Researchers from the University Clinic for Clinical Pharmacology at the Medical University of Vienna have identified new evidence supporting the connection between reduced oxygen transport to the retina with the development of diabetic retinopathy (DR).
Give me some background.
Finely-ramified blood vessels that supply the retina also manage gas exchange and metabolism in tissues across the body. Their conditions can determine certain eye diseases and medical conditions, including type 2 diabetes.
Talk about the study.
The clinical study enrolled 67 patients with an average age of 65 who had been diagnosed with type 2 diabetes and different stages of nonproliferative DR.
The participants were compared to a control group of 20 patients who did not have diabetes. Of the total, 34 patients did not have DR; 15 had mild DR; and 18 had moderated to severe DR.
How was retinal oxygen measured?
Researchers used the oxygen module of a retinal vessel analyzer to measure the total retinal blood flow (TRBF) and oxygen saturation within the retina of each patient via a data measurement conversion (using Doppler optical coherence tomography [OCT]).
What did they find?
They observed that, as the severity of diabetes increases, less oxygen is able to travel from the blood into the tissue. However, it was also found that less oxygen was supplied to the retina in the diabetic patients who did not yet show any visible changes in the retina.
According to the investigators, “This means that the gas exchange was already compromised before the damage was clinically diagnosable.”
Give me some numbers.
TRBF was found to be higher in patients with no DR (40.1 ± 9.2 μL/min) and mild DR (41.8 ± 15.0 μL/min) than in healthy patients (37.2 ± 5.7 μL/min) and patients with moderate to severe DR (34.6 ± 10.4 μL/min).
Additionally, retinal oxygen extraction was highest among healthy patients (2.24 ± 0.57 μL O2/min), followed by those with no DR (2.14 ± 0.6 μL O2/min); mild DR (1.90 ± 0.77 μL O2/min); and moderate to severe DR (1.78 ± 0.57 μL O2/min, P = 0.040 vs. healthy patients).
Any limitations?
The authors note that the study’s cross-sectional format meant that they could not determine whether the reduction in oxygen extraction observed in type 2 diabetes patients is a cause or consequence of the disease.
Further, they stated that they could not fully exclude factors such as diabetes duration, glucose levels, or blood pressures, which could partially influence results.
Significance?
According to the study authors, this research is the first to demonstrate that retinal oxygen extraction is reduced in patients with type 2 diabetes and those suffering from moderate to severe DR.
Take home.
While the data indicates that oxygen metabolism impairment is reliant on the disease severity, the authors recommend that further longitudinal studies are needed to assess whether oxygen saturation may be a biomarker in the future to identify high-risk patients.