DRY AMD AND WET AMD
As noted earlier, AMD is classified into two general types: dry AMD (also known as atrophic or non-neovascular) and wet AMD (also known as exudative or neovascular). Dry AMD is the more prevalent type, accounting for about 90 percent of AMD cases, while the remaining 10 percent of cases are wet.22 Wet AMD, however, is the more rapidly progressive type and a more frequent cause of severe visual loss. 23
Each type of AMD affects the vision in a different way, but peripheral vision is rarely affected. Dry AMD may cause little or no visual symptoms at its initial onset, while a common early symptom of wet AMD is a sudden blurring in vision or seeing straight lines as wavy.
What Is Dry AMD?
Dry AMD occurs when the layer of cells beneath the retina, the retinal pigment epithelium, begins to deteriorate. This, in turn, affects the overlying retina, particularly the light-sensitive cone cells (responsible for central vision and color perception), gradually dulling and blurring central vision in the affected eye. Dry AMD tends to progress over a matter of years, more slowly than wet AMD. As dry AMD gets worse, a person may see a blurred or blank spot in the center of vision or notice a gradual decline in his/her ability to see fine print or detail in images. Gradually, as less of the macula functions, central vision in the affected eye may be lost. In some individuals, as dry AMD worsens, new blood vessels may begin to grow, and the condition can progress into wet AMD.24
The most common symptom of dry AMD is gradual blurring of vision. People with dry AMD may have difficulty recognizing faces or may need more light for reading and other tasks. Dry AMD generally affects both eyes, but vision can be lost in one eye while the other eye seems unaffected. In fact, vision loss from dry or wet AMD in one eye may not result in noticeable changes in overall vision. People can still drive, read and see fine details with the eye that still sees clearly. A Science Writers’
One of the most common early signs of dry AMD is drusen, which are yellow-white deposits that accumulate under the retina. The presence of drusen may result in a reduction in function and thinning of macular tissues and gradual vision loss that occurs over years. A harmless type of drusen is often found in people over age 60, and almost all people over the age of 50 have at least one small druse in one or both eyes.25 Ophthalmologists can detect and differentiate among types of drusen during a comprehensive dilated eye exam.
Dry AMD has three stages, all of which may occur in one or both eyes:
Early AMD – People with early AMD have either several small drusen or a few medium-sized drusen. At this stage, there are usually no symptoms and no vision loss although there may be loss of contrast sensitivity. People without contrast sensitivity, for example, may have trouble seeing the screen of an ATM machine or a menu in a dark restaurant.
Intermediate AMD – People with intermediate AMD have either many medium-sized drusen or one or more large drusen. Some people see a blurred spot in the center of their vision. More light and some magnification may be needed for reading and other tasks.
Advanced Dry AMD – In addition to drusen, people with advanced dry AMD have localized loss of the retinal pigment epithelium under the retina, resulting in a loss in function of the overlying photoreceptors (cones) in the central retinal area. This breakdown can cause a blurred or blank spot in the center of a person’s vision. Over time, the blurred spot may get bigger and darker, with increasing vision loss. This stage is referred to as geographic atrophy.
People with early dry AMD have a 1.3 percent risk of developing advanced AMD over any given five-year period. Those with intermediate dry AMD have an 18 percent chance of progressing to advanced dry AMD or wet AMD.26
What Is Wet AMD?
Wet AMD occurs when abnormal blood vessels begin to grow under the macula. These new blood vessels leak fluid or blood, resulting in loss of retinal function. Once the fluid or blood begins to accumulate in the macula, photoreceptor cells degenerate and die. Damage to the macula occurs rapidly, sometimes within months, resulting in blurred or even lost central vision.27
Recent clinical studies suggest that there may be some value in classifying wet AMD into different subtypes based on the appearance of these abnormal blood vessels as imaged with a procedure known as fluorescein angiography (see below). This classification may be useful in understanding the natural course of the condition and response to treatment in patients with wet AMD. The classifications are: predominantly classic, minimally classic, and occult.
Predominantly Classic – This subtype has the most aggressive disease pathology and accounts for approximately 25 percent of wet AMD cases. Studies suggest that this subtype leads to more rapid vision loss than the other subtypes.28, 29, 30 Lesions in the classic forms are well defined. 31
Minimally Classic – This subtype has a less rapid rate of vision loss than the predominantly classic subtype, and together with the occult subtype, accounts for the remaining 75 percent of wet AMD cases.
Occult – In the occult subtype a patient’s lesions are not well defined, and they have less leakage than the classic subtypes.32 This subtype generally has a less rapid rate of vision loss than predominantly classic, and together with the minimally classic subtype, accounts for approximately 75 percent of wet AMD cases.
An early symptom of wet AMD is blurred central vision and/or awareness that straight lines appear wavy. People who notice these symptoms or other changes are encouraged to contact an ophthalmologist promptly for a comprehensive dilated eye exam. Once afflicted, people with wet AMD also tend to see a dark spot or spots as a result of the blood or fluid under the macula.
Additionally, about 43 percent of people with wet AMD in one eye progress to wet AMD in both eyes within five years.33 Since both forms of AMD can progress, it is important that patients continue visiting their ophthalmologists, remain aware of changes in vision and seek immediate medical care at the first signs of any changes.
