Age-Related Macular Degeneration (AMD) is the leading cause of blindness in people over the age of 50 in developed countries, affecting more than 30 million people worldwide. It is characterized by the loss of central vision due to the gradual deterioration the macula—the part of the eye that allows you to see fine details and where sharp central vision occurs. AMD makes precious daily activities, such as reading, driving, recognizing faces, watching television, and navigating stairs, difficult.
AMD does not cause pain and its progression varies, advancing slowly or quickly, in one eye or both eyes. When AMD develops with a very gradual decline in vision, the brain can initially compensate, and its symptoms may not be easily noticed. When the disease advances rapidly, it may swiftly lead to discernible vision loss. Regardless of how quickly the disease progresses, if left untreated, advanced AMD may lead to permanent loss of vision.
AMD has two forms: Wet and Dry.
Dry AMD is the most common form of AMD, with early or intermediate stages accounting for approximately 90% of all cases. In these earlier stages of Dry AMD, there is a decline in function of the macula, associated with the accumulation of drusen—yellow deposits in the back of the eye that can vary in size and number, considered part of the normal aging of the eye. In early stage Dry AMD, people have multiple smaller drusen or a few medium-sized drusen, with no vision loss. Early stage Dry AMD can develop into intermediate Dry AMD, as more small drusen or one or more large drusen develop. Symptoms that arise during intermediate stage Dry AMD include wavy or blurred spots in the center of vision, and difficulty reading.
Intermediate Dry AMD can develop into advanced Dry AMD or wet AMD. In advanced Dry AMD, the progressive increase in the number and/or size of drusen is accompanied by the deterioration of the light-sensing cells and surrounding tissue in the macula, which is called “geographic atrophy”. Geographic atrophy causes more significant and irreversible vision problems, such as a larger, darker spot in the center of vision, decreased contrast sensitivity, difficulty adjusting from bright to dim lighting, and challenges in reading small print.
One eye or both eyes may be affected by Dry AMD. When only one eye is affected, vision loss is harder to detect because the “good eye” works harder to make up for the deficiency in the affected eye. That’s why it’s important to have regular eye exams to keep tabs on visual acuity in both eyes.
Wet AMD is the most serious and severe form of AMD and occurs only as an advanced stage of disease. While all people who develop wet AMD have Dry AMD first, only 10 to 15% of people with Dry AMD progress to the Wet form. Also referred to as “exudative macular degeneration”, wet AMD is characterized by growth and leaking of abnormal blood vessels under the macula.
Unlike Dry AMD, which develops slowly and in stages, wet AMD can rapidly damage the macula and quickly cause a loss of central vision. That’s why periodic eye examinations are very important for patients at high risk of wet AMD.
In wet AMD, blood vessels grow abnormally beneath the macula, through a process called angiogenesis. These abnormal vessels leak fluid and blood, which may cause a blister-like pocket to form beneath the macula. These blisters distort vision in the affected eye, making straight lines appear wavy. The patient may see a dark spot or various spots in the center of their vision. This is due to blood or fluid collecting under the macula.
If wet AMD is left untreated, bleeding in the eye can cause scar tissue to form, leading to irreversible vision loss. The good news is that there are several effective treatment options for wet AMD. These treatments can stabilize or, in some cases, even reverse vision loss, if used before scar tissue forms.
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