What Causes Dry Macular Degeneration

hazy visionDry Age-Related Macular Degeneration (AMD) is caused when the central part of the retina, the macula, deteriorates. The macula is responsible for detailed and colour vision, and is a highly specialized part of the eye. The photoreceptors in the macula that react to light stimulus, and the neurons that interpret and transmit the signals, are precisely organized. This vision is necessary for tasks such as recognizing faces, and reading.
 
Dry, or atrophic AMD happens when cells in the macula break down. As the disease progresses, central vision becomes blurred. The classic lesion is geographic atrophy – a discrete area of retinal depigmentation with sharp borders and visible choroidal vessels.
 
The precursor to AMD is the proliferation of drusen – tiny yellow or white accumulations of extracellular material in the eye. These may be present without causing vision loss, but when they grow larger, more numerous, or become soft, AMD is usually present. In addition, if there are changes in the pigment, chances of developing either wet or dry AMD are greatly increased.
 

Risk Factors

 
The reasons for retinal deterioration are not entirely clear, but the onset of dry AMD appears to be due to a combination of factors.
  • Heredity. Not least of these risk factors is family history. Patients with first-degree relatives who developed severe AMD have a four times greater chance of developing the disease themselves.
  • Complement Factor H Gene. This gene mutation is thought to be responsible for half the cases of AMD in North America. People with a CFH gene variant have a 2.5 – 5 times greater likelihood of developing AMD.
  • Age. The most common risk factor is age. Patients 65 – 74 years of age have a 10% risk of developing AMD; between the ages of 75 – 84, that risk increases to 30%.
  • Smoking. A modifiable risk factor is smoking. The risk of current smokers developing AMD is two to three-fold higher than the risk of people who have never smoked. Quitting smoking lowers one’s risk.
  • Drusen. Examination shows that drusen are similar in molecular composition to plaques found in Alzheimer’s or atherosclerosis. However, it is possible to have drusen without vision loss, which suggests that at least one other factor must be in play.
  • Obesity. A BMI of 30 or more increases a person’s risk of developing advanced AMD by 2.5.
  • Diet. High fat intake increases risk of cardiovascular disease, high cholesterol and AMD. North American diets often include a high percentage of animal fat and dairy fat.
  • Gender. The disease occurs more often in women than in men.
  • Race. Non-Hispanic whites are most susceptible to AMD.
  • Oxidative Stress. Some researchers contend that phototoxic free radicals in the retinal pigment epithelium may be at least partly responsible for AMD.
  • Exposure to sunlight. It is thought that prolonged exposure to sunlight (particularly blue light) over a number of years may increase incidence of AMD.

Conclusion

While the exact causes of AMD are not clear, several risk factors have been identified. Supplementation with antioxidants and carotenoids can help to ameliorate the effects of dry AMD.

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