title: Disturbed correlation between arterial resistance and pulsatility in glaucoma patients.
abstract: OBJECTIVE
  (i) To investigate whether pulsatility index (PI) and mean flow velocities (MFV) are altered in glaucoma patients. (ii) To evaluate the significance of PI in retrobulbar autoregulation capacity.
  
  
  METHODS
  Patients with primary open-angle glaucoma (POAG; n = 49), normal tension glaucoma (NTG; n = 62) and healthy controls (n = 48) underwent colour Doppler imaging measurements of the retrobulbar vasculature. Kruskal-Wallis test was used to compare variables between the three diagnostic groups. Restricted cubic splines were used to determine nonlinearities between the resistive index (RI) and PI correlations.
  
  
  RESULTS
  Mean flow velocities (MFV) were lower in both short posterior ciliary arteries (SCPA) and central retinal arteries (CRA) from the two glaucoma groups (p < 0.04 versus healthy controls). No differences were detected in RI or PI in any arteries of the three diagnostic groups (p > 0.08). In healthy individuals, correlations between RI and PI were linear in all arteries. In both POAG and NTG patients, CRA presented a nonlinear curve with a cutpoint at RI 0.77 (p < 0.001) and 0.61 (p = 0.03), respectively, above which the slope increased nearly five- and tenfold (POAG: 1.96 to 10.06; NTG: -0.46-4.06), respectively. A nonlinear correlation in the ophthalmic artery was only observed in NTG patients, with a cutpoint at RI 0.82 (p < 0.001), above which the slope increased from 3.47 to 14.03.
  
  
  CONCLUSIONS
  Glaucoma patients do not present the linear relationships between RI and PI observed in healthy individuals. Their nonlinear relations may be indicative of an altered autoregulation and suggest a possible threshold RI could be determined above which autoregulatory disturbances become more relevant.
authors.affiliation: Department of Ophthalmology, Centro Hospitalar de Lisboa Central, Portugal.
authors.forename: Luís
authors.initials: L
authors.lastname: Abegão Pinto
authors.forename: Evelien
authors.initials: E
authors.lastname: Vandewalle
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Stalmans
mesh_terms: D000368:Aged; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000502:physiology; D019842:Ciliary Arteries / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D005902:Glaucoma, Open-Angle / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006706:Homeostasis; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D057066:Low Tension Glaucoma / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D009880:Ophthalmic Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D011673:Pulsatile Flow; D012039:Regional Blood Flow; D012161:Retinal Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D014065:Tonometry, Ocular; D018615:Ultrasonography, Doppler, Color; D014792:Visual Acuity / Q000502:physiology