A potential association between Alzheimer's disease (AD) and chronic glaucoma has been suggested but results of epidemiological studies have been inconsistent. Therefore, we performed a systematic review and critical appraisal of this literature. We searched systematically in PubMed from December 1964 to September 2013 and identified 239 articles potentially relevant for abstract and full-text review. Statistical heterogeneity (variability) across studies was evaluated using the Cochran Q test and the I (2) statistic, and the Newcastle-Ottawa score was used to assess study quality. Ten studies were finally selected. Compared to non-demented participants, patients with AD had a statistically significant decreased risk of glaucoma but the results were very heterogeneous, and thus summary estimates were not reported (I (2), 89%; P heterogeneity, <0.001). The study results ranged from large positive relative risks identified in small and poorly-conducted studies to weak inverse associations or null estimates observed in some cohort and record-linkage studies, but the summary estimates were essentially driven by a large retrospective cohort using medical claims that may be afflicted by underdiagnosis bias. There was also evidence for substantial publication bias (Egger's P≤0.01). The association of AD and glaucoma is heterogeneous and most studies are small and inadequately designed. Large prospective studies with long follow-ups are warranted to clarify this association.
Keywords: Alzheimer disease; glaucoma; neurodegenerative diseases; systematic review.