title: Relationship between retinal nerve fiber layer measurement and signal strength in optical coherence tomography.
abstract: OBJECTIVE
  To examine the relationship between signal strength and retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT).
  
  
  METHODS
  Observational cross-sectional study.
  
  
  METHODS
  Forty normal subjects were recruited.
  
  
  METHODS
  Retinal nerve fiber layer (RNFL) thickness was measured by Stratus OCT (Carl Zeiss Meditec, Dublin, CA). In each eye, the focusing knob was adjusted to obtain 6 images with different signal strengths ranging from 5 to 10. The relationships between signal strength and RNFL thickness were examined using the Spearman correlation coefficient. The differences of RNFL thicknesses were compared with repeated-measures analysis of variance.
  
  
  METHODS
  Retinal nerve fiber layer thicknesses measured at different signal strengths.
  
  
  RESULTS
  Significant differences were observed between measurements obtained at signal strength of 10 and those obtained with signal strength of less than 10 at the superior, nasal, and temporal clock hours. RNFL thickness generally increased with the signal strength, with significant correlations found with the total average, superior, and nasal clock hours RNFL thicknesses.
  
  
  CONCLUSIONS
  Optical coherence tomography RNFL measurements vary significantly with signal strength. Obtaining the maximal possible signal strength is recommended for RNFL thickness measurement.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Chinese University of Hong Kong, Hong Kong, China. carolcheung@cuhk.edu.hk
authors.forename: Carol Yim Lui
authors.initials: CY
authors.lastname: Cheung
authors.forename: Christopher Kai Shun
authors.initials: CK
authors.lastname: Leung
authors.forename: Dusheung
authors.initials: D
authors.lastname: Lin
authors.forename: Chi-Pui
authors.initials: CP
authors.lastname: Pang
authors.forename: Dennis Shun Chiu
authors.initials: DS
authors.lastname: Lam
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D005901:Glaucoma / Q000175:diagnosis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers; D009798:Ocular Hypertension / Q000175:diagnosis; D009898:Optic Disk / Q000033:anatomy & histology*; D009901:Optic Nerve Diseases / Q000175:diagnosis; D012165:Retinal Ganglion Cells / Q000166:cytology*; D041623:Tomography, Optical Coherence / Q000379:methods*; D014794:Visual Fields