title: Retinal ganglion cell count estimates associated with early development of visual field defects in glaucoma.
abstract: OBJECTIVE
  To estimate retinal ganglion cell (RGC) losses associated with the earliest development of visual field defects in glaucoma.
  
  
  METHODS
  Observational cohort study.
  
  
  METHODS
  The study group included 53 eyes of 53 patients with suspected glaucoma who were followed as part of the Diagnostic Innovations in Glaucoma (DIGS) study. These eyes had normal standard automated perimetry (SAP) visual fields at baseline and developed repeatable (3 consecutive) abnormal test results during a median follow-up of 6.7 years. An age-matched control group of 124 eyes of 124 healthy subjects recruited from the general population was included.
  
  
  METHODS
  Estimates of RGC counts were obtained using a previously published model that combines estimates of RGC numbers from SAP sensitivity thresholds and retinal nerve fiber layer (RNFL) thickness measurements with spectral domain optical coherence tomography (SD-OCT). For eyes converting to glaucoma, estimates of RGC counts were obtained at the time (within ± 3 months) of the first abnormal visual field, representing the time of earliest detection of visual field losses.
  
  
  METHODS
  Estimates of RGC counts in eyes converting to glaucoma versus healthy eyes.
  
  
  RESULTS
  The average RGC count estimate in the eyes with early visual field defects was 652057 ± 115829 cells, which was significantly lower than the average of 910 584 ± 142 412 cells found in healthy eyes (P < 0.001). Compared with the average number of RGCs in the healthy group, glaucomatous eyes had an average RGC loss of 28.4%, ranging from 6% to 57%, at the time of the earliest visual field defect on SAP. Retinal ganglion cell counts performed significantly better than the SD-OCT average RNFL thickness parameter in discriminating glaucomatous from healthy eyes with receiver operating characteristic curve areas of 0.95 ± 0.02 versus 0.88 ± 0.03, respectively (P = 0.001).
  
  
  CONCLUSIONS
  Glaucomatous eyes with the earliest detectable visual field loss on automated perimetry may already show substantial loss of RGCs. Empirical estimates of RGC counts combining structural and functional tests agreed closely with previous histologic reports on the number of RGCs associated with early visual fields defects on SAP.
authors.affiliation: Hamilton Glaucoma Center, Department of Ophthalmology, University of California, La Jolla, California 92093-0946, USA. fmedeiros@glaucoma.ucsd.edu
authors.forename: Felipe A
authors.initials: FA
authors.lastname: Medeiros
authors.forename: Renato
authors.initials: R
authors.lastname: Lisboa
authors.forename: Robert N
authors.initials: RN
authors.lastname: Weinreb
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Liebmann
authors.forename: Christopher
authors.initials: C
authors.lastname: Girkin
authors.forename: Linda M
authors.initials: LM
authors.lastname: Zangwill
mesh_terms: D000368:Aged; D002452:Cell Count; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D005901:Glaucoma / Q000150:complications / Q000473:pathology*; D006801:Humans; D008297:Male; D009412:Nerve Fibers / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D011446:Prospective Studies; D012165:Retinal Ganglion Cells / Q000473:pathology*; D013997:Time Factors; D041623:Tomography, Optical Coherence; D058609:Visual Field Tests; D014794:Visual Fields / Q000502:physiology*