Normal Tension Glaucoma and Cognitive Impairment

Article: Type of glaucoma linked to increased risk of cognitive impairment
Source: British Medical Journal news, via ScienceDaily
Published: March 29, 2021
Article: Glaucoma linked to increased risk of dementia
Source: Flinders University (Australia), via EurekAlert
Published: April 3, 2021

Anterior segment OCT of angle-closure and open-angle glaucoma

Researchers in Australia published a small observational study showing an association between normal-tension glaucoma (NTG) and cognitive impairment. Both normal-tension glaucoma, also known as low-tension glaucoma (LTG), and high-tension glaucoma (HTG) are subtypes of primary open angle glaucoma (POAG), with the difference being the elevation of intraocular pressure or lack thereof. In primary open angle glaucoma, the angle at the trabecular meshwork, an angle formed at the intersection of the cornea and the iris, is open. The other angle-related variation of narrow-angle or angle-closure glaucoma (NAG, ACG) would present with a narrow or closed angle, anatomically obstructing drainage of aqueous humor. Normal-tension glaucoma is more common in people of Asian ancestry while high-tension glaucoma is more common in people of European ancestry. All types of glaucoma display optic nerve damage.

Because the etiology of NTG isn't due to anatomical blockage, excessive aqueous production or inadequate aqueous drainage, its pathology is not fully understood. Furthermore, many cases of glaucoma involve mixed mechanisms. The present investigation into neurological connections with NTG was sparked by links between POAG and dementia in some prior studies. This study involved a health questionnaire of 248 patients with NTG and 349 patients with HTG, all of whom were at least 65 years of age. Among these, 144 patients with NTG and 146 patients with HTG received a cognitive screening; both assessment types were conducted over the phone. The small observational study found that cognitive impairment was twice as prevalent in patients with NTG as it was in those with HTG. The investigators acknowledge a range of limitations with their study. Nonetheless, the study adds information to the body of knowledge about the complexity of glaucoma.

Personal commentary: "High-tension glaucoma" is not a term I have seen used in the U.S., though I have preserved the terminology as it was used in this study from Finland. It is an appropriate term to use in relation to "normal-tension glaucoma." Though "normal-tension glaucoma" and "low-tension glaucoma" are sometimes used synonymously for the kind of glaucoma that is not due to elevated intraocular pressure, the use of "low-tension glaucoma" is more dated and less accurate.

My rating of this study: ⭐

Mullany S, Xiao L, Qassim A, et al. "Normal-tension glaucoma is associated with cognitive impairment." British Journal of Ophthalmology. Published online 29 March 2021. http://doi.org/10.1136/bjophthalmol-2020-317461