E-cigarettes damage user’s eyesight, a major US study has suggested, in the latest evidence undermining claims the devices are a safe alternative to smoking.

Scientists in California found that current vapers were 34 per cent more likely to suffer from visual impairments compared to those who had never tried it, with former vapers 14 per cent more likely.

Researchers believe the solvents in e-cigarette liquid may damage the tear duct, as well as causing the body “oxidative stress”, which has been linked to ocular deterioration.

It has long been known that traditional cigarettes can harm people’s eyesight.

However, e-cigarettes have been promoted in the UK as being significantly safer, with the Government stating they are at least 95 per cent less damaging.

Their popularity has exploded, especially among the young, despite health officials advising that the devices should only be used by current smokers as a means of quitting.

E-cigarette users grew from 700,000 in 2012 to 3.6m in 2021

The number of e-cigarette users grew from around 700,000 in 2012 to 3.6 million in 2019, falling to 3.2 million in 2020, before increasing again in 2021 to 3.6 million, according to the campaign group Ash.

Last year the World Health Federation described the growth in e-cigarette use as an “epidemic”.

Set up as a snapshot survey, the new study by the University of California included 1,173,646 adults in the US aged between 18 and 50. Between 2016 and 2018 they were asked in a questionnaire if they smoked, vaped, and whether or not they suffered from visual impairment. The results are published in the American Journal of Ophthalmology.

E-cigarettes deliver an aerosolised liquid composed of nicotine, flavourings, and solvents such as propylene glycol or glycerin.

Because traditional cigarettes have such a complex chemical makeup – the smoke contains more than 4,000 different chemicals – scientists have struggled to pinpoint what causes harm to vision.

However, a 2019 Malaysian study showed a correlation between e-cigarette use and increased symptomatic dry eye and decreased tear film quality.

The authors speculated that the propylene glycol solvent in the vape liquid produces free radicals that damage the lipid layer of the tear film. The vapers in the study were found to have elevated levels of reflex tearing.

Another theory is that e-cigarettes prompt oxidative stress and a reduction in antioxidants, which has been implicated in the development of cataracts, age-related macular degeneration, and even glaucoma.

‘Nasty toxins in e-cigarette vapour’

Professor Simon Capewell, a clinical epidemiologist at the University of Liverpool and not associated with the new study, said: “There is a clear association between smoking lit cigarettes and visual impairment.

“There are also many nasty toxins in e-cig vapour.

“It will therefore be important for doctors and other researchers to carefully assess the onset of new visual impairment in vapers, especially those who have never used lit cigarettes.”

He cautioned that the study does not prove a causal link between vaping and harm to vision.

In 2020, the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment, a independent body advising the UK Government, found in a report that while switching from smoking to e-cigarettes would be likely to reduce overall health risks, non-smokers who took up vaping would be subject to risks they otherwise would not face.

The same year scientists at Virginia Commonwealth University attacked Public Health England’s 95 per cent claim as misleading and outdated because e-cigarettes had changed significantly.

The UK Government is widely regarded as an international outlier in its relative enthusiasm for vaping as a means for reducing smoking.

Supporters argue that the approach has succeeded in increasing rates of those quitting tobacco, while ensuring vape products are not marketed directly to young people.

E-cigarettes are associated with significant adverse cardiorespiratory and immunological changes, a study published last year found.

Evidence shows the devices increase blood pressure, heart rate and arterial stiffness.