title: Blood flow per unit retinal nerve fibre tissue volume is lower in the human inferior retina.
abstract: OBJECTIVE
  To determine if perfusion per unit tissue volume of retinal nerve fibre layer and optic nerve head in the inferior sector is lower than in the superior sector.
  
  
  METHODS
  Heidelberg retinal tomogram (HRT) for topographic measurement of optic nerve head and retinal nerve fibre layer and Heidelberg retinal flowmeter (HRF) for retinal blood flow were performed on 19 normal healthy subjects. Measurements from the superior and inferior sectors were compared. The perfusion/nerve fibre ratio (PNR); the blood flow per unit retinal nerve fibre tissue volume, was calculated in each sector with a formula; HRF flow measurements divided by HRT measurements.
  
  
  RESULTS
  Retinal nerve fibre layer thickness in the inferior retina was significantly higher than in the superior retina (p<0.05). There were, however, no differences in retinal blood flow between the superior and inferior retinal sectors. The PNR in the inferior sector were significantly lower than in the superior sector (p=0.047 for HRF mean flow/rim volume and p = 0.0282 for HRF 75th percentile flow/rim volume).
  
  
  CONCLUSIONS
  The inferior sector of retinal nerve fibre layer and optic nerve head may have lower blood flow per unit nerve tissue volume compared to the superior sector. This result suggests that the inferior sector is more vulnerable to elevated intraocular pressure (IOP) and ischaemic insults in glaucomatous optic neuropathy.
authors.affiliation: Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, USA. alharris@indiana.edu
authors.forename: A
authors.initials: A
authors.lastname: Harris
authors.forename: Y
authors.initials: Y
authors.lastname: Ishii
authors.forename: H S
authors.initials: HS
authors.lastname: Chung
authors.forename: C P
authors.initials: CP
authors.lastname: Jonescu-Cuypers
authors.forename: L J
authors.initials: LJ
authors.lastname: McCranor
authors.forename: L
authors.initials: L
authors.lastname: Kagemann
authors.forename: H J
authors.initials: HJ
authors.lastname: Garzozi
mesh_terms: D000328:Adult; D002196:Capillaries / Q000502:physiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000379:methods; D008297:Male; D008833:Microcirculation / Q000502:physiology; D009412:Nerve Fibers / Q000502:physiology; D009898:Optic Disk / Q000098:blood supply*; D012039:Regional Blood Flow / Q000502:physiology; D012171:Retinal Vessels / Q000502:physiology*; D014054:Tomography / Q000379:methods