title: The influence on unaided vision of age, pupil diameter and sphero-cylindrical refractive error.
abstract: BACKGROUND
  The aim was to derive equations for the relationship between unaided vision and age, pupil diameter, iris colour and sphero-cylindrical refractive error.
  
  
  METHODS
  Data were collected from 663 healthy right eyes of white subjects aged 20 to 70 years. Subjective sphero-cylindrical refractive errors ranged from -6.8 to +9.4 D (mean spherical equivalent), -1.5 to +1.9 D (orthogonal component, J0 ) and -0.8 to 1.0 D (oblique component, J45 ). Cylinder axis orientation was orthogonal in 46 per cent of the eyes and oblique in 18 per cent. Unaided vision (-0.3 to +1.3 logMAR), pupil diameter (2.3 to 7.5 mm) and iris colour (67 per cent light/blue irides) was recorded. The sample included mostly females (60 per cent) and many contact lens wearers (42 per cent) and so the influences of these parameters were also investigated.
  
  
  RESULTS
  Decision tree analysis showed that sex, iris colour, contact lens wear and cylinder axis orientation did not influence the relationship between unaided vision and refractive error. New equations for the dependence of the minimum angle of resolution on age and pupil diameter arose from step backwards multiple linear regressions carried out separately on the myopes (2.91.scalar vector +0.51.pupil diameter -3.14 ) and hyperopes (1.55.scalar vector + 0.06.age - 3.45 ).
  
  
  CONCLUSIONS
  The new equations may be useful in simulators designed for teaching purposes as they accounted for 81 per cent (for myopes) and 53 per cent (for hyperopes) of the variance in measured data. In comparison, previously published equations accounted for not more than 76 per cent (for myopes) and 24 per cent (for hyperopes) of the variance depending on whether they included pupil size. The new equations are, as far as is known to the authors, the first to include age. The age-related decline in accommodation is reflected in the equation for hyperopes.
authors.affiliation: Ophthalmic Research Group, Vision Sciences, Aston University, Birmingham, UK. m.c.m.dunne@aston.ac.uk.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Rushton
authors.affiliation: Ophthalmic Research Group, Vision Sciences, Aston University, Birmingham, UK.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Armstrong
authors.affiliation: Ophthalmic Research Group, Vision Sciences, Aston University, Birmingham, UK.
authors.forename: Mark Cm
authors.initials: MC
authors.lastname: Dunne
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology; D000328:Adult; D000367:Age Factors; D000368:Aged; D003663:Decision Trees; D006801:Humans; D008875:Middle Aged; D011680:Pupil / Q000502:physiology*; D012030:Refractive Errors; D015203:Reproducibility of Results; D014785:Vision, Ocular
keywords: age; ametropia; pupil; vision