Giorgio et al. investigated the structural and functional brain differences between 18 ocular hypertension (OHT) subjects and 29 normal subjects using multi-parametric magnetic resonance imaging (MRI) at 1.5 Tesla. Their findings indicated widespread alterations in the resting-state functional connectivity (FC) of OHT subjects. In contrast, no apparent structural brain change was detected by anatomical MRI or diffusion tensor MRI. At the intra-network level, FC decreased in key cognitive networks. Interestingly, at the inter-network level, FC between default-mode and salience networks decreased, whereas FC between primary and secondary visual networks increased. The decreased FC at both intra- and inter-network levels is in line with previous findings in patients with glaucoma, further suggesting that brain function may be affected early even in the pre-symptomatic stage. On the other hand, the increased FC between primary and secondary visual networks in OHT subjects suggests that adaptive functional reorganization may be taking place.
This pilot study provides an important evidence regarding how the brain is affected under pre-symptomatic conditions. However, several cautions should be noted when interpreting these findings. Firstly, abnormalities observed in this cross-sectional study may not be predictive of a future progression to glaucoma, given that not everyone with OHT will develop glaucoma. To address whether altered FC could serve as an early biomarker for glaucoma, longitudinal observations are necessary in the future.
To address whether altered functional connectivity could serve as an early biomarker for glaucoma, longitudinal observations are necessary
Secondly, the current study did not control for possible confounding effects of risk factors such as ethnicity, diabetes, menopause, family history of glaucoma, etc. Therefore, future studies involving larger population need to take these factors into account. Thirdly, to make the current findings clinically useful, more details should be included and exploited such as the exact intraocular pressure in each eye, how such pressure values were measured, the duration of OHT since diagnosis, etc. Future work may also include behavioral tests and quality-of-life questionnaire to explore the functional implications of the observed FC changes. In summary, this research appears promising, but larger studies will be necessary to confirm the initial results.