title: Regional Changes in Choroidal Thickness Associated With Accommodation.
abstract: OBJECTIVE
  To characterize the changes occurring in choroidal thickness (ChT) across the posterior pole during accommodation using enhanced-depth imaging optical coherence tomography (OCT).
  
  
  METHODS
  Forty participants (mean age 21 ± 2 years) had measures of ChT and ocular biometry taken during accommodation to 0, 3, and 6 diopter (D) stimuli, with the Spectralis OCT and Lenstar biometer. A Badal optometer and cold mirror system was mounted on both instruments, allowing measurement collection while subjects viewed an external fixation target at varying accommodative demands.
  
  
  RESULTS
  The choroid exhibited significant thinning during accommodation to the 6 D stimulus in both subfoveal (mean change, -5 ± 7 μm) and parafoveal regions (P < 0.001). The magnitude of these changes varied by parafoveal meridian, with the largest changes seen in the temporal (-9 ± 12 μm) and inferotemporal (-8 ± 8 μm) meridians (P < 0.001). Axial length increased with accommodation (mean change, +5 ± 11 μm at 3 D, +14 ± 13 μm at 6 D), and these changes were weakly negatively associated with the choroidal changes (r2 = 0.114, P < 0.05).
  
  
  CONCLUSIONS
  A small, but significant thinning of the choroid was observed at the 6 D accommodation demand, which was greatest in the temporal and inferotemporal parafoveal choroid, and increased with increasing eccentricity from the fovea. The regional variation in the parafoveal thinning corresponds to the distribution of the nonvascular smooth muscle within the uvea, which may implicate these cells as the potential mechanism by which the choroid thins during accommodation.
authors.forename: Emily C
authors.initials: EC
authors.lastname: Woodman-Pieterse
authors.forename: Scott A
authors.initials: SA
authors.lastname: Read
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Collins
authors.forename: David
authors.initials: D
authors.lastname: Alonso-Caneiro
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D002829:Choroid / Q000473:pathology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D012030:Refractive Errors / Q000473:pathology* / Q000503:physiopathology; D041623:Tomography, Optical Coherence / Q000379:methods*; D055815:Young Adult