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Editors Selection IGR 7-2

Clinical Examination Methods: Ocular blood flow and lamina cribrosa measures

Comment by Alon Harris on:

92028 Associating the biomarkers of ocular blood flow with lamina cribrosa parameters in normotensive glaucoma suspects. Comparison to glaucoma patients and healthy controls, Krzyżanowska-Berkowska P; Czajor K; Iskander DR, PLoS ONE, 2021; 16: e0248851

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Current advancements in non-invasive imaging technologies, including optical coherence tomography angiography (OCT-A), have allowed for more precise visualization of ocular structures and improved understanding of their relationship(s) to physiological alterations in hemodynamics and tissue metabolism. Historically, population-based studies have identified lower ocular perfusion pressure to be an independent risk factor for open-angle glaucoma (OAG), while a wide variety of custom modalities and imaging applications have shown many aspects of the ocular circulation to be lower in glaucoma patients compared to healthy controls.¹

While evidence of vascular deficit in glaucoma continues to be confirmed, especially in certain population groups, the relationship of ocular vascular biomarkers to lamina cribrosa structure is significantly less well defined

While evidence of vascular deficit in glaucoma continues to be confirmed, especially in certain population groups, the relationship of ocular vascular biomarkers to lamina cribrosa structure is significantly less well defined with many critical structures involved in glaucoma progression previously being difficult or impossible to directly visualize.

Krzyżanowska-Berkowska and colleagues contribute novel data on retrobulbar blood flow biomarkers using color Doppler imaging and their relationship with lamina cribrosa structure including depth, deflection depth, lamina cribrosa shape index and its horizontal equivalent (LCSIH) on B-scan images via OCT. The authors found a consistency in lower biomarker values of the ophthalmic and central retinal arteries in OAG patients compared to controls, but only a single statistically significant difference (peak systolic velocity [PSV] in central retinal artery [P = 0.011]]) in comparison to (normotensive) glaucoma suspects. Importantly, the authors also identified several statistically significant associations between LCSIH and several retrobulbar blood flow biomarkers in glaucoma patients, but not in glaucoma suspects and healthy controls. The authors conclude that deformation of lamina cribrosa is associated with lower retrobulbar blood flow biomarkers in OAG patients, while a similar structure of the lamina cribrosa was not associated ocular blood flow biomarkers in glaucoma suspects.

Strengths of the study include the fairly robust sample size (70 OAG, 72 suspects, 69 controls) and having all groups matched for age, intraocular pressure, and central corneal thickness. A significant limitation of the study is the use of Doppler imaging to study the supplying vessels instead of the localized tissue perfusion and metabolism.

A significant limitation of the study is the use of Doppler imaging to study the supplying vessels instead of the localized tissue perfusion and metabolism

Careful interpretation of Doppler assessed blood flow velocities in the retrobulbar space is also required since quantification of blood flow is not usually possible due to lack of vessel diameter. For instance, an increasing PSV without accompanying alterations in diastolic velocity or vascular resistance may indicate stenosis downstream from the site of measure. OCTA imaging of blood flow and vascularity in the optic nerve head and retinal blood may allow for more precise relationships to be identified in tissues adjoining to the lamina cribrosa, as opposed to upstream blood vessels. Additionally, longitudinal data on how these group differences influence OAG conversion (suspects) and progression would add significant meaning to the author's cross-sectional observations. In the future, precision medical approaches that consider and model for individualized risk factors and demographic susceptibilities may be able to integrate ocular hemodynamics into an overall risk model to improve OAG disease management.

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