title: Retinal thickness in Alzheimer's disease: A systematic review and meta-analysis.
abstract: BACKGROUND
  Retinal characteristics are increasingly recognized as biomarkers for neurodegenerative diseases. Retinal thickness measured by optical coherence tomography may reflect the presence of Alzheimer's disease (AD). We performed a meta-analysis on retinal thickness in AD and mild cognitive impairment (MCI) patients and healthy controls (HCs).
  
  
  METHODS
  We selected 25 studies with measurements of retinal thickness including 887 AD patients, 216 MCI patients, and 864 HCs that measured retinal thickness. Outcomes were peripapillary retinal nerve fiber layer (RNFL) and macular thickness. The main outcome was the standardized mean differences (SMDs). We used STATA to perform the meta-analysis (StataCorp, Texas; version 14.0).
  
  
  RESULTS
  Relative to HCs, AD and MCI patients had lower peripapillary RNFL (SMD 0.98 [CI -1.30, -0.66,P< .0001] and SMD 0.71 [CI -1.24, -0.19,P= .008]). Total macular thickness was decreased in AD patients (SMD 0.88 [CI -1.12, -0.65,P= .000]).
  
  
  CONCLUSIONS
  Retinal thickness is decreased in AD and MCI patients compared to HC. This confirms that neurodegenerative diseases may be reflected by retinal changes.
authors.affiliation: Neurology, VU University Medical Center Alzheimer Center, Amsterdam, The Netherlands.
authors.forename: Jurre
authors.initials: J
authors.lastname: den Haan
authors.affiliation: Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; Ophthalmology Department, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Frank D
authors.initials: FD
authors.lastname: Verbraak
authors.affiliation: Neurology, VU University Medical Center Alzheimer Center, Amsterdam, The Netherlands; Alzheimer Centre, School for Mental Health and Neuroscience (MHeNS), University Medical Centre, Maastricht, The Netherlands.
authors.forename: Pieter Jelle
authors.initials: PJ
authors.lastname: Visser
authors.affiliation: Neurology, VU University Medical Center Alzheimer Center, Amsterdam, The Netherlands.
authors.forename: Femke H
authors.initials: FH
authors.lastname: Bouwman
keywords: Alzheimer's disease (AD); Biomarkers; Eye; Meta-analysis; Mild cognitive impairment (MCI); Optical coherence tomography (OCT); Retinal thickness