title: Retinal blood flow in mild cognitive impairment and Alzheimer's disease.
abstract: BACKGROUND
  Patients with Alzheimer's disease (AD) demonstrate the narrowing of retinal veins and decreased retinal venous blood flow compared with control subjects. We assessed whether these abnormalities are present in patients with mild cognitive impairment (MCI).
  
  
  METHODS
  After the determination of the global clinical dementia rating, 52 subjects (10 AD, 21 MCI, and 21 normal controls) underwent retinal hemodynamic profiling. Blood column diameter, blood speed, and blood flow were measured in a major temporal retinal vein using retinal laser Doppler flowmetry. In addition, peripapillary retinal nerve fiber layer (RNFL) thickness was measured using optical coherence tomography.
  
  
  RESULTS
  Blood column diameter in AD was narrower than in both MCI (P = .004) and controls (P = .002). However, blood speed in both AD (P = .024) and MCI (P = .005) was lower than in controls. As a result, the differences in blood flow between AD and MCI (P = .036), AD and controls (P < .0001), and MCI and controls (P = .009) were significant. Although there were no differences in RNFL thickness among the groups, blood flow was correlated (P = .047) with superior RNFL thickness in the AD group, but not in the MCI (P = .40) or control (P = .84) groups.
  
  
  CONCLUSIONS
  Retinal blood flow in MCI is intermediate between what is measured in control subjects and in AD patients. Our findings suggest that blood flow abnormalities may precede the neurodegeneration in AD.
authors.affiliation: Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical, School, Boston, MA, USA.
authors.forename: Gilbert T
authors.initials: GT
authors.lastname: Feke
authors.affiliation: Department of Neurology, Massachusetts Alzheimer's Disease Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Bradley T
authors.initials: BT
authors.lastname: Hyman
authors.affiliation: Department of Neurology, Boston University Alzheimer's Disease Center, Boston University School of Medicine, Boston, MA, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Stern
authors.affiliation: Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical, School, Boston, MA, USA; Department of Medicine, Channing Division of Network Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Louis R
authors.initials: LR
authors.lastname: Pasquale
keywords: Alzheimer's disease; Mild cognitive impairment; Retinal blood flow; Retinal blood speed; Retinal venous blood column diameter