title: Retinal nerve fiber layer measurements by scanning laser polarimetry with enhanced corneal compensation in healthy subjects.
abstract: OBJECTIVE
  To evaluate the (i) effects of biological (age and axial length) and instrument-related [typical scan score (TSS) and corneal birefringence] parameters on the retinal nerve fiber layer (RNFL) measurements and (ii) repeatability of RNFL measurements with the enhanced corneal compensation (ECC) protocol of scanning laser polarimetry (SLP) in healthy subjects.
  
  
  METHODS
  In a cross-sectional study, 140 eyes of 73 healthy subjects underwent RNFL imaging with the ECC protocol of SLP. Linear mixed modeling methods were used to evaluate the effects of age, axial length, TSS, and corneal birefringence on RNFL measurements. One randomly selected eye of 48 subjects from the cohort underwent 3 serial scans during the same session to determine the repeatability.
  
  
  RESULTS
  Age significantly influenced all RNFL measurements. RNFL measurements decreased by 1 µm for every decade increase in age. TSS affected the overall average RNFL measurement (β=-0.62, P=0.003), whereas residual anterior segment retardance affected the superior quadrant measurement (β=1.14, P=0.01). Axial length and corneal birefringence measurements did not influence RNFL measurements. Repeatability, as assessed by the coefficient of variation, ranged between 1.7% for the overall average RNFL measurement and 11.4% for th nerve fiber indicator.
  
  
  CONCLUSIONS
  Age significantly affected all RNFL measurements with the ECC protocol of SLP, whereas TSS and residual anterior segment retardance affected the overall average and the superior average RNFL measurements, respectively. Axial length and corneal birefringence measurements did not influence any RNFL measurements. RNFL measurements had good intrasession repeatability. These results are important while evaluating the change in structural measurements over time in glaucoma patients.
authors: *VST Glaucoma Center †Center for Clinical Epidemiology and Biostatistics, L V Prasad Eye Institute, Banjara Hills, Hyderabad, Andhra Pradesh, India.
authors: Harsha L
authors: HL
authors: Rao
authors: Chirravuri R
authors: CR
authors: Venkatesh
authors: Kelli
authors: K
authors: Vidyasagar
authors: Ravi K
authors: RK
authors: Yadav
authors: Uday K
authors: UK
authors: Addepalli
authors: Aarthi
authors: A
authors: Jude
authors: Sirisha
authors: S
authors: Senthil
authors: Chandra S
authors: CS
authors: Garudadri
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D058452:Axial Length, Eye / Q000033:anatomy & histology; D001718:Birefringence; D003315:Cornea / Q000502:physiology; D003430:Cross-Sectional Studies; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers; D009898:Optic Disk / Q000033:anatomy & histology*; D012165:Retinal Ganglion Cells / Q000166:cytology*; D057109:Scanning Laser Polarimetry; D014794:Visual Fields; D055815:Young Adult