Retinal thickness in Alzheimer's disease: A systematic review and meta-analysis

Introduction 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]). Discussion Retinal thickness is decreased in AD and MCI patients compared to HC. This confirms that neurodegenerative diseases may be reflected by retinal changes.