Women who use oral contraceptives for several years need to consider having their eyes checked more regularly as they get older. New research suggests that the pills may double their lifetime risk of developing glaucoma, a degenerative eye disease that can cause blindness if left untreated.

The researchers cautioned that their findings should not discourage women from using oral contraceptives, since the risk of glaucoma for the average adult over the age of 40 remains fairly low.

Researchers have previously found that women who enter menopause early or take medications that block estrogen, also have an elevated risk of glaucoma.

The new study looked at data on 3,406 women over the age of 40. The women regularly underwent eye exams and answered questions about their reproductive health and medical histories.

Women who reported having used birth control pills of any kind for three years or longer had a 5 percent risk of developing glaucoma, compared with a risk of about 2.5 percent in the general population, Well reports.

Together with data from previous studies they suggest that there is a relationship between estrogen levels and the development of eye disease.

A growing body of evidence suggests that women who go into menopause early or have their ovaries removed are also at slightly greater risk of glaucoma. Estrogen appears to have a “maintenance effect” on retinal ganglion cells in the eye, which are known to have estrogen receptors.

Ophthalmologists generally recommend annual eye screenings for people 65 and older.