title: Loss of visual acuity is the main reason why reading addition increases after the age of sixty.
abstract: OBJECTIVE
  To determine why the reading addition increases after the age of 55 to 60 years when accommodation is zero.
  
  
  METHODS
  Distance and near visual acuities, arm length, habitual near working distance, reading addition, and pupil diameter were measured in 44 subjects aged >60 years (mean, 72.9 +/- 5.7). Reading addition values were attained using three techniques: least-plus addition using both N-notation text and MN-READ text and the cross-cylinder technique.
  
  
  RESULTS
  The mean dioptric working distance was 2.75 +/- 0.40 D. The reading addition found using N-notation text (+2.21 +/- 0.38 D) was significantly lower than that measured using MN-READ text (+2.48 +/- 0.49 D) or the cross-cylinder method (+2.53 +/- 0.44 D). The reading addition was positively correlated with the dioptric working distance (r = 0.47, p < 0.01), and decreasing habitual working distance was associated with poorer visual acuity (r = -0.42, p < 0.01).
  
  
  CONCLUSIONS
  Our results suggest that decreases in near visual acuity after 60 years of age lead to a reduction in habitual working distance, which increases text angular subtense. In turn, the reduced working distance requires a greater reading addition. Increases in depth of field associated with both suprathreshold text (N-notation) and lower visual acuity lead to reading additions being less than the dioptric working distance.
authors.affiliation: Department of Optometry, University of Bradford, West Yorkshire, United Kingdom.
authors.forename: E S
authors.initials: ES
authors.lastname: MacMillan
authors.forename: D B
authors.initials: DB
authors.lastname: Elliott
authors.forename: B
authors.initials: B
authors.lastname: Patel
authors.forename: M
authors.initials: M
authors.lastname: Cox
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D003867:Depth Perception / Q000502:physiology; D006801:Humans; D008875:Middle Aged; D009790:Occupations; D011305:Presbyopia / Q000503:physiopathology*; D011680:Pupil / Q000502:physiology; D011932:Reading; D014792:Visual Acuity / Q000502:physiology*