A new study published in the British Journal of Ophthalmology has established a link between a type of glaucoma and cognitive impairment, a state that commonly precedes dementia. Whilst the study can’t establish causation, it adds to a body of research suggesting that links exist between glaucoma and neurodegenerative illness.
Glaucoma is a condition in which the optic nerve, which transmits all visual information from the retina to the brain, becomes damaged. This is usually due to increased pressure in the eye. One rarer type of glaucoma, called normal-tension glaucoma, involves damage to the optic nerve without any change to normal levels of eye pressure. Untreated glaucoma can lead to visual impairment and even blindness.
Glaucoma and dementia
A previous review had reported an association between a type of glaucoma called primary open-angle glaucoma (POAG) and Alzheimer’s disease. However, the review had also noted that some studies had found no correlation, or in some cases a negative correlation between POAG and Alzheimer’s disease. The new paper, authored by Australian scientists at Flinders University and QIMR Berghofer Medical Research Institute, explored whether this conflicting evidence could be because in some cases, POAG involves higher eye pressure, whereas in others, normal-tension glaucoma is seen.
To look more closely at these subtypes of glaucoma, the researchers examined 144 patients aged 65 years and over from the Australian and New Zealand Registry of Advanced Glaucoma, who were all diagnosed with the normal-tension form of the disease. These individuals were matched by age and sex with 146 high-tension glaucoma patients.
All patients from both groups underwent a health questionnaire and cognitive assessment, which was adapted from a tool used to assess the cognition of blind people, to avoid any confounding from the patients’ impaired vision.
The results were clear. After accounting for a battery of other dementia risk factors,such as smoking, stroke and hypertension, there was a clear increase in cognitive impairment among normal-tension glaucoma patients. The study’s lead author Dr Sean Mullany, an ophthalmologist at Flinders University, summed up the findings: “Cognitive impairment was found to be more than twice as prevalent in patients with normal-tension glaucoma than it was in those with high-tension glaucoma. Our finding of an association between this type of glaucoma and cognitive impairment supports a growing body of evidence suggesting an association between glaucoma and dementia.”
Whilst the study wasn’t able to identify whether cognitive impairment was due to a particular type of dementia and didn’t have any normally sighted controls, it still shines light on a condition that warrants further investigation. Mullany concluded, “This association between normal-tension glaucoma and dementia has the potential to change our understanding about the glaucoma and provides insight into future treatment directions but further research is required to expand on this normal-tension glaucoma–dementia relationship more definitively.”
Reference: Mullany S, Xiao L, Qassim A, et al. Normal-tension glaucoma is associated with cognitive impairment. Br J Ophthalmol. 2021. doi: 10.1136/bjophthalmol-2020-317461