Japanese men with higher blood pressure were more likely to have impaired color vision, a new study has found.

Researchers said that for now, it’s not clear what explains the findings.

According to Dr. Saadia Rashid, damage to certain parts of the eye that occurs as a result of high blood pressure could ultimately lead to vision loss. It’s possible that impaired color vision could be a sign of future problems related to high blood pressure, also known as hypertension, said Rashid, an ophthalmologist from Montefiore Medical Center in New York.

But the new study represents just a snapshot in time, and longer-term studies are needed to tease out the relationship, she said.

“It will be great if acquired color vision impairment can be a harbinger of future hypertension-related complications, however it is premature to state that,” Rashid told Reuters Health. She was not involved in the research.

Knowing that high blood pressure has been tied to certain eye diseases, Dr. Takuhei Shoji from Saitama Medical University in Japan and colleagues evaluated the relationship between color vision and eye disease, heart-related risk factors and lifestyle habits.

The researchers recruited men ages 20 to 60 years old who were on active duty in the Japanese Self Defense Force in Kyoto.

Shoji’s team looked at the men’s medical records, measured their blood pressure and gave them two tests to assess how accurately they could see and discriminate different colors. Both tests involve lining up a certain number of caps in order of hue.

Of the 872 men included in the study, 130 failed one test and 31 failed the other.

After the researchers took into consideration other factors such as men’s weight, cholesterol, blood sugar levels and other eye diseases, they found that as blood pressure values rose, the odds of having impaired color vision increased as well.

The researchers note that the study design does not allow them to look at changes in vision or blood pressure over time. The study also can’t prove high blood pressure caused impairments in color vision.

Still, “The data are useful and important for further investigations of many of these associations,” the authors write in the American Journal of Hypertension.

“Color vision testing is a higher order visual function and the authors have suggested looking into it as a future early marker of hypertensive disease,” Rashid said.

She said it’s possible that by lowering their blood pressure people could reverse acquired color vision problems, but more research is necessary to determine that as well.

One concern she has is that tests for color vision function are more complicated than the regular eye tests most people get at the doctor. Color vision tests are time consuming and hard to do because they require specific lighting conditions, so they’re not readily available.

“Future research is needed to popularize this idea, and perhaps come up with simpler ways of checking color vision, on modalities such as home smartphones and devices as a home screening tool,” Rashid said.

“We have to wait for the research to catch up,” Rashid added. In the meantime, she said, controlling high blood pressure is “critical” to prevent vision problems and other complications.

She said people can screen their color vision at home with an online color test challenge, such as the one online. The challenge is similar to the tests used in this study.

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