People who smoke, or have smoked a large number of cigarettes over time, are more likely to develop age-related macular degeneration or to have it worsen sooner, according to a long-term study.
Age-related macular degeneration (AMD) is a common eye disease that results in damage to the central part of the retina and is a leading cause of blindness among Americans over the age of 50.
"This study and other studies suggest that the cigarette smoking may increase the chance of macular degeneration worsening, which in turn, can increase the chance of losing central vision," Dr. Neil Bressler told Reuters Health.
Bressler is an ophthalmologist with the Johns Hopkins University School of Medicine in Baltimore. He was not involved in the study.
Bressler explained that macular degeneration leads to scarring or atrophy of the centre of the retina (the macula), the light-sensitive tissue lining the back of the centre of the eye that's responsible for fine vision needed for reading and driving and recognizing faces.
Bressler said the current theory is that smoking might damage blood vessels that nourish the retina, leading to an increased risk of worsening of macular degeneration, or that smoking might deposit toxins within retina tissue that damage its functioning.
Read: Aspirin tied to age-related macular degeneration
Chelsea Myers, a researcher with the department of ophthalmology and visual sciences at the University of Wisconsin School of Medicine and Public Health in Madison led the new study, which was published in Ophthalmology.
Myers and her colleagues used data from the Beaver Dam Eye Study, which began in 1988 and included nearly 5,000 adult residents of Beaver Dam, Wisconsin. Participants were examined at the beginning of the study and follow-up examinations were done every five years.
A total of 4,439 participants were included in the analysis, which found that 24 percent developed early-stage AMD over the course of 20 years, and 4.5 percent progressed to late-stage AMD.
Current smoking was tied to a 36 percent greater risk of progressing from minimal to moderate early AMD. People who smoked the most cigarettes over time had a slightly increased risk of developing minimal early AMD and of going from severe early AMD to late-stage AMD.
Read: How smoking can cause blindness
The authors note that they found no differences among people with a gene mutation linked to higher risk of developing AMD, indicating that smoking may not interact with those genes.
The study does not prove that smoking causes AMD or speeds its progression, or that quitting smoking will prevent or slow the disease.
But, the authors write, the results have important healthcare implications because smoking is a modifiable behaviour.
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Image: Italian man smoking on the street from Shutterstock