title: Accommodative amplitude required for sustained near work.
abstract: OBJECTIVE
  Many practitioners base the prescription of near vision additions on the assertion that only one half or two-thirds of an individual's amplitude of accommodation is sustainable for a prolonged period. To better understand how much eye focus needs to be restored for presbyopic corrections to be adequate, this study investigated the robustness of the pre-presbyopic human accommodative system during a sustained and intensive near vision task.
  
  
  METHODS
  Twenty-one pre-presbyopic volunteers (aged 26.1 ± 4.7 years) participated in the study. Binocular subjective amplitude of accommodation was measured before and after a prolonged reading exercise, using the RAF rule. During the 30 min reading task, the subject's closest comfortable eye-to-text distance and pupil size was monitored. Accommodative accuracy to 0.2, 1.0, 2.0, 3.0 and 4.0 D stimuli was determined objectively using a validated binocular open-view autorefractor immediately before, and after the reading task.
  
  
  RESULTS
  Amplitude of accommodation (p=0.09) and accommodative accuracy (p>0.05) were statistically unchanged following the intensive near task. The mean proportion of accommodation exerted throughout the near exercise was 80.6% (range 45.3 ± 3.7 to 96.6 ± 4.3%), which increased as the task progressed (F=2.24, p=0.02). The mean percentage of accommodation utilised increased with subject age (r=0.517, p = 0.016).
  
  
  CONCLUSIONS
  The pre-presbyopic human accommodative system is robust to fatigue during intense and prolonged near work. A greater proportion of one's amplitude of accommodation may be continuously exerted than previously suggested.
authors.affiliation: Aston University, School of Life and Health Sciences, Ophthalmic Research Group and Aston Research Centre for Health Ageing, Birmingham, UK. j.s.w.wolffsohn@aston.ac.uk
authors.forename: James S
authors.initials: JS
authors.lastname: Wolffsohn
authors.forename: Amy L
authors.initials: AL
authors.lastname: Sheppard
authors.forename: Sanjay
authors.initials: S
authors.lastname: Vakani
authors.forename: Leon N
authors.initials: LN
authors.lastname: Davies
mesh_terms: D000065:Accommodation, Ocular; D000221:Adaptation, Ocular; D000328:Adult; D000375:Aging; D001248:Asthenopia / Q000503:physiopathology*; D003263:Contact Lenses, Hydrophilic; D003626:Data Display; D005260:Female; D006801:Humans; D008297:Male; D011305:Presbyopia / Q000503:physiopathology*; D011932:Reading; D014792:Visual Acuity; D055815:Young Adult