Our eyes connect us to the outside world, and offer a window to everything that moves around us. Glaucoma, however, can steal this ability away. According to a new study published in JAMA Ophthalmology , many of the three million Americans currently living with glaucoma may have been able to prevent their disease altogether, if only they had eaten a healthier diet filled with green leafy vegetables.

For the study, researchers looked at the diets and eye exam results of nearly 105,000 participants (mostly women) from 1984 to 2012. At the time the study began, participants were at least 40 years old and free from primary open-angle glaucoma — the most common form of the disease. The researchers divided participants into five groups based on varying levels of green leafy vegetable consumption (known as dietary nitrates). Over the course of the study, participants underwent eye exams every two years, and 1,483 participants were ultimately diagnosed with glaucoma, which causes blindness if left untreated.

"We found those consuming the most green leafy vegetables had a 20 to 30 percent lower risk of glaucoma," said the study’s lead researcher Jae Kang, a professor at Brigham and Women's Hospital and Harvard Medical School, according to HealthDay. "In glaucoma, we think there is an impairment of blood flow to the optic nerve. An important factor that regulates blood flow to the eye is a substance called nitric oxide. When you consume the higher amount of green leafy vegetables, you have greater levels of nitric oxide in your body.”

Those who ate the highest levels of green leafy vegetables — about 1.5 servings a day — were less likely to develop glaucoma, the study found. It also revealed people with glaucoma had impaired nitric oxide production in the eye, prompting researchers to recommend higher consumption of these vegetables, especially among those at risk of the disease. People with a family history of glaucoma, those over the age of 60, and African-Americans over the age of 40 are at highest risk, according to the National Eye Institute.

Contrary to popular belief, experts know carrots aren’t the best dietary source for better vision — it’s actually leafy greens. The American Optometric Association says it’s because these greens are packed with the antioxidants lutein and zeaxanthin, which have been shown to reduce the risk of chronic eye diseases, such as glaucoma, cataracts, and age-related macular degeneration.

So if you’re at risk of glaucoma, turn to foods like spinach, kale, collard greens, celery, broccoli, lettuce, green peas, and Brussels sprouts, which are packed with the antioxidants. Don’t like them? Nutrition supplements may also help. Any of these options will go toward reducing your risk of vision impairment in the future.

Source: Kang JH, et al. Intakes of Lutein, Zeaxanthin, and Other Carotenoids and Age-Related Macular Degeneration During 2 Decades of Prospective Follow-up . JAMA Ophthalmology. 2016.