Age-related macular degeneration is a common eye condition and also a leading cause of vision loss among those 50 and older. The condition causes damage to the macula, a small spot near the center of the retina, which is the area of the eye needed for sharp, central vision.
One marked similarity between AMD and Alzheimer's disease is that the most common risk for developing them is age, so they are both age-related.
Additionally, both conditions affect thousands of people worldwide. According to the National Eye Institute, there are about 11 million people who have some form of AMD in the U.S. and the number is expected to grow to 22 million by the year 2020. Further, AMD is expensive to treat, with an estimated cost of $512 billion in 2016, as reported by the institute.
Alzheimer's disease ranks second behind AMD as an aging disorder that causes a high degree of damage. Currently, according to reports from the Alzheimer's Association, there are 5.4 million people with the disease. These numbers are projected to increase to approximately 13.8 million by 2050. Alzheimer's care also is costly, with the cost in 2016 reported as $236 billion.
Similarly, both AMD and Alzheimer's disease are found more frequently in women than in men, and approximately 5-15 percent of cases are found in more than one family member.
Additionally, there remains a genetic risk factor in both diseases. The lipid transport protein called Apolipoprotein E that provides an elevated risk to people for AMD if they carry the allele-2 variant and a higher risk for Alzheimer's in people if they carry the allele-4 variant.
Furthermore, there are three events that make pathologies similar in both diseases, with the exception that they are found in different locations — either the retina or the brain.
The first similar pathology is the amyloid beta protein, which accumulates in large quantities identified in the brain of an individual with Alzheimer's, and the presence of these plaques is defining in the disease. With those diagnosed with AMD, amyloid-beta deposits also are found and accumulate underneath the retina and eventually form small clumps of protein-lipid materials call drusen. The accumulation of the amyloid protein causes eventual widespread cell death in both diseases.
The second similar pathological feature in AMD and Alzheimer's is there are high levels of tissue damage and loss of cell function, with cell death occurring in the retina and the brain.
The third pathological similarity is damage to the mitochondria, which are small units within the cell that remain critical in keeping the cell alive. The mitochondria work like batteries in that they provide energy to keep the retina and brain cells functioning. When the mitochondria begin to lose this energy and die, the cells lose their function, and eventually cell death occurs. Mitochondria are critical in the function of cells and in keeping them alive, and this is true for all types of cells in our bodies, including nerve cells, muscle cells, retina cells, heart cells, etc.
While research has determined that there is no association between having AMD and then developing Alzheimer's or dementia, the diseases share common risk factors in addition to aging, such as high blood pressure, high cholesterol and cigarette smoking.