Diastolic double-product: a new entity to consider in normal-tension glaucoma patients

Vascular insufficiency is considered to play an important role in the pathogenesis of normal-tension glaucoma (NTG). Autoregulation of blood flow in the eye has been shown to be impaired in NTG, resulting in the inability to compensate for changes in intraocular pressure or blood pressure in order to maintain adequate perfusion. To evaluate the occurrence of combined bradycardia-hypotension during 24 hour monitoring of blood pressure and heart rate in patients with NTG. Eleven NTG patients participated in the study. All had episodic symptoms of dizziness or lightheadedness, but were confirmed as not having a diagnosis of orthostatic hypotension. Twenty-four hour monitoring was performed with systemic blood pressure and heart rate automatically measured every 20 minutes during daytime and every hour during the night. The cardiac diastolic and systolic double products (dDP and sDP) at each reading were calculated by multiplying the heart rate by the respective blood pressure. dDP < 3600 and sDP < 5400 (corresponding to a heart rate of 60 beats/min and a blood pressure of 60 and 90 mmHg, respectively) were considered abnormally low, and dDP < 2500 and sDP < 4000 (corresponding to a heart rate 50 beats/min and a blood pressure of 50 and 80 mmHg, respectively) were considered severely abnormal. dDP was abnormally low in all 11 NTG patients on at least one occasion, the majority occurring during the nighttime hours, while abnormally low sDP was present in 8 of the 11 patients. The mean cumulative duration of low dDP readings was 4.2 +/- 3.2 hours. Severely low dDP readings were observed in six patients. Abnormally low dDP was recorded in all NTG patients, lasting more than an hour in the majority of cases. Abnormally decreased dDP may represent a state of cardiovascular autonomic dysregulation, resulting in low ocular perfusion in certain NTG patients.