Accumulated lead exposure may increase the risk of developing a cataract, research suggests.
Cataracts are a leading cause of sight problems
Scientists at Boston's Brigham and Women's Hospital found people with the highest level of lead in their bones were most likely to develop a cataract.
Cataracts, the leading cause of blindness world-wide, are a clouding of the lens, the clear tissue which focuses light on to the retina.
The study is published in the Journal of the American Medical Association.
Despite measures to cut lead pollution, most adults have substantial levels in their bodies.
Previous research has indicated that low-level lead exposure may increase the risk of a number of chronic age-related diseases.
The Boston team investigated whether there was an association between the development of cataracts and lead levels in two bones - the tibia (shin bone) and the patella (kneecap).
Data was analysed on 642 male patients, or which 122 developed a cataract.
The researchers found that men with the highest tibia lead level were 2.7 times more likely to develop a cataract than those who recorded the lowest level of lead in this bone.
When other factors, such as smoking and diabetes were taken into consideration, the risk rose to 3.2 times that of those exposed to the lowest lead levels.
The research also found an increased risk among patients who recorded the highest patella lead levels - but the trend was not significant.
Blood lead levels, more indicative of short-term exposure levels, were not significantly associated with cataract.
Writing in JAMA, the researchers said they believe their study provides the first evidence suggesting accumulated lead exposure, such as that commonly experienced by adults in the US, may be an important, unrecognized risk factor for cataract.
Researcher Dr Debra Schaumberg told the BBC News website: "There are laboratory data, including from animal studies, showing that lead can get into the lens, and that once there it is toxic.
"In particular, lead interferes with the normal oxygen balance and causes oxidative stress leading to changes in lens proteins that can affect lens clarity and transparency and thus cause cataract.
"Another possible mechanism might be that lead may also interfere with the normal calcium balance in the lens."
Dr Schaumberg said the results suggested that lead exposure contributed to 42% of all cataracts.
"If these data are relevant to other areas of the world then it seems logical that reduction of lead exposure could have a significant impact on cataract development globally."
Anita Lightstone, head of eye health for the Royal National Institute for the Blind said lead exposure was harmful for many reasons and should be avoided.
However, she said: "We would not wish people to be unduly alarmed as in a large number of cases cataracts can be removed with an operation and by use of an artificial lens, good vision can be restored.
"RNIB also recommends that everyone have their eyes tested once every two years, for early detection of eye conditions such as cataracts."