title: Mean retinal ganglion cell axon diameter varies with location in the human retina.
abstract: OBJECTIVE
  We examined retinal ganglion cell (RGC) axon diameters within the human retinal nerve fibre layer in order to provide information about the possible effects of axonal stimulation when a retinal prosthesis includes the nonfoveal regions.
  
  
  METHODS
  Five pairs of eyes were obtained from donors aged from 48 to 84 years. Fixation delay ranged from 5 to 22 h. Tissue was processed for electron microscopy.
  
  
  RESULTS
  Inferior and/or nasal RGC axons were on average larger than superior and/or temporal axons. The inferior retina contained some very large axons. Foveal axons were on average smaller than nonfoveal axons and had a size distribution that suggested different size groupings not seen in other samples. Peripheral versus central axons within the superior and inferior nasal retinal samples were compared; peripheral axons were significantly larger, unlike the inferior temporal samples or the samples nasal to the optic disc.
  
  
  CONCLUSIONS
  Stimulus-current thresholds will change as a retinal prosthesis increases in size and encroaches on the nonfoveal axons. These changes can be anticipated based on mean axon diameter. Knowing in advance the possible outcome of electrical stimulation of the axonal population may help refine prosthetic procedures and patient training.
authors.affiliation: Department of Clinical Ophthalmology, School of Medical Sciences and Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia. thomas.fitzgibbon@gmail.com
authors.forename: T
authors.initials: T
authors.lastname: FitzGibbon
authors.forename: S F
authors.initials: SF
authors.lastname: Taylor
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000718:Anatomy, Regional; D001369:Axons / Q000648:ultrastructure*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012160:Retina / Q000033:anatomy & histology; D012165:Retinal Ganglion Cells / Q000648:ultrastructure*