title: Optical Coherence Tomography in Alzheimer's Disease: A Meta-Analysis.
abstract: BACKGROUND
  Alzheimer's disease (AD) is a neurodegenerative disorder, which is likely to start as mild cognitive impairment (MCI) several years before the its full-blown clinical manifestation. Optical coherence tomography (OCT) has been used to detect a loss in peripapillary retina nerve fiber layer (RNFL) and a reduction in macular thickness and volume of people affected by MCI or AD. Here, we performed an aggregate meta-analysis combining results from different studies.
  
  
  RESULTS
  Data sources were case-control studies published between January 2001 and August 2014 (identified through PubMed and Google Scholar databases) that examined the RNFL thickness by means of OCT in AD and MCI patients compared with cognitively healthy controls.
  
  
  RESULTS
  11 studies were identified, including 380 patients with AD, 68 with MCI and 293 healthy controls (HC). The studies suggest that the mean RNFL thickness is reduced in MCI (weighted mean differences in μm, WMD = -13.39, 95% CI: -17.34 to -9.45, p = 0.031) and, even more so, in AD (WMD = -15.95, 95% CI: -21.65 to -10.21, p<0.0001) patients compared to HC. RNFL in the 4 quadrants were all significantly thinner in AD superior (superior WMD = -24.0, 95% CI: -34.9 to -13.1, p<0.0001; inferior WMD = -20.8, 95% CI: -32.0 to -9.7, p<0.0001; nasal WMD = -14.7, 95% CI: -23.9 to -5.5, p<0.0001; and temporal WMD = -10.7, 95% CI: -19.9 to -1.4, p<0.0001); the same significant reduction in quadrant RNFL was observed in MCI patients compared with HC (Inferior WMD = -20.22, 95% CI: -30.41 to -10.03, p = 0.0001; nasal WMD = -7.4, 95% CI: -10.08 to -4.7, p = 0.0000; and temporal WMD = -6.88, 95% CI: -12.62 to -1.13, p = 0.01), with the exception of superior quadrant (WMD = -19.45, 95% CI: -40.23 to 1.32, p = 0.06).
  
  
  CONCLUSIONS
  Results from the meta-analysis support the important role of OCT for RNFL analysis in monitoring the progression of AD and in assessing the effectiveness of purported AD treatments.
authors.affiliation: G.B. Bietti Foundation-IRCCS, Department of Neurophysiology of Vision and Neurophthalmology, Rome, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Coppola
authors.affiliation: G.B. Bietti Foundation-IRCCS, Department of Neurophysiology of Vision and Neurophthalmology, Rome, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Di Renzo
authors.affiliation: G.B. Bietti Foundation-IRCCS, Department of Neurophysiology of Vision and Neurophthalmology, Rome, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Ziccardi
authors.affiliation: Istituto Superiore di Sanità, Dipartimento Tecnologie e Salute, Rome, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Martelli
authors.affiliation: Istituto Superiore di Sanità, Dipartimento Tecnologie e Salute, Rome, Italy.
authors.forename: Antonello
authors.initials: A
authors.lastname: Fadda
authors.affiliation: Tor Vergata University of Rome, Department of Clinical Sciences and Translation Medicine; Rome, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Manni
authors.affiliation: IRCCS Istituto Scientifico San Raffaele, Milan, Italy.
authors.forename: Piero
authors.initials: P
authors.lastname: Barboni
authors.affiliation: Sapienza University of Rome Polo Pontino, Department of Medico-Surgical Sciences and Biotechnologies, Latina, Italy; IRCCS-Neuromed, Pozzilli (IS), Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pierelli
authors.affiliation: Doheny Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America.
authors.forename: Alfredo A
authors.initials: AA
authors.lastname: Sadun
authors.affiliation: G.B. Bietti Foundation-IRCCS, Department of Neurophysiology of Vision and Neurophthalmology, Rome, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Parisi
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000175:diagnosis*; D016022:Case-Control Studies; D003710:Demography; D006801:Humans; D017594:Publication Bias; D012160:Retina / Q000473:pathology; D041623:Tomography, Optical Coherence / Q000379:methods*