Age-Related Macular Degeneration
Age-related macular degeneration (AMD) is a chronic retinal disease characterized by progressive and often irreversible loss of central vision. AMD is the leading cause of blindness in the U.S. and other industrialized countries. It has an estimated global prevalence of 8.7% and the number of people with the disease worldwide is projected to increase from 196 million in 2020 to 288 million in 2040 due to anticipated growth in the number of elderly people in the population. In the U.S., an estimated 10 million people have AMD, which is comparable in scope to the number of people with cancer (12 million) or Alzheimer’s disease (5 million).
There are two forms of AMD: dry (atrophic) and wet (neovascular or exudative). Most AMD starts as the dry type but in 10–20% of individuals, it progresses to the wet type. It is possible to have the wet type in one eye and the dry type in the other. The dry form affects approximately 80–90% of individuals with AMD. It tends to progress more slowly than the wet type, and there is not yet an approved treatment.
The wet/neovascular type affects approximately 10-15% of individuals with age-related macular degeneration, but accounts for as much as 90% of all cases of severe vision loss from the disease. In wet age-related macular degeneration, abnormal blood vessels under the retina begin to grow toward the macula. This process is known as choroidal neovascularization (CNV). Because these new blood vessels are abnormal, they tend to break, bleed, and leak fluid into the retina and subretinal space, which can result in swelling, damage to the macula as a result of serous or hemorrhagic retinal detachment, and fibrovascular scar formation. This can result in rapid and severe loss of central vision.
Wet AMD is the most common form of central vision loss in those over 55 years of age and is the third-leading cause of blindness worldwide. It is associated with a significant burden both in economic impact and the quality of life of patients. Visual impairment associated with wet AMD can lead to significant functional loss, reduced health-related quality of life, and depression.
Existing treatments for wet AMD include photodynamic therapy and intravitreal injection of anti-VEGF agents; however the effectiveness of these therapies remains limited. Anti-VEGF therapy may improve visual acuity but most patients do not achieve significant visual gain over time and many continue to lose vision. In addition, anti-VEGF therapy requires frequent treatment, which poses a burden with respect to compliance. Undertreatment and underdosing are common with anti-VEGF agents, and there are unresolved concerns regarding the safety of long-term use.