Aims The potential association between primary open angle glaucoma (POAG) and Alzheimer's disease (AD) is uncertain and has implications for understanding disease pathogenesis, referral and treatments. The aim was to determine whether individuals diagnosed with POAG are at higher risk of subsequently developing AD or vascular dementia.

Methods A POAG cohort of 87 658 people was constructed from English National Health Service linked hospital episode statistics from 1999 to 2011. An AD cohort (251 703 people), vascular dementia cohort (217 302 people) and reference cohort (>2.5 million people) were constructed in similar ways. Risk of dementia following POAG was determined: rate ratios were calculated based on standardised rates of dementia in the POAG cohort.

Results The risk of AD following a diagnosis of POAG was not elevated: the rate ratio was 1.01 (95% CI 0.96 to 1.06). The risk of vascular dementia after POAG was modestly elevated, with rate ratio 1.10 (1.05 to 1.16). The likelihood of a hospital record of POAG following AD or vascular dementia was very low, with rate ratios 0.28 (0.24 to 0.31) and 0.32 (0.28 to 0.37), respectively.

Conclusions POAG and AD are neurodegenerative conditions that share some pathological features. However, considering AD after POAG, their coexistence at the individual level is no different from that expected by chance. By contrast, a diagnosis of POAG is modestly associated with later development of vascular dementia, presumably owing to shared vascular risk factors. People with dementia in England are much less likely to be admitted subsequently with POAG, perhaps through poor access to hospital eye services and diagnostic challenges.