This study investigates the relationship between heart rate variability (HRV) and structural damage in patients with normal tension glaucoma (NTG). The primary vascular dysregulation (PVD) is believed to contribute to local vasospasm and impaired autoregulation, leading to NTG. The study compares HRV parameters in NTG patients and healthy controls after a cold provocation test (CPT) and assesses the correlation between HRV, ocular blood flow, and structural damage. **Methods:** - **Participants:** 78 NTG patients and 60 healthy controls. - **Assessments:** HRV using CPT, ocular blood flow with color Doppler imaging (CDI), 24-hour blood pressure (BP) monitoring, and cardiovascular fitness assessment. - **Data Analysis:** HRV parameters were compared between groups using the Euclidean metric. Correlations between HRV, CDI, and structural parameters were analyzed. **Results:** - NTG patients showed a stronger sympathetic response to CPT compared to healthy controls. - Ocular blood flow parameters, such as end-diastolic velocity (EDV) in the central retinal artery (CRA) and short posterior ciliary artery (SPCA), were significantly reduced in NTG. - HRV parameter SDNN correlated with mean ocular perfusion pressure (MOPP), SPCA EDV, and CRA EDV. - Daily diastolic BP correlated with retinal nerve fiber layer (RNFL) thickness. **Conclusion:** - NTG patients exhibit autonomic nervous system dysfunction, particularly sympathetic overactivity, which is associated with ocular blood flow reduction and structural damage. HRV parameters, especially LF and LF/HF, SDNN, HF, and ARI, can be useful additional diagnostic tools for NTG.This study investigates the relationship between heart rate variability (HRV) and structural damage in patients with normal tension glaucoma (NTG). The primary vascular dysregulation (PVD) is believed to contribute to local vasospasm and impaired autoregulation, leading to NTG. The study compares HRV parameters in NTG patients and healthy controls after a cold provocation test (CPT) and assesses the correlation between HRV, ocular blood flow, and structural damage. **Methods:** - **Participants:** 78 NTG patients and 60 healthy controls. - **Assessments:** HRV using CPT, ocular blood flow with color Doppler imaging (CDI), 24-hour blood pressure (BP) monitoring, and cardiovascular fitness assessment. - **Data Analysis:** HRV parameters were compared between groups using the Euclidean metric. Correlations between HRV, CDI, and structural parameters were analyzed. **Results:** - NTG patients showed a stronger sympathetic response to CPT compared to healthy controls. - Ocular blood flow parameters, such as end-diastolic velocity (EDV) in the central retinal artery (CRA) and short posterior ciliary artery (SPCA), were significantly reduced in NTG. - HRV parameter SDNN correlated with mean ocular perfusion pressure (MOPP), SPCA EDV, and CRA EDV. - Daily diastolic BP correlated with retinal nerve fiber layer (RNFL) thickness. **Conclusion:** - NTG patients exhibit autonomic nervous system dysfunction, particularly sympathetic overactivity, which is associated with ocular blood flow reduction and structural damage. HRV parameters, especially LF and LF/HF, SDNN, HF, and ARI, can be useful additional diagnostic tools for NTG.