Effect of intraocular pressure on the hemodynamics of the central retinal artery: a mathematical model

Retinal hemodynamics plays a crucial role in the pathophysiology of several ocular diseases. There are clear evidences that the hemodynamics of the central retinal artery (CRA) is strongly affected by the level of intraocular pressure (IOP), which is the pressure inside the eye globe. However, the mechanisms through which this occurs are still elusive. The main goal of this paper is to develop a mathematical model that combines the mechanical action of IOP and the blood flow in the CRA to elucidate the mechanisms through which IOP elevation affects the CRA hemodynamics. Our model suggests that the development of radial compressive regions in the lamina cribrosa (a collagen structure in the optic nerve pierced by the CRA approximately in its center) might be responsible for the clinically-observed blood velocity reduction in the CRA following IOP elevation. The predictions of the mathematical model are in very good agreement with experimental and clinical data. Our model also identifies radius and thickness of the lamina cribrosa as major factors affecting the IOP-CRA relationship, suggesting that anatomical differences among individuals might lead to different hemodynamic responses to IOP elevation.

Mathematical modeling approaches in the study of glaucoma disparities among people of African and European descents

Open angle glaucoma (OAG) is a severe ocular disease characterized by progressive and irreversible vision loss. While elevated intraocular pressure (IOP) is a well-established risk factor for OAG, the progression of OAG in many cases, despite IOP treatment, suggests that other risk factors must play significant roles in the development of the disease. For example, various structural properties of the eye, ocular blood flow properties, and systemic conditions have been identified as risk factors for OAG. Ethnicity has also been indicated as a relevant factor that affects the incidence and prevalence of OAG; in fact, OAG is the leading cause of blindness among people of African descent. Numerous clinical studies have been designed to examine the possible correlation and causation between OAG and these factors; however, these studies are met with the challenge of isolating the individual role of multiple interconnected factors. Over the last decade, various mathematical modeling approaches have been implemented in combination with clinical studies in order to provide a mechanical and hemodynamical description of the eye in relation to the entire human body and to assess the contribution of single risk factors to the development of OAG. This review provides a summary of the clinical evidence of ocular structural differences, ocular vascular differences and systemic vascular differences among people of African and European descent, describes the mathematical approaches that have been proposed to study ocular mechanics and hemodynamics while discussing how they could be used to investigate the relevance to OAG of racial disparities, and outlines possible new directions of research.

Impaired ocular blood flow regulation in patients with open-angle glaucoma and diabetes

BACKGROUND

  To elucidate the potential impact of diabetes mellitus on primary open-angle glaucoma pathology through vascular deficiency.

DESIGN

  Cross-section analysis from a longitudinal, prospective study.

PARTICIPANTS

  Eighty-four open-angle glaucoma patients (20 diabetic open-angle glaucoma patients and 64 non-diabetic open-angle glaucoma patients)

METHODS

  Patients were analyzed for ocular structure, ocular perfusion pressure (OPP), retrobulbar blood flow and retinal capillary perfusion. Statistical analysis was performed by SPSS version 18.0. Comparisons between groups were made as well as multivariate linear regression analysis.

MAIN OUTCOME MEASURE

  Retrobulbar blood flow and the retinal microcirculation.

RESULTS

  Central retinal artery peak systolic velocity was 13.5% lower in diabetic patients (P = 0.007). In diabetic open-angle glaucoma patients, ocular perfusion pressure positively correlated with central retinal artery and temporal posterior ciliary artery peak systolic velocity (R = 0.476, P = 0.039 and R = 0.529, P = 0.02, respectively), and with central retinal artery and nasal posterior ciliary artery resistance index (R = 0.537, P = 0.018 and R = 0.566, P = 0.012 respectively). Average retinal nerve fibre layer positively correlated with central retinal artery peak systolic velocity and temporal posterior ciliary artery end diastolic velocity (R = 0.501, P = 0.029 and R = 0.553, P = 0.019, respectively), and negatively correlated with superior and inferior retinal avascular space in the diabetic group (R = -0.498, P = 0.030 and R = -0.700, P = 0.001, respectively); no correlations were found in the non-diabetic group. Negative correlations between retrobulbar and retinal circulations were only found in the diabetic open-angle glaucoma patients, whereas positive correlations between retinal flow and non-flow were only found in non-diabetic open-angle glaucoma patients.

CONCLUSION

  Diabetes may interfere with normal vascular regulation and contribute to glaucoma progression.