In a large, retrospective study of the Taiwan population, researchers found individuals with retinal vein occlusion (RVO) demonstrated an adjusted risk increase of 21 percent for suffering a heart attack.

RVO is one of the most common causes of visual impairment, the researchers wrote in PLOS One. It results from thrombosis in the retinal vein and shares many of the same risk factors as acute MI (AMI), but previous studies had been inconsistent in proving a relationship between RVO and AMI.

“The objective of our study is to investigate whether patients with RVO have a higher risk of developing AMI than controls using the ‘whole population’ NHIRD in Taiwan, not ‘sample data’ as reported in previous studies,” wrote lead researcher Yu-Yen Chen and colleagues. “Thus, we will have sufficient statistical power.”

Using the entire National Health Insurance Research Database from 2001 through 2013, the authors identified 37,921 people with RVO and compared them to 113,763 subjects without RVO—a 1:3 ratio. The groups were propensity score-matched based on age, gender, obesity, stroke, hyperviscosity syndrome, glaucoma and the use of antithrombotic drugs.

The mean age of the cohort was 62.4 and both groups had an average follow-up of 5.5 years. During the 13-year study period, AMI occurred in 3.2 percent of RVO patients and 2.3 percent of patients in the comparison group.

After adjustment for confounders, the RVO group had a 21 percent increased risk of developing AMI.

“RVO mainly occurs at arteriovenous crossings where the retinal arteriole and venule share a common adventitia sheath,” Chen et al. wrote. “If the arterial wall is sclerotic, it may compress the underlying vein, and the turbulent blood flow in the vein will facilitate the formation of venous thrombosis and venous occlusion.

“Similarly, the underlying mechanism of AMI involves a sclerotic artery (coronary artery), which causes thrombus formation and venous obstruction. We postulate that RVO and AMI may be associated because the changes in retinal vessels may somehow imply that changes have also occurred in coronary vessels.”

The researchers further divided the RVO group into individuals with central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). Compared to people with neither form of RVO, the adjusted hazard ratios for CRVO and BRVO were 1.35 and 1.15, respectively.

“BRVO and CRVO may not have the same risk factors,” the authors wrote. “To the best of our knowledge, our study is the first to report a significantly higher risk of AMI in the CRVO group compared with the BRVO group.”

Chen and colleagues pointed out the national database didn’t include tobacco use, which is a risk factor for PVO and AMI. Another limitation of the study is some patients with asymptomatic RVO could have gone undetected and been misclassified. However, the authors noted proper classification would, if anything, bolster the association between PVO and increased heart attack risk.

“Clinically, our study reminds ophthalmologists to pay more attention to the risk of AMI when they are treating patients with RVO,” they wrote. “In particular, patients with RVO who have risk factors for AMI, such as diabetes and hypertension, if are not under proper treatment, should be referred to physicians for early diagnosis and treatment to prevent the occurrence of AMI.”