Recent research suggests a possible association between primary open-angle glaucoma (POAG) and diseases that cause dementia—an umbrella term describing a set of symptoms that includes memory loss, confusion, and impaired executive functions, such as planning, judgment, problem-solving, and emotional control. These studies, however, have yielded mixed results. 

A 2021 study in the British Journal of Ophthalmology sought to clarify this association, particularly the question of whether cognitive impairment is more strongly associated with normal-tension glaucoma (NTG) or high-tension glaucoma (HTG), both of which are subtypes of POAG.* 

What they did

The new study involved a cognitive screening of 290 age- and sex-matched participants made up of 144 NTG patients and 146 HTG controls aged 65 and up who were randomly sampled from the Australian and New Zealand Registry of Advanced Glaucoma (ANZRAG). 

The cognitive screening was performed using the Telephone Version of the Montreal Cognitive Assessment (T-MoCA), which screens cognitive domains, like attention, calculation, language, conceptual thinking, and orientation. The T-MoCA omits questions requiring visual interpretation, minimizing factors related to vision loss in visually impaired participants. 

The research team compared results between the NTG and HTG groups regarding:

• T-MoCA scores
• Demographic data, such as race and sex
• Ocular factors, such as:
  • Internal eye pressure, also known as intraocular pressure (IOP) 
  • Central corneal thickness (CCT) 
  • Visual acuity (how sharply you can discern the details of objects and images)

What they found

The study showed a positive association between NTG and a higher prevalence of impaired cognition compared with HTG, though more comprehensive clinical assessments would be necessary to determine specific dementia-causing diseases. This is one of the largest studies that took possible confounding factors such as a history of stroke, smoking, diabetes, and hypertension into consideration. Hypertension was also found to be associated with cognitive impairment. 

Another strength of this study lies in the fact that visual impairment often results in lower cognition scores when traditional cognitive screening tools are used. This study is the first to account for potentially confounding factors related to vision loss by using a tool developed for the cognitive screening of blind patients. 

The significance and generalizability of the study’s results are limited, however, since:

• The team was unable to follow up with a large percentage of the sample.
• The telephone assessment lends itself to self-reporting bias.
• There was no data about specific dementia-causing diseases patients may have had.
• Socioeconomic status was not taken into consideration.
• No unaffected participants were used in the study as controls. 

What it means

Due to the study’s limitations, no firm conclusions can be drawn regarding the relative prevalence of cognitive impairment in NTG or HTG patients when compared with the general population. Given the strong association between NTG and dementia, however, the study’s authors recommend that clinicians refer older patients with NTG for cognitive assessment.

*Mullany, S., Xiao, L., Qassim, A., Marshall, H., et al. (2021, Feb. 25). Normal-Tension Glaucoma is Associated with Cognitive Impairment. British Journal of Ophthalmology. https://bjo.bmj.com/content/early/2021/02/25/bjophthalmol-2020-317461 

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