With recent research suggesting an association between normal-tension glaucoma (NTG) and dementia, authors of a recent study decided to investigate whether cognitive impairment is more strongly associated with NTG than high tension glaucoma (HTG).

This case-controlled study involved 290 age-matched and sex-matched NTG participants (144) and HTG controls (146) ages 65 and younger who were randomly sampled from the Australian and New Zealand Registry of Advanced Glaucoma. Cognitive screening was performed using the Telephone Version of the Montreal Cognitive Assessment, which omits points requiring visual interpretation, accounting for confounding factors related to vision loss in visually impaired participants. Cognitive impairment was defined by a score of <11/22, and cognition was compared between NTG and HTG participants using predetermined thresholds and absolute screening scores.

Results showed no differences in NTG and cohort demographics or ocular parameters at baseline. Cognitive impairment was more prevalent in the NTG group than the HTG group (odds ratio=2.2). Though a linear trend was also observed between lower absolute cognitive scores in the NTG group when compared with the HTG group, it was not statistically significant.

The study concludes that NTG is more strongly associated with cognitive impairment than HTG in older patients with POAG, which supports a glaucoma–dementia association applying to the NTG phenotype.

“Visual impairment has been shown to result in underestimation of cognition in studies using traditional cognitive screening tools. Our study is the first to account for any confounding factors related to vision loss by using a tool developed for cognitive screening in blind patients,” the authors noted in their study. “Moreover, visual impairment is unlikely to have confounded our results, given the similarity in visual acuity between NTG and HTG cohorts at baseline.”

The authors noted there were limitations in this study. “NTG participants in this study demonstrated similar cognitive screening scores to HTG participants, but lower cognitive screening scores than controls,” the authors explained. “No adjustment was made, however, for vision-dependent cognitive tasks that are known to influence cognitive screening scores in visually-impaired patients. Several additional study limitations included small sample sizes of 20 patients per group, exclusion of patients with known dementia and sampling from a younger age range (44-73 years) unlikely to represent the dementia-at-risk age demographics.”

The authors also noted that this NTG-dementia association has the potential to change their understanding of NTG and provide insight into future treatment directions. They add that further research is required to explain this connection more definitively.

Mullany S, Xiao L, Qassim A, et al. Normal-Tension Glaucoma and Cognitive Impairment. Br J Ophthalmol, March 2021. Epub ahead of print.