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Risk Factors for Macular Degeneration - An overview of current evidence

Eyes, Age related illnesses | August 2, 2014 | Author: The Super Pharmacist

Macular

Risk Factors for Macular Degeneration - An overview of current evidence

Macular degeneration, also known as age-related macular degeneration (AMD), is a serious eye condition that causes vision loss and sometimes blindness in a large percentage of elderly persons living in the United States. This disease affects a structure in the centre of the retina called the macula and there are two forms that are referred to as wet and dry. The wet form develops when abnormal blood vessels that leak blood and fluid, grow directly beneath the macula. The fluid buildup distorts the position of the macula and this reduces the ability to focus on images. Wet macular degeneration is the more aggressive form and vision loss generally develops in a short amount of time, but it only accounts for 10% of all diagnosed cases. The dry form develops when cells in the eye known as photoreceptors begin to deteriorate and fatty deposits called drusen begin to accumulate beneath the retina. Dry macular degeneration accounts for 90% of all diagnosed cases and is considered to be an early stage of the disease that is less aggressive.

What are the Risk Factors for Macular Degeneration?

Age

What are the Risk Factors for Macular Degeneration?Macular degeneration is the leading cause of vision loss and blindness in Australians who are 50 years of age and older. Furthermore, age is the main risk factor for developing this disease. More specifically, for individuals between the ages of 50 to 59, the risk of suffering from this condition is 2%, while this percentage increases to 30% for individuals who are 75 and older.

Racial Background

Race is also associated with the occurrence of macular degeneration as this disease develops in non-Hispanic Caucasian Americans more than non-Hispanic African Americans.

Gender

Women also tend to suffer from wet macular degeneration more often than men.

Genetics

In addition, people who have a family history of macular degeneration have a higher risk of developing this condition and this may be due to genetic variations in certain genes such as the complement factor h (CFH) gene. The CFH genes have several functions that include destroying harmful microorganisms (e.g. bacteria or viruses) and removing debris from bodily tissue and cells. Research indicates that genetic alterations of this gene, which may be inherited, increase the susceptibility of developing macular degeneration and this appears to be irrespective of race.

Lifestyle Factors

Lifestyle is another important factor that plays a role in the development of this disease.

What are the Risk Factors for Macular Degeneration?Diet - In particular, people who have a diet that is not rich in fish and green, leafy vegetables have a high risk of developing macular degeneration. These types of foods contain essential vitamins and minerals such as omega-3 fatty acids, beta-carotene, lutein, and zeaxanthin, which have all been scientifically demonstrated to prevent the occurrence of macular degeneration in older persons and slow the progression of vision loss in those who have the disease.

Due to the current statistics regarding the incident rate of macular degeneration in the elderly population, physicians now recommend that individuals 50 years of age and older take a daily supplement containing the above nutrients in addition to maintaining a proper diet. According to the National Eye Institute, over 14,000 macular degeneration events (e.g. blurred vision and vision loss) can be avoided annually if all adults in the United States who are diagnosed with this condition took amounts of dietary vitamins that have been found through research to prevent the progression of this disease.

Weight - Being obese and having an elevated level of high-density lipoprotein (HDL) cholesterol (good cholesterol) has been linked to the onset of macular degeneration as well. High HDL cholesterol, in particular, is associated with the late stage of the dry form. A diet that is high in fat and cholesterol content can cause fatty deposits to buildup in macular vessels and this results in reduced blood flow to the eyes.

Smoking - Smoking cigarettes is another significant factor that plays a role in the incidence and progression of macular degeneration.

What are the Risk Factors for Macular Degeneration?Long-term research that was conducted over a 20-year period showed that smoking can quicken the progression of this disease from a mild to moderate stage and cause a two-fold increase in its occurrence.

Accordingly, as the number of pack-years smoked increases so did the risk of transitioning from no macular degeneration to an early stage of the disease or from a moderate to severe stage.

Furthermore, the incidence of early (dry) macular degeneration in smokers was higher than the incidence of the late (wet) form in the observed population.

The tar that is contained in cigarettes and the smoke that is produced, lead to the thickening of the retina as well as the formation of fatty deposits underneath the surface. More specifically, the oxidants in cigarettes are believed to elicit changes in the retina that result in macular degeneration, especially the dry form. Therefore, smoking is a particularly harmful risk factor.

Environmental Factors

In addition to having an improper diet or being genetically predisposed to developing this disease, certain environmental factors also appear to contribute to the progression of macular degeneration. For instance, when people are exposed to lead and cadmium, these substances can accumulate in the retina and begin to cause damage due to inflammation and oxidative stress that may lead to the development of this condition. Moreover, there is stronger association between cadmium exposure and macular degeneration in non-Hispanic Caucasian Americans than in non-Hispanic African Americans.

Summary

Age is the main risk factor that is associated with the occurrence of macular degeneration with an incidence rate that dramatically increases in individuals who are 50 years of age and older.

Smoking is a risk factor that is strongly associated with an increased incidence of macular degeneration.

Additional factors such as a family history, a diet that is low in fish and green, leafy vegetables or high in fat and cholesterol, and even environmental exposure to harmful substances such as lead and cadmium are also associated with the development and progression of this disease.

As research continues to reveal factors that contribute to this common eye condition, the ability to prevent and successfully treat macular degeneration will undoubtedly improve.

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References

National Eye Institute (2009). Age-related macular degeneration: What you should know. The National Eye Institute's Office of Science Communications: Bethesda, MD. Retrieved from http://www.eyeresearch.org/pdf/nei_wysk_amd.pdf

Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol, 2001; 119(10):1417-1436.

Mitchell P,Wang J, Foran S, et al. Five-year incidence of age-related maculopathy lesions: The Blue Mountains Eye Study. Ophthalmol, 2002; 109:1092-1097.

Wu EW, Schaumberg DA, Park SK. (2014). Environmental cadmium and lead exposures and age-related macular degeneration in U.S. adults: The National Health and Nutrition Examination Survey 2005 to 2008. Environ Res, 133C:178-184.

Myers CE, Klein BE, Gangnon R, Sivakumaran TA, Iyengar SK, Klein R. (2014). Cigarette smoking and the natural history of age-related macular degeneration: The Beaver Dam Eye Study. Ophthalmol, in press.

Jonasson F, Fisher DE, Eiriksdottir G, Sigurdsson S, Klein R, Launer LJ, Harris T, Gudnason V, Cotch MF. (2014). Five-Year Incidence, Progression, and Risk Factors for Age-related Macular Degeneration: The Age, Gene/Environment Susceptibility Study. Ophthalmol, in press.

Wang X, Geng P, Zhang Y, Zhang M. (2014). Association between complement factor H Val62Ile polymorphism and age-related macular degeneration susceptibility: A meta-analysis. Gene, 538(2):306-312.

Chew EY, Clemons TE, Agrón E, Sperduto RD, Sangiovanni JP, Kurinij N, Davis MD, Age-Related Eye Disease Study Research Group. Long-term effects of vitamins C and E, β-carotene, and zinc on age-related macular degeneration: AREDS report no. 35. Ophthalmol. 2013; 120(8):1604-1611.

Espinosa-Heidmann DG, Suner IJ, Catanuto P, Hernandez EP, Marin-Castano ME, Cousins SW. (2006). Cigarette smoke-related oxidants and the development of sub-RPE deposits in an experimental animal model of dry AMD. Invest Ophthalmol Vis Sci, 47(2):729-737.

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