The University of Newcastle, Australia has helped the World Health Organization (WHO) develop a new summary of evidence for eyecare professionals showing the association between tobacco use and vision loss.
The document – published on 12 October – is the fifth in a series of Tobacco Knowledge Summaries that ophthalmologists, optometrists and other eyecare professionals can use as an advocacy tool in the fight for tobacco control and prevention of tobacco related adverse health effects.
The International Agency for the Prevention of Blindness also helped develop the resource, which focuses on the link between smoking and noncommunicable eye diseases including cataract, glaucoma and age-related macular degeneration (AMD).
“With a single breath, the hundreds of toxins in tobacco smoke begin damaging the lungs. These toxins then pass from the lungs to the bloodstream and to various organs throughout the body, including the eyes,” the summary stated.
“In addition to the impact of tobacco smoking on the development of eye disease in the user, tobacco smoke irritates the eyes and worsens dry eye syndrome in smokers and bystanders exposed to second-hand smoke, particularly among those who wear contact lenses.”
In AMD, smoking is said to be “the primary modifiable risk factor”. Tobacco smoking generates a local inflammatory response, and cigarette smoke is a strong oxidant. Furthermore, oxidative stress was found to be one of the primary mechanisms for smoking-related damage to retinal structures, contributing to the development and progression of AMD.
“[A meta] analysis found a fourfold increase in risk for neovascular AMD and a twofold-to-threefold increase in the risk of atrophic AMD associated with smoking,” the report said.
“Smokers also have a greater risk of developing AMD at a younger age. A study conducted in 2019 found that current smokers developed AMD 5.5 years earlier than never smokers, and 4.4 years earlier than ex-smokers.”
In terms of cataracts, one prospective cohort study (in 44,000 men) found current smokers of more than 15 cigarettes per day had a 42% increased risk of undergoing cataract extraction compared with never smokers.
“Studies have shown that smoking appears to generate free radicals, which raises the oxidative stress in the lens of the eye. This lowers the concentration of plasma in antioxidants, inhibiting their ability to discard damaged proteins. Cataracts develop when these proteins build up in the lens causing vision loss, and surgical removal of the cloudy lens and replacement with an artificial lens is the only option to restore vision,” the summary said.
New evidence also suggests that smoking may increase the incidence of glaucoma.
According to the WHO document, one study followed a cohort of smokers for 8.5 years, recording their smoking habits and recording the incidence of glaucoma. After controlling for potential confounders, current smokers were found to be at increased risk of developing glaucoma as compared with never smokers.
Impacts of second-hand smoke
The report also delved into the impact of second-hand smoking, which is responsible for 1.2 million of the 8 million tobacco exposure related deaths each year.
In terms of eye health, it highlighted a study conducted at the University of Cambridge and University College London demonstrating that individuals who live with a smoker for at least five years are twice as likely to develop AMD as those who do not.
[Another] study conducted at the Chinese University of Hong Kong Eye Centre in 2019 examined the impact of second-hand smoke on a cohort of children between six and eight years old, a third of whom had been exposed to second-hand smoke,” the summary said.
“Scientists measured the thickness of the choroid, which is the part of the eye that thins when exposed to tobacco smoke, and found that children who had been exposed to second-hand smoke experienced choroidal thinning of between 6 μm and 8 μm. This thinning can slow or completely stop choroidal blood flow, which leads to future vision loss associated with macular degeneration.”
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