title: Diurnal variation of retinal thickness with spectral domain OCT.
abstract: OBJECTIVE
  To investigate whether diurnal variation occurs in retinal thickness measures derived from spectral domain optical coherence tomography (SD-OCT).
  
  
  METHODS
  Twelve healthy adult subjects had retinal thickness measured with SD-OCT every 2 h over a 10 h period. At each measurement session, three average B-scan images were derived from a series of multiple B-scans (each from a 5 mm horizontal raster scan along the fovea, containing 1500 A-scans/B-scan) and analyzed to determine the thickness of the total retina, as well as the thickness of the outer retinal layers. Average thickness values were calculated at the foveal center, at the 0.5 mm diameter foveal region, and for the temporal parafovea (1.5 mm from foveal center) and nasal parafovea (1.5 mm from foveal center).
  
  
  RESULTS
  Total retinal thickness did not exhibit significant diurnal variation in any of the considered retinal regions (p > 0.05). Evidence of significant diurnal variation was found in the thickness of the outer retinal layers (p < 0.05), with the most prominent changes observed in the photoreceptor layers at the foveal center. The photoreceptor inner and outer segment layer thickness exhibited mean amplitude (peak to trough) of daily change of 7 ± 3 μm at the foveal center. The peak in thickness was typically observed at the third measurement session (mean measurement time, 13:06).
  
  
  CONCLUSIONS
  The total retinal thickness measured with SD-OCT does not exhibit evidence of significant variation over the course of the day. However, small but significant diurnal variation occurs in the thickness of the foveal outer retinal layers.
authors.affiliation: Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia. sa.read@qut.edu.au
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: D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012160:Retina / Q000033:anatomy & histology* / Q000502:physiology*; D041623:Tomography, Optical Coherence / Q000295:instrumentation*; D014792:Visual Acuity