Ocular diagnostics and occipital neurovascular coupling in ocular hypertension and open angle glaucoma

Introduction: The relationship between glaucoma and neurovascular coupling in the visual cortex has yet to be fully explored and understood. This study employs the time-domain (TD) functional near-infrared spectroscopy (fNIRS) technique to noninvasively monitor the hemodynamic response function (HRF) in the visual cortex. Methods: 203 eyes (104 subjects, 46 females, 58 males): 44 with ocular hypertension (OHT), 38 with open-angle glaucoma (OAG), 54 with normal tension glaucoma (NTG), and 67 without abnormal/pathologic condition, were analyzed. All subjects had a complete eye examination, including Goldmann tonometry, computerized visual field optical coherence tomography, pattern electroretinogram, and visual evoked potentials. Visual cortex HRF was assessed by TD-fNIRS using a standard stimulation protocol (reversed checkerboard at 10 Hz). Multivariate statistical analysis was performed to obtain groups (clusters) of eyes based on the respective TD- fNIRS parameters. The relationships between the clusters and the diagnostic groups were assessed by comparing the distributions of the former ones among healthy, hypertensive and glaucomatous eyes. Results: We found six clusters of eyes, five representing eyes with consistent measurements of HRF amplitudes across acquisition channels (left/right hemisphere) and repeated stimuli, distinguished by distinct magnitudes of neurovascular coupling. The sixth cluster included all the cases of incoherent HRF patterns. Evidence of a different distribution between glaucomatous and healthy eyes was found (p = 0.0009), suggesting that high levels of neurovascular coupling are less likely to be observed in NTG and OAG groups. Conclusion: Occipital TD-fNIRS could be fruitfully implemented in a clinical setting to provide significant and easy-to-get insights on neurovascular dynamics, supporting the differential diagnosis of glaucomatous patients. Our findings highlight the importance of the underappreciated correlates between glaucoma and overall neurologic status.