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Editors Selection IGR 13-2

Forms of Glaucoma: Normal Tension Glaucoma

Comment by Alon Harris on:

78478 Blood Pressure and Heart Rate Variability in Primary Open-Angle Glaucoma and Normal Tension Glaucoma, Lindemann F; Kuerten D; Koch E et al., Current Eye Research, 2018; 43: 1507-1513

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The reduction of intraocular pressure (IOP) remains the only currently proven and approved method to arrest the onset and progression of glaucoma. However, the complex and multifactorial nature of the disease allows for many individuals to suffer glaucomatous vision loss despite low initial IOP and/or significantly reduced IOP via medical intervention. Vascular contributions to the disease process are fairly well established with ocular perfusion pressure (defined as 2/3 mean arterial pressure - IOP) being recognized as an independent risk factor for the disease.¹ Determining individual risk often involves careful consideration of IOP, age, race, gender, and other cofounders such as systemic vascular health.

These physiological parameters significantly vary over a 24-hour period with postural and diurnal variation unaccounted for in the current study

Lindemann and colleagues present novel data on blood pressure (BP) and heart rate variability patterns in 37 patients with (high pressure) primary open-angle glaucoma (POAG), 27 patients with normal-tension glaucoma (NTG), and 87 control subjects. Under resting conditions, continuous BP and heart rate were simultaneously recorded over 30 min with time series of heart rate, systolic blood pressure and diastolic blood pressure analyzed utilizing univariate linear (time domain, frequency domain), non-linear (symbolic dynamics), and bivariate (joint symbolic dynamics) indices. The authors identified 12 significantly different parameters between POAG patients and controls, however they found a full 80 parameters that were significantly different between NTG patients and controls. The data showed a much higher sensitivity (82% at a specificity of 87%) for NTG patients compared to high pressure POAG suggesting impaired patterns of autonomic cardiovascular regulation in glaucoma, especially within NTG patients.

The use of continuous monitoring (30 min) to examine systemic differences in vascular health is unique and a strength of the current study as is the inclusion of both high and low pressure glaucoma patients to elicit differences in risk profiles. Conversely, a limitation is the absence of a direct ocular blood flow modality such as optical coherence angiography, which may have shown how these systemic vascular disturbances influence perfusion to the retina and optic nerve head. It is also important to acknowledge that these physiological parameters significantly vary over a 24-hour period with postural and diurnal variation unaccounted for in the current study.

Our understanding of glaucoma and vascular involvement in the disease process continues to evolve. Moving forward, the inclusion of novel biomarkers to understand overall glaucoma risk, especially if possible through non-invasive monitoring of vascular health, may provide improvements to individual diagnosis, disease management, and vision preservation.

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