were obtained.
  
  
  RESULTS
  Axial length increased with accommodation and was significantly greater for downward gaze with accommodation (mean ± SD change, 23 ± 13 μm at 10 minutes) compared with primary gaze with accommodation (8 ± 15 μm at 10 minutes) (p < 0.05). A small amount of choroidal thinning was also found during accommodation that was statistically significant in downward gaze (13 ± 14 μm at 10 minutes; p < 0.05). Accommodation in downward gaze also caused greater changes in anterior chamber depth and lens thickness compared with accommodation in primary gaze.
  
  
  CONCLUSIONS
  Axial length, choroidal thickness, and anterior eye biometrics change significantly during accommodation in downward gaze as a function of time. These changes seem to be caused by the combined influence of biomechanical factors (i.e., extraocular muscle forces, ciliary muscle contraction) associated with near tasks in downward gaze.
authors.affiliation: *PhD †PhD, FAAO ‡BSc §BOptom Contact Lens and Visual Optics Laboratory, School of Optometry and Vision Science, Queensland University of Technology, Brisbane, Queensland, Australia (all authors).
authors.forename: Atanu
authors.initials: A
authors.lastname: Ghosh
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Collins
authors.forename: Scott A
authors.initials: SA
authors.lastname: Read
authors.forename: Brett A
authors.initials: BA
authors.lastname: Davis
authors.forename: Payel
authors.initials: P
authors.lastname: Chatterjee
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000869:Anterior Eye Segment / Q000473:pathology; D058452:Axial Length, Eye / Q000473:pathology*; D001696:Biomechanical Phenomena; D001699:Biometry; D002829:Choroid / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000503:physiopathology*; D012160:Retina / Q000473:pathology; D013647:Task Performance and Analysis; D055815:Young Adult