title: The time course of blur adaptation in emmetropes and myopes.
abstract: OBJECTIVE
  This study examined the effect of myopic defocus on visual acuity (VA) over time, with attention being paid to the first point at which blur adaptation had a significant and measurable effect on defocused VA. Visual acuity was sampled at a higher rate than previous studies in order to assess the time course of blur adaptation processes in myopic and emmetropic observers.
  
  
  METHODS
  Participants were 24 normally-sighted observers (12 emmetropes and 12 myopes, median age: 22.5 years). All ametropic participants wore their full refractive correction throughout the experiment. 1 D and 3 D of myopic defocus were introduced in two separate, randomised sessions. Visual acuity was measured using Test Chart 2000 at 2 min intervals over a 30 min session whilst looking through defocus lenses. Recovery clear VA was also measured every 2 min for a further 20 min.
  
  
  RESULTS
  Defocused VA was found to improve significantly within 4 min after the introduction of defocus for both 1 D (P < 0.0001) and 3 D conditions (P < 0.0001). The improvements reached a plateau shortly after, with no significant further improvements in defocused VA after 6 min. There were no significant differences found in the temporal blur adaptation profiles between emmetropes and myopes (P = 0.267). Data were fitted with an exponential decay function; the lowest R(2) value for this fit was 0.95.
  
  
  CONCLUSIONS
  Blur adaptation has a clinically significant and measurable effect on VA within 4 min of exposure to defocus. This finding indicates that the visual system instigates the neural compensatory mechanisms shortly after the appearance of defocus. Our results relate particularly to real-life vision of uncorrected myopes or myopes who remove their correction for part of the day.
authors.affiliation: Bradford School of Optometry and Vision Science, University of Bradford, Bradford, UK.
authors.forename: Kiren A
authors.initials: KA
authors.lastname: Khan
authors.forename: Katherine
authors.initials: K
authors.lastname: Dawson
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Mankowska
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Cufflin
authors.forename: Edward A H
authors.initials: EA
authors.lastname: Mallen
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D058453:Emmetropia / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000503:physiopathology*; D013997:Time Factors; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult