Study explores influence of ocular blood flow in course of glaucoma
New techniques shed light on roles of blood, perfusion pressure in ocular blood flow
Many other factors, including demographic influences and individual susceptibilities, also make it challenging to study relationships between ocular blood flow and glaucoma.
To overcome the multiple confounders, Dr. Harris and colleagues have proposed using a mathematical model to leverage the analogy between blood flow in a network of vessels and current flow in a circuit.
The model calculates ocular blood flow taking into account vascular regulation, cerebrospinal fluid pressure, blood pressure, venous blood pressure, and IOP.
He illustrated its performance by describing its application for determining how changes in IOP and blood pressure affect retinal blood flow. Inputs for the model included three theoretical patients with different blood pressures (low, normal, and high) and IOP values ranging from 15 to 45 mm Hg.
According to the model, retinal blood flow was unchanged for IOP values < 26 mm Hg in the theoretical patients with high or normal blood pressure.
The plateau was explained by autoregulation. However, retinal blood flow continued to increase with decreasing IOP in the patient with low blood pressure.
The calculations also showed that when IOP was > 36 mm Hg, the predicted decrease in retinal blood flow decreased at a steeper slope compared with lower IOP levels as a result of partial venous collapse.
The venous collapse started earlier (at a lower IOP) in the theoretical patient with low blood pressure compared with the normal and high blood pressure patients.
“These data explain the findings of population-based studies showing that decreased blood pressure and decreased perfusion pressure are independent risk factors for glaucoma,” Dr. Harris said.
Alon Harris, PhD
This article was adapted from a presentation delivered by Dr. Harris at Glaucoma Subspecialty Day preceeding the 2016 American Academy of Ophthalmology meeting. He has no relevant financial interests to disclose.