Heart rate variability in normal tension glaucoma: A case–control study

Primary vascular dysregulation (PVD) is believed to be a main cause of local vasospasm and impaired autoregulation as a possible contributing factor in the pathogenesis of normal tension glaucoma (NTG). Subjects with PVD respond stronger to psychological stress. Autonomic dysfunction is another reason of instable ocular blood flow and may be studied by means of assessment of heart rate variability (HRV) especially during a hand-cold provocation test (CPT). To compare the shift of HRV parameters in NTG and healthy subjects after a cold provocation test and to assess the relation between structural damage, circulatory parameters and autonomic dysfunction in NTG. HRV was studied using CPT in 78 NTG patients and 60 health control matches. The ocular blood flow was measured using color Doppler imaging (CDI). The 24 hours blood pressure (BP) monitoring was carried out. The cardiovascular fitness assessment was made to all patients before and after CPT. Mean group difference of HRV parameters was compared between NTG and healthy subjects using the Euclidean metric. The mean ocular perfusion pressure (MOPP) was measured. Optic nerve head and retinal nerve fiber layer (RNFL) were evaluated using spectral-domain optic coherence tomography (SD-OCT). The relation between HRV, CDI, and SD-OCT-parameters was assessed. In contrast to healthy subjects, a predominance of the sympathetic activity after the CPT was revealed in the NTG group. The end diastolic velocity (EDV) in central retinal artery (CRA) and short posterior ciliary artery (SPCA) was significantly reduced in NTG compared to healthy eyes. In NTG, the main HRV parameter characterizing the total effect of autonomic blood circulation regulation (SDNN) correlated with MOPP (0.75, P = .035), SPCA EDV (0.93, P < .001), and CRA EDV (0.9, P < .001). The average daily diastolic BP correlated with RNFL (0.67, P = .009). The NTG patients have the disturbance of the autonomic nervous system, which increases in response to stress provocation and is related to ocular blood flow and structural damage.