A recent study says that leafy vegetables such as lettuce, spinach and kale and nitrate-rich vegetables are associated with lowering the risk of primary open-angle glaucoma by 20 to 30 percent.

Glaucoma is a condition which can affect sight, usually due to build up of pressure within the eye because fluid cannot drain away.

This new study found people who ate a nitrate-rich diet had lower levels of primary open-angle glaucoma (POAG), a rare condition which involves chronic or acute sudden painful build-up of pressure in the eye.

The researchers followed up participants biennially in the prospective cohorts of the Nurses' Health Study (63,893 women; 1984-2012) and the Health Professionals Follow-up Study (41,094 men; 1986-2012). Eligible participants were 40 years or older, were free of POAG, and reported eye examinations. Information on diet was updated with questionnaires.

During follow-up, 1,483 incident cases of POAG were identified. Participants were divided into quintiles (one of five groups) of dietary nitrate intake (quintile 5, approximately 240 mg/d; quintile 1, approximately 80 mg/d). The researchers found that greater intake of dietary nitrate and green leafy vegetables was associated with a 20 percent to 30 percent lower POAG risk; the association was particularly strong (40 percent-50 percent lower risk) for POAG with early paracentral visual field loss (a subtype of POAG linked to dysfunction in blood flow autoregulation).

The study has been published in JAMA Ophthalmology.