Age-Related Macular Degeneration (AMD) is a deterioration of the macula, the central area of the retina, that can cause substantial central visual loss but almost never total blindness. AMD is the leading cause of significant visual acuity loss in seniors and dramatically increases with age. There are 2 types of AMD: non-neovascular or dry AMD; and neovascular or wet AMD.
The retina is a thin layer of light-sensitive nerve tissue lining the inner wall of the eye. When light is focused onto the retina, the images are converted into electrical signals that are carried from the eye to the brain by the trunk line of the optic nerve. The visual portion of the brain interprets these as images. The macula is the specialized portion of the central retina packed with cone photoreceptors and is the only part of the retina capable of fine vision and reading. Imaging can visualize most of the layers of the retina that are only a few hundred microns thick in the center.
Symptoms
The macula is responsible for the fine central vision for tasks such as reading small print and is subject to over 50 other conditions. In the early stages, AMD (and other macular problems) may have no symptoms at all. The dry type of macular degeneration usually progresses very slowly with fewer symptoms that slowly progress over a period of a decade. The wet type can progress suddenly with distortion and progressive central visual loss that, without treatment, usually causes loss of most of the central vision within 6 months or a year at most. Macular degeneration symptoms include:
● Distortion (warping) of straight lines, such as a Venetian blind.
● Faded colors.
● Loss of central vision with difficulty reading and seeing faces.
● Dark, blurry areas in the center of vision.
Risk Factors
● Age—the strongest risk factor.● Family history of AMD.● Caucasian race.● Cigarette smoking.● Female gender.● High blood pressure.● Higher level of education.● High cholesterol.● Light iris color.● Sunlight exposure.● Far-sightedness.● Low dietary fish intake.● Cardiovascular (heart) disease.● Use of more than 2 full aspirins daily.
Diagnostic Testing
When symptoms or exam findings are noted on clinical exam, additional testing may be performed, including imaging to determine the presence or absence of a leak or an abnormal blood vessel or to identify other causes of the macular disease. Disease features related to AMD may be found in the retina and in the layers beneath it. According to these abnormal findings, AMD is classified as dry or wet.
An AMD diagnosis is confirmed with specialized imaging, including:
● Optical coherence tomography (OCT). This non-invasive imaging technique uses low-power laser light to create a 3-dimensional image of your retina that shows leakage within or under the retina.
● Fundus autofluoresce. This imaging technique uses a blue light to illuminate the retina. Special filters allow the reflected light to be captured often identifying areas of dry macular degeneration
● Fluorescein angiography (FA). This imaging technique utilizes a teaspoon of a yellow vegetable dye called fluorescein that is injected into a vein in the arm. A low-power laser imaging instrument records the circulation in the retina and choroid in the back of the eye. The dye is excreted rapidly in the urine and can be used in most patients with renal disease. This test can be very useful in diagnosing a number of retinal disorders.
● Indocyanine green angiography (ICG). This diagnostic procedure uses a green dye to illuminate blood flow in the choroid, which is a layer of blood vessels located under the retina where the abnormal neovascular membranes usually originate.
Other tests helpful for evaluating both dry and wet AMD include:
● Color photographs to document the number and location of drusen, the presence or absence of pigment, blood, or discoloration, and the extent of the area involved. The digital pictures are useful for following the disease for progression and response to treatment.
● Visual fields. Blind spots near the center of the vision may be identified with testing of the central visual field. These defects may cause problems with reading even when the vision is 20/20.
● Color vision may be affected by macular degeneration.
Dry AMD usually starts with discolored yellowish spots on the retina, called drusen analogous to blotchy skin. Dry AMD typically slowly progresses over years with pigment changes and then progress to a confluent spot of pigment loss called geographic atrophy (GA) with a missing, or central blind spot.
Drusen precursors of Dry AMD.
Intermediate dry AMD with more drusen and pigmentary change in the central macula.
In contrast, wet (exudative or neovascular) AMD involves fluid or blood leaking from an abnormal blood vessel that grows from the choroid layer of blood vessels under the retina. As it progresses, it leaks under or within the retina causing thicken. Subsequently, the abnormal choroidal neovascular membrane bleeds and then scar tissue forms with irreversible loss of central vision.
Early Wet AMD. Choroidal neovascularization.
Advanced Wet AMD with Disciform scar.
EyeSmart - American Academy of Ophthalmology
An Amsler grid is an excellent tool for monitoring the macula. The test is performed one eye at a time with glasses used for reading. Symptoms of a macular problem are noted in about 90% of cases but not always.