Eye Expert Statement
Age-related macular degeneration (AMD), also termed age-related maculopathy (ARM), is the leading cause of blindness in Australia1-3. Its prevalence rises from less than 0.5% of people in their forties or fifties to around one in three of those aged in their nineties. People with AMD generally retain some mobility if their peripheral vision is maintained, but they are unable to read, drive or recognise people’s faces. Unfortunately, conventional laser treatment benefits only a small minority of people with AMD. The newer photodynamic therapy is likely to be helpful for well under half of the cases presenting, cannot reverse visual loss in most cases, is very costly and its long-term efficacy is not yet known. Until safe and effective treatments for AMD can be developed, primary prevention measures must be considered.
Based on data from two large population-based Australian studies4,5, there are currently around 34,500 people aged over 50 with legal blindness in Australia. Of these, around 80% are due to AMD4. Two late stage AMD lesions causing visual loss have been defined; a neovascular lesion (neovascular AMD) characterised by macular bleeding and scarring, responsible for two thirds of cases and an atrophic macular lesion (geographic atrophy), which accounts for the remaining third2.
Recent population-based cross-sectional data from four countries6-9 including Australia10 together with data from two large cohort studies11,12, have consistently identified smoking as the strongest environmental risk factor for AMD. All of these studies have shown that current smoking confers a greater risk than past smoking with the risk increased by between 2 and 5-fold. Several studies have demonstrated a dose response with pack years of smoking9,11,12 and a decreased risk with longer duration since cessation7. Evidence of a gradient between amount smoked and ARM severity has also been shown7,10. Although the Macular Photocoagulation Study report13 did not find an association between a history of current smoking at baseline and new cases of AMD, recurrences of the AMD lesions after laser were almost inevitable in persons who continued to smoke (85%), compared with non-smokers (50%). In longitudinal data reported from the Beaver Dam Eye Study14, smoking was related to the incidence of large drusen, the principal precursor lesion for late stage AMD lesions15 in both men and women. Data from the Australian Blue Mountains Eye Study presented at the 2000 Association for Vision & Ophthalmology meeting indicated that smoking was significantly associated with the incidence of atrophic AMD and precursor early age-related maculopathy lesions, particularly macular pigmentary changes16. Mechanisms for the smoking-AMD link are not known, but smoking may have a direct toxic effect on retinal cells and may cause vasoconstriction in the retina. Smoking is also known to reduce the absorption of protective antioxidants from the diet as well as reducing the density of protective macular pigments.
Although only a small proportion of older Australians are still smoking, smokers are disproportionally represented among cases of AMD. Researchers from the Blue Mountains Eye Study in New South Wales estimate that around 20% of AMD can be attributed to smoking17. This includes more than 20,000 of the estimated 100,000 current AMD cases in Australia and more than 8,000 Australians whose blindness from AMD can be attributed to their smoking. Unpublished data from the Visual Impairment Project in Victoria suggest that 14% of AMD is due to smoking.
The public should be educated about the risk of AMD and vision impairment due to cigarette smoking. A new cigarette pack warning about this link has been proposed17. Research from the Visual Impairment Project identified the fear that people have of losing their eyesight18. When asked to identify which of five disabilities that they would first provide treatment and support, 58% of Melbourne participants aged 40 years and older nominated "total blindness", the next most common being paralysis on one side due to a stroke (21%). This fear of blindness may be able to be used to successfully encourage people to quit smoking and discourage people from beginning to smoke. At present, this is the primary prevention strategy for AMD with greatest potential.
This paper has been written with the assistance of:
Assoc Prof Paul Mitchell
Save Sight Institute
University of Sydney, Australia
Prof Hugh Taylor
Managing Director
Centre for Eye Research Australia
Assoc Prof Cathy McCarty
Centre for Eye Research Australia
Dr Wayne Smith
The National Centre for Epidemiology and Population Health
Australian National University
References
1. Cooper RL. Blind registrations in Western Australia: a five year study. Aust N Z J Ophthalmol. 1989;107:875-879.
2. Mitchell P, Smith W, Attebo K, Wang JJ. Prevalence of age-related maculopathy in Australia. The Blue Mountains Eye Study. Ophthalmology. 1995;102:1450-1460.
3. Weih LM, Van Newkirk M, McCarty CA, Taylor HR. Age-specific causes of bilateral visual impairment. Arch Ophthalmol. 2000;118:264-269
4. Attebo K, Mitchell P, Smith W. Visual acuity and the causes of visual loss in Australia. The Blue Mountains Eye Study. Ophthalmology. 1996;103:357-364.
5. Taylor HR, Livingston PM, Stanislavsky YL, McCarty CA. Visual impairment in Australia: distance visual acuity, near vision, and visual field findings of the Melbourne Visual Impairment Project. Am J Ophthalmol. 1997;123:328-337.
6. Klein R, Klein BE, Linton KL, DeMets DL. The Beaver Dam Eye Study: the relation of age-related maculopathy to smoking. Am J Epidemiol. 1993;137:190-200.
7. Vingerling JR, Hofman A, Grobbee DE, de Jong PT. Age-related macular degeneration and smoking. The Rotterdam Study. Arch Ophthalmol. 1996;114:1193-1196.
8. Klaver CC, Assink JJ, Vingerling JR, Hofman A, de Jong PT. Smoking is also associated with age-related macular degeneration in persons aged 85 years and older: The Rotterdam Study [letter]. Arch Ophthalmol. 1997;115:945
9. Delcourt C, Diaz JL, Ponton Sanchez A, Papoz L. Smoking and age-related macular degeneration. The POLA Study. Pathologies Oculaires Liees a l'Age. Arch Ophthalmol. 1998;116:1031-1035.
10. Smith W, Mitchell P, Leeder SR. Smoking and age-related maculopathy. The Blue Mountains Eye Study. Arch Ophthalmol. 1996;114:1518-1523.
11. Hankinson SE, Willett WC, Colditz GA, et al. A prospective study of cigarette smoking and risk of cataract surgery in women. JAMA. 1992;268:994-998.
12. Christen WG, Manson JE, Seddon JM, et al. A prospective study of cigarette smoking and risk of cataract in men. JAMA. 1992;268:989-993.
13. Macular Photocoagulation Study Group. Risk factors for choroidal neovascularization in the second eye of patients with juxtafoveal or subfoveal choroidal neovascularization secondary to age-related macular degeneration.. Arch Ophthalmol. 1997;115:741-747.
14. Klein R, Klein BE, Moss SE. Relation of smoking to the incidence of age-related maculopathy. The Beaver Dam Eye Study. Am J Epidemiol. 1998;147:103-110.
15. Klein R, Klein BE, Jensen SC, Meuer SM. The five-year incidence and progression of age-related maculopathy: the Beaver Dam Eye Study. Ophthalmology. 1997;104:7-21.
16. Mitchell P, Smith W, Wang JJ, Leeder SR. Smoking and the incidence of age-related maculopathy lesions: the Blue Mountains Eye Study. Invest Ophthalmol Vis Sci. 2000;41:S120 (Abstract 615).
17. Mitchell P, Chapman S, Smith W. "Smoking is a major cause of blindness": A new cigarette pack warning? Med J Aust. 1999;171:173-174.
18. McCarty CA, Keeffe JE, Livingston PM, Taylor HR. The importance and state of medical and public health research related to vision in Australia. Aust N Z J Ophthalmol. 1996;24:3-5.
Page currency, Latest update: 14 February, 2006