The diagnosis of macular degeneration is becoming increasingly more common due to patient awareness, physician access, and the relentless graying of the population exponentially increasing the percentage of the population at risk for this condition. Thus, macular degeneration is a formidable challenge to patients, their doctors, and our society as the costs for delivering state-of-the-art care increases secondary to groundbreaking improvements in treatment.
Macular degeneration, also called age-related macular degeneration (AMD or ARMD) or the now discarded term, senile macular degeneration (SMD), describes a variety of pathologic but extremely common conditions that affect the macula, the central portion of the retina responsible for detailed vision and color vision, the vision we use to read, thread a needle, sign a check, or recognize faces. It is the macula that allows humans to see 20/20, or an eagle to spot a small rodent on the ground hundreds of feet below. The retina is the nerve tissue lining the inside wall of the back of the eye consisting of the receptors and nerves that collect and transmit light signals from the eye into the optic nerve, then to the brain for interpretation as our sense of vision. The retina, other than the central macula, is responsible for peripheral vision but not sharp acuity.
Age-related macular degeneration is the leading cause of legal blindness in people older than 55 years in the United States. Age-related macular degeneration affects more than 1.75 million individuals in the United States. Owing to the rapid aging of the U.S. population, this number is expected to increase to almost 3 million by 2020. Because overall life expectancy continues to increase, age-related macular degeneration has become a major public-health concern.
There are two types of age-related macular degeneration:
Atrophic: This type of dry macular degeneration results from the gradual breakdown of cells in the macula, resulting in a gradual blurring of central vision. Single or multiple, small, round, yellow-white spots called drusen are the key identifiers for the dry type. These spots are located in the back of the eye at the level of the outer retina and are detected by examination of the retina with specifically engineered lenses, a slit-lamp biomicroscope, or an ophthalmoscope. Spots typically become visible when a person reaches his or her late 30s or older but are much more common in people over the age of 70. People with these spots may have excellent vision and no symptoms. Most people with age-related macular degeneration begin with the dry form. The dry form of macular degeneration is fortunately much more common than the wet form. Advanced dry macular degeneration, known as geographic atrophy, is the culmination of prolonged, progressive wasting changes in the nerves and sensory retina. Geographic atrophy is the main cause of vision loss in dry AMD, not drusen. There is no known treatment for atrophic dry macula degeneration, although vitamins have some benefit in slowing the progression.
Non-atrophic: This consists mostly of two entities that can sometimes benefit from surgical intervention called vitrectomy surgery. The first is caused by fibrotic tissue developing on the surface of the retina, called an "epiretinal membrane or cellophane maculopathy." The second is caused by the formation of a hole in the central retina called a "macula hole".
Wet (exudative or neovascular) form
In the wet form of macular degeneration, newly created abnormal blood vessels grow under the center of the retina. These blood vessels leak, bleed, and scar the retina, distorting or destroying central vision. Vision distortion usually starts in one eye and may affect the other eye later. In contrast to the dry type, vision loss may be rapid in the wet type of macular degeneration. Treatment consists either of light energy to burn the vessels closed (laser therapy) or more recently of intraocular injection of endothelial growth factor inhibitors such as Lucentis (ranibizumab) or Avastin (bevacizumab).