AMD is the leading cause of vision loss in developed countries, and accounts for 8.7% of visual impairment worldwide. AMD is caused by a combination of genetic and environmental factors with age being the greatest risk factor. In the United States, AMD affects 7 percent of people age 60-69 and 35 percent of people age 80 and older (National Institutes of Health). AMD occurs in two forms: dry (nonexudative) and wet (exudative or neovascular). Ninety percent of all people with AMD have the dry type, which includes the early and intermediate stages of AMD, as well as the advanced form known as geographic atrophy. The wet form affects 10 percent of all people with AMD, and accounts for 90 percent of legal blindness from the disease.
Estimating Risk of AMD Progression
The Age-Related Eye Disease Study (AREDS) 9-step severity scale and the simplified 5-step severity scale use drusen size and pigmentary abnormalities to determine a risk score upon clinical examination.
|AREDS Risk Factor Scoring Systemb|
|+1 For each eye with large drusen|
|+1 For each eye with pigment abnormalities|
|+1 If neither eye has large drusen, but both eyes have intermediate drusen|
|+2 For the eye that has neovascular AMD
Small: <63 μm
Intermediate (black arrow): 63-124 μm
Large (green arrow): 125*-249 μm
Very Large (blue arrow): >250 μm
* 125 μm is roughly the width of a retinal vein
where it crosses the optic disc.
AREDS Simplified Severity Scaleb
|5-year rates of progression to advanced AMD||0.5%||3%||12%||25%||50%|
aAdapted from Age-Related Eye Disease Study report no. 17 bAdapted from Age-Related Eye Disease Study report no. 18