title: Effect of retinal image defocus on the thickness of the human choroid.
abstract: OBJECTIVE
  To describe the time-course and amplitude of changes to sub-foveal choroidal thickness (SFCT) induced by imposed hyperopic and myopic retinal defocus and to compare the responses in emmetropic and myopic subjects.
  
  
  METHODS
  Twelve East Asian subjects (age: 18-34 years; six were emmetropic and six had myopia between -2.00 and -5.00 dioptres (D)) viewed a distant target (video movie at 6 m) for 60 min on two separate occasions while optical coherence tomography (OCT) images of the choroid were taken in both eyes every 5 min to monitor SFCT. On each occasion, one eye was optimally corrected for distance with a contact lens while the other eye wore a contact lens imposing either 2.00 D hyperopic or 2.00 D myopic retinal defocus.
  
  
  RESULTS
  Baseline SFCT in myopic eyes (mean ± S.D.): 256 ± 42 μm was significantly less than in emmetropic eyes (423 ± 62 μm; p < 0.01) and was correlated with magnitude of myopia (-39 μm per dioptre of myopia, R(2) = 0.67: p < 0.01). Repeated measures anova (General Linear Model) analysis revealed that in both subject groups, 2.00 D of myopic defocus caused a rapid increase in SFCT in the defocussed eye (significant by 10 min, increasing to approximately 20 μm within 60 min: p < 0.01), with little change in the control eye. In contrast, 2.00 D of hyperopic defocus caused a decrease in SFCT in the experimental eye (significant by 20-35 min. SFCT decreased by approximately 20 μm within 60 min: p < 0.01) with little change in the control eye.
  
  
  CONCLUSIONS
  Small but significant changes in SFCT (5-8%) were caused by retinal defocus. SFCT increased within 10 min of exposure to 2.00 D of monocular myopic defocus, but decreased more slowly in response to 2.00 D of monocular hyperopic defocus. In our relatively small sample we could detect no difference in the magnitude of changes to SFCT caused by defocus in myopic eyes compared to emmetropic eyes.
authors.affiliation: School of Optometry and Vision Science, The University of Auckland, Auckland, New Zealand.
authors.forename: Samuel T-H
authors.initials: ST
authors.lastname: Chiang
authors.affiliation: School of Optometry and Vision Science, The University of Auckland, Auckland, New Zealand.
authors.forename: John R
authors.initials: JR
authors.lastname: Phillips
authors.affiliation: School of Medicine, Deakin University, Geelong, Australia.
authors.forename: Simon
authors.initials: S
authors.lastname: Backhouse
mesh_terms: D000293:Adolescent; D000328:Adult; D044466:Asian People; D002829:Choroid / Q000473:pathology*; D058453:Emmetropia / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000473:pathology* / Q000503:physiopathology; D041623:Tomography, Optical Coherence; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult
keywords: choroid; emmetropia; eye; hyperopia; myopia; optical coherence tomography