Study: Reduced Oxygen Transport to the Retina Contributing to Damage to the Fine Blood Vessels Causes Diabetic Retinopathy
Researchers in Austria have now found evidence for a previously suspected connection: reduced oxygen transport to the retina contributes to damage to the fine blood vessels, causing diabetic retinopathy. A common complication of diabetes, this retinal damage can ultimately lead to blindness. Even before vision deteriorates, gas exchange in the eye is restricted.
The research, led by Gerhard Garhöfer, MD, of the University Clinic for Clinical Pharmacology at the Medical University of Vienna, said that these finely ramified vessels supplying the retina manage gas exchange and metabolism in tissues all over the body, from the kidneys to the toes. The condition they are in can indicate not only diseases of the eye, but also various other medical conditions. One such disease is widespread type 2 diabetes, a form of this severe metabolic disorder that is strongly linked to age and lifestyle.
Damaged and overstrained microvessels
Diabetic retinopathy occurs in about half of patients with type 2 diabetes who have had the disease for a long time and/or whose sugar levels are poorly managed. The high blood sugar level causes damage to the blood vessels and prevents them from doing their job. Although new blood vessels are formed in response to the lack of oxygen in the retina, these are not functional and increasingly impair vision. As type 2 diabetes is strongly on the rise, doctors also expect to see an increasing number of cases with this secondary disease. In its atlas, the International Diabetes Federation estimates that in 2019, 9.3% of the global population, or 463 million people, suffered from diabetes–mainly in cities and countries with higher average incomes. By 2030, that number is expected to rise to 10.2% (578 million). It often takes time for the diagnosis to be made: one in two diabetes patients are not aware of having the disease.
Contact-free measurement techniques
Dr. Garhöfer’s clinical study involved 70 type 2 diabetics with an average age of 65 without or with different degrees of advanced retinal damage. They were compared with a control group of 20 individuals without diabetes. Since one cannot directly measure oxygen extraction from the blood into the tissue, blood flow and oxygen saturation in the retina of the patients were measured with a contact-free technique. In a precursor project, a mathematical model had already been developed to convert the data from the measurements (using Doppler optical coherence tomography and oximetry) into values for oxygen extraction into the tissue.
"Our results show that with increasing severity of the disease, less and less oxygen finds its way from the blood into the tissue," Dr. Garhöfer said in a news release. "On the other hand, we found that even in type 2 diabetics who did not yet show any visible changes in the retina, less oxygen was already supplied to the retina. This means that the gas exchange was already compromised before the damage was clinically diagnosable.”
"The study results confirm that oxygen delivery to the retina is reduced in patients with diabetes. The measured parameters could help to identify high-risk patients and to instruct them better in terms of therapy and compliance. Gerhard Garhöfer also plans to apply this technique to other diseases, such as neurodegenerative eye diseases," Dr. Garhöfer said.
Publications
Hommer N., Kallab M., Schlatter A. et al.: Retinal oxygen metabolism in patients with type II diabetes and different stages of diabetic retinopathy, Diabetes 2022.
Hommer N., Kallab M., Schlatter A. et al.: Neuro-vascular coupling and heart rate variability in patients with type II diabetes at different stages of diabetic retinopathy, Frontiers in Medicine (Lausanne) 2022.