Millions of people in the UK are putting their sight at risk by continuing to smoke, warn specialists.Despite the clear connection, only one in five people recognise that smoking can lead to blindness, a poll for the Association of Optometrists (AOP) finds.Smokers are twice as likely to lose their sight compared with non-smokers, says the RNIB.That is because tobacco smoke can cause and worsen a number of eye conditions. How smoking can harm your eyesCigarette smoke contains toxic chemicals that can irritate and harm the eyes.For example, heavy metals, such as lead and copper, can collect in the lens - the transparent bit that sits behind the pupil and brings rays of light into focus - and lead to cataracts, where the lens becomes cloudy.Smoking can make diabetes-related sight problems worse by damaging blood vessels at the back of the eye (the retina).Smokers are around three times more likely to get age-related macular degeneration - a condition affecting a person's central vision, meaning that they lose their ability to see fine details.And they are 16 times more likely than non-smokers to develop sudden loss of vision caused by optic neuropathy, where the blood supply to the eye becomes blocked. In the poll of 2,006 adults, 18% correctly said that smoking increased the risk of blindness or sight loss, while three-quarters (76%) knew smoking was linked to cancer.The AOP says stopping or avoiding smoking is one of the best steps you can take to protect your vision, along with having regular sight checks.Aishah Fazlanie, Optometrist and Clinical and Regulatory Adviser for the AOP, said: "People tend to know about the link between smoking and cancer, but many people are not aware of the impact that smoking can have upon the eyes."Smoking increases the risk of sight-threatening conditions, such as age-related macular degeneration, which is an important reason why smokers should consider quitting."Fewer smokersIn the UK, 17% of men and 13% of women - around 7.4 million people - are smokers. More than half (61%) of them say they want to quit.Figures from the Office for National Statistics show the proportion of current smokers has been decreasing, with the largest fall since 2011 occurring among 18 to 24-year-olds.In 2017, around 2.8 million people - 5.5% of the UK - were using e-cigarettes, and the most common reason given for vaping was to help quit smoking.