title: The relationship between visual field index and estimated number of retinal ganglion cells in glaucoma.
abstract: OBJECTIVE
  To evaluate the relationship between visual field index (VFI) and the estimated number of retinal ganglion cells (RGCs) in glaucoma.
  
  
  METHODS
  A multicenter study of 1,245 healthy, glaucomatous and suspected glaucomatous eyes of 1,245 subjects recruited from the Diagnostic Innovations in Glaucoma Study (DIGS) and African Descent and Glaucoma Evaluation Study (ADAGES). All eyes underwent standard automated perimetry (SAP) and time-domain optical coherence tomography (TD-OCT). Estimates of RGC count and percentage of RGCs remaining, compared to age-matched healthy eyes, were calculated from TD-OCT using a previously described formula. Smoothing spline curves were fitted to examine the relationship between VFI and the percent remaining RGCs. The first derivative (i.e., slopes) of these curves was used to explore the relationship between changes in these measures.
  
  
  RESULTS
  The relationships between the VFI and both estimated RGC counts and the percent remaining RGCs were nonlinear. A unit number of VFI loss corresponded to substantially greater loss of estimated RGCs and estimated percentage of RGCs remaining in early compared to late disease.
  
  
  CONCLUSIONS
  The relationship between VFI and estimated RGC counts is nonlinear and the index substantially underestimates the amount of neural loss early in the disease. Disease severity should be taken into account when interpreting rates of VFI change over time.
authors.affiliation: Hamilton Glaucoma Center, Department of Ophthalmology, University of California San Diego, San Diego, California, United States of America ; Boston University School of Medicine, Boston, Massachusetts, United States of America.
authors.forename: Amir H
authors.initials: AH
authors.lastname: Marvasti
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Tatham
authors.forename: Linda M
authors.initials: LM
authors.lastname: Zangwill
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Girkin
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Liebmann
authors.forename: Robert N
authors.initials: RN
authors.lastname: Weinreb
authors.forename: Felipe A
authors.initials: FA
authors.lastname: Medeiros
mesh_terms: D002452:Cell Count; D003710:Demography; D005260:Female; D005901:Glaucoma / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012165:Retinal Ganglion Cells / Q000473:pathology*; D058609:Visual Field Tests; D014794:Visual Fields / Q000502:physiology*