Cooking with wood or coal can increase the risk of major eye diseases that can lead to blindness, according to a study involving nearly half a million people in China.

The study led by a team of international researchers from the University of Oxford and the Chinese Academy of Medical Science and Peking University, Beijing, showed that long-term use of solid fuels for cooking was associated with conjunctiva (32 percent), cataracts (17 percent), and disorders of the sclera, cornea, iris and ciliary body (DSCIC - 35 percent), compared with those who cooked using clean fuels.

Individuals who switched from using solid to clean fuels for cooking had smaller elevated risks (over those who had always used clean fuels) compared to those who did not switch. People who switched had 21 percent, 5 percent, and 21 percent higher risk for conjunctiva, cataracts, and DSCIC, respectively, according to the results published in the journal PLOS Medicine.

"The increased risks may be caused by exposure to high levels of fine particulate matter (PM2.5) and carbon monoxide, which can damage the eye surface and cause inflammation," said lead author Dr. Peter Ka Hung Chan, research fellow in the Nuffield Department of Population Health at Oxford.

Burning wood also increases the risk of eye injury from sparks or wood dust.

Further, there was no association found between solid fuel use and risk of glaucoma, because this disorder affects internal eye structures, which are less exposed to pollutants in the air, the researchers said.

"Among Chinese adults, long-term solid fuel use for cooking was associated with higher risks of not only conjunctiva disorders but also cataracts and other more severe eye diseases. Switching to clean fuels appeared to mitigate the risks, underscoring the global health importance of promoting universal access to clean fuels," Zhengming Chen, Professor of Epidemiology and Director of China Programmes at the Nuffield.