llSpectral-Domain OCT Measurements in Alzheimer's Disease: A Systematic Review and Meta-analysis

Topic: OCT is a noninvasive tool to measure specific retinal layers in the eye. The relationship of retinal spectral-domain (SD) OCT measurements with Alzheimer's disease (AD) and mild cognitive impairment (MCI) remains unclear. Hence, we conducted a systematic review and meta-analysis to examine the SD OCT measurements in AD and MCI. Clinical Relevance: Current methods of diagnosing early AD are expensive and invasive. Retinal measurements of SD OCT, which are noninvasive, technically simple, and inexpensive, are potential biomarkers of AD. Methods: We conducted a literature search in PubMed and Excerpta Medica Database to identify studies published before December 31, 2017, that assessed the associations between AD, MCI, and measurements of SD OCT: ganglion cell–inner plexiform layer (GC-IPL), ganglion cell complex (GCC), macular volume, and choroidal thickness, in addition to retinal nerve fiber layer (RNFL) and macular thickness. We used a random-effects model to examine these relationships. We also conducted meta-regression and assessed heterogeneity, publication bias, and study quality. Results: We identified 30 eligible studies, involving 1257 AD patients, 305 MCI patients, and 1460 controls, all of which were cross-sectional studies. In terms of the macular structure, AD patients showed significant differences in GC-IPL thickness (standardized mean difference [SMD], –0.46; 95% confidence interval [CI], –0.80 to –0.11; I2 = 71%), GCC thickness (SMD, –0.84; 95% CI, –1.10 to –0.57; I2 = 0%), macular volume (SMD, –0.58; 95% CI, –1.03 to –0.14; I2 = 80%), and macular thickness of all inner and outer sectors (SMD range, –0.52 to –0.74; all P < 0.001) when compared with controls. Peripapillary RNFL thickness (SMD, –0.67; 95% CI, –0.95 to –0.38; I2 = 89%) and choroidal thickness (SMD range, –0.88 to –1.03; all P < 0.001) also were thinner in AD patients. Conclusions: Our results confirmed the associations between retinal measurements of SD OCT and AD, highlighting the potential usefulness of SD OCT measurements as biomarkers of AD.

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