A new study published in Acta Ophthalmologica has linked diabetic retinopathy (DR) with cardiovascular disease (CVD), finding that DR patients were at higher risk of CVD—and vice versa.
Give me some background first.
Type 1 diabetes affects 8.4 million people worldwide, and the long-term prevalence of DR—which can potentially result in vision loss—in type 1 diabetes is 97%.
To note, however: Existing research on the connection between DR and CVD—a major cause of mortality—have largely focused on type 2 diabetes.
Now, talk about the study.
This longitudinal, matched case-cohort study was conducted in order to investigate DR as a potential marker for CVD.
To identify the cohort for the study, researchers used four databases:
- The Danish Registry of Diabetic Retinopathy (DiaBase)
- Mandatory database for national DR screening program
- The Danish Civil Registration System
- Used to link patient data via the Central Personal Registration number
- The Danish National Patient Registry (DNPR)
- Used to identify CVD patients via ICD-10 codes
- The Danish National Prescription Registry
- Used for prescription information in the period 1995-2018
Who was included in the study?
Researchers used the databases to identify cases of adults with type 1 diabetes (as evidenced by ICD-10 codes and filled prescriptions), resulting in 16,547 cases.
These cases were matched with five individuals per birth year and sex, which resulted in a case ratio of 1:4.87.
The final study population contained 98,946 people and 372,617 combined person-years at-risk over the 5 years of observation.
What about CVD?
CVD was defined with the following major categories:
- myocardial infarction
- arteriosclerotic heart disease
- coronary artery bypass grafting surgery
- heart failure
- pulmonary hypertension
- cardiac arrhythmias
- aortic diseases
- vascular disease
The prevalence of CVD at the index date of the study was compared between the cases and the references. Then, patients with prevalent CVD were excluded and CVD incidence over the course of the study was compared between cases and references.
The final stage of the study involved comparing the development of CVD among patients with DR to those without—and comparing the development of DR among diabetic patients with CVD to those without.
Findings?
Adults with any level of DR had a higher risk of developing CVD compared to those without.
Furthermore, the risk of developing CVD grew with each increasing level of DR (as measured by the International Clinical Diabetic Retinopathy Disease Severity Scale.
Finally, the 537 patients with type 1 diabetes and prevalent CVD but no DR had a higher risk of incident DR than those without CVD.
Expert opinion?
While the study did not investigate a causal relationship, the authors suggested that potential explanations could include:
- Shared pathogenic pathways
- DR signs reflecting systemic disease processes
- Systemic microvascular disease igniting a cascading inflammatory response
Limitations?
The authors noted that while the strengths of the study included access to an entire national database of DR screenings, the databases used did not include records of lifestyle factors and, as a registry study, was vulnerable to coding error.
Take home.
“Results from this nationwide matched case–cohort study indicate DR as a useful marker of CVD in type 1 diabetes with increasing risk demonstrated for higher levels of DR,” wrote the study authors. “Likewise, CVD also independently predicted upcoming DR.”
Future studies, they argued, could explore early preventive interventions and the connection between DR and CVD in patients with type 2 diabetes.