title: A test of a linear model of glaucomatous structure-function loss reveals sources of variability in retinal nerve fiber and visual field measurements.
abstract: OBJECTIVE
  Retinal nerve fiber (RNFL) thickness and visual field loss data from patients with glaucoma were analyzed in the context of a model, to better understand individual variation in structure versus function.
  
  
  METHODS
  Optical coherence tomography (OCT) RNFL thickness and standard automated perimetry (SAP) visual field loss were measured in the arcuate regions of one eye of 140 patients with glaucoma and 82 normal control subjects. An estimate of within-individual (measurement) error was obtained by repeat measures made on different days within a short period in 34 patients and 22 control subjects. A linear model, previously shown to describe the general characteristics of the structure-function data, was extended to predict the variability in the data.
  
  
  RESULTS
  For normal control subjects, between-individual error (individual differences) accounted for 87% and 71% of the total variance in OCT and SAP measures, respectively. SAP within-individual error increased and then decreased with increased SAP loss, whereas OCT error remained constant. The linear model with variability (LMV) described much of the variability in the data. However, 12.5% of the patients' points fell outside the 95% boundary. An examination of these points revealed factors that can contribute to the overall variability in the data. These factors include epiretinal membranes, edema, individual variation in field-to-disc mapping, and the location of blood vessels and degree to which they are included by the RNFL algorithm.
  
  
  CONCLUSIONS
  The model and the partitioning of within- versus between-individual variability helped elucidate the factors contributing to the considerable variability in the structure-versus-function data.
authors.affiliation: Department of Psychology, Columbia University, New York, New York 10027, USA. dch3@columbia.edu
authors.forename: Donald C
authors.initials: DC
authors.lastname: Hood
authors.forename: Susan C
authors.initials: SC
authors.lastname: Anderson
authors.forename: Michael
authors.initials: M
authors.lastname: Wall
authors.forename: Ali S
authors.initials: AS
authors.lastname: Raza
authors.forename: Randy H
authors.initials: RH
authors.lastname: Kardon
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D007429:Intraocular Pressure; D016014:Linear Models; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009887:Ophthalmoscopy; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence; D058609:Visual Field Tests; D014794:Visual Fields; D055815:Young Adult