Age-related macular degeneration, commonly known as macular degeneration or AMD, is the No. 1 cause of central vision loss in people over 50 years old. (Diabetes is the No. 1 cause of vision loss in younger people.) The condition impairs central vision – the sight in the center of a person's visual world – causing a disturbance that can range from mild blurring and distortion to a “dark blob” or blank or blind spot. A person's peripheral vision is generally left entirely intact by macular degeneration.
Figure 1: Illustrates a Blind Spot
Figure 2: Normal Vision
The macula is a tiny area of the retina about 3mm in diameter in the back of the eye. It is the only part capable of providing fine vision, for detailed tasks such as reading and distinguishing subtle features. Changes of normal macular aging become visible as years pass, during a regular dilated eye examination, and some of these changes might presage macular degeneration. However it is important not to assign the diagnosis of macular degeneration when the only evident findings are those of the normal aging eye.
Macular degeneration is clinically divided into two overlapping types that are linked by their location in the back of the eye and, increasingly, by genetic research being performed all over the world.
Atrophic or “dry” AMD composes about 85 percent of all macular degeneration cases, according to the National Eye Institute. As with most age-related anatomical changes, this type has a very gradual onset. Its effects usually are mild, almost imperceptible at onset. Most people with this type relate that they need stronger glasses or bifocals, or need more light to see adequately.
Neovascular or “wet” AMDcomposes the remainder of macular degeneration cases. Although it is the minority, this type’s effects are more debilitating and may have an abrupt onset; patients might experience vision that seems distorted compared with only days or weeks earlier. The person frequently sees straight lines as wavy, and/or experience blank spots and decreased central vision of fairly recent onset.
AMD affects both eyes, though one eye might change earlier than the other. Some people might not notice the effect in one eye (usually the non-dominant eye) because lack of function is not apparent when both eyes are open. Our brain’s flexibility helps mask AMD, and for this reason, a delayed diagnosis is not rare.
The dry type also might be complicated by the development of the wet type but this is not common. Everyone who has wet macular degeneration can be thought of as having some degree of the more common dry AMD.
Patients commonly realize they have a disturbance of vision in one eye, or are not seeing very well, so they call an optometrist or ophthalmologists. Ophthalmologists are best trained to examine the eye to determine whether macular degeneration exists, and are the only eye-care providers who can provide accurate advice and, if needed, treatment.
In suspected cases of macular degeneration, and particularly when a patient notices abrupt vision change, rapid evaluation and possible intervention is important to give the patient the best chance to optimal management. People who are 50 to 60 or older and have no symptoms but have relatives with macular degeneration should advise their ophthalmologist, who can provide counsel about nutritional supplements and ways to monitor vision.
Potentially useful are dietary changes, smoking cessation, medicinal therapy and surgery (laser approaches, injections and others). Improvements vary from dramatic to mild among patients, determined by the nature of the disease, genetics and other still to-be-discovered factors.
Macular generation does not cause pain, eye redness or other symptoms unrelated to sight. Patients commonly realize they have a disturbance of vision in one eye or are not seeing normally, despite the use of glasses or contact lenses.
Dry macular degeneration emerges slowly, with subtle symptoms. Most people with this type sense that they need stronger glasses or bifocals, or need more light to see adequately, but not with a sudden onset. Patients might experience blurring in the center of their vision; some patients might notice small, empty areas of vision (e.g., a person could miss one side of words while s/he reads.)
The dry condition usually affects both eyes, but some might note this in only one eye. Patients often have delayed awareness of vision symptoms in their non-dominant eye. Symptoms are strictly sight-related.
With wet macular generation, patients’ vision might seem distorted compared with only a few days or a week earlier. The person might see straight lines as wavy, and/or experience blank spots and decreased central vision fairly suddenly.
Macular degeneration stems from factors that differ among individuals. The most prominent and recognized causes are age and genetics.
With dry macular degeneration, the retina’s layers in the macula appear to thin on their own. The retina has 10 layers of tissues under the microscope, and ophthalmologists can recognize certain of these layers growing thinner, somewhat as the heel of a sock would thin with wear. To be clear, though, the development of dry macular degeneration is not due to use of the eyes, so limiting reading or other activities does not prevent or stop macular degeneration.
Wet macular degeneration occurs when blood vessels behind the retina grow abnormally into the space beneath the macula. The cellular barrier that normally keeps these vessels in their place is breached. Blood and other nutritional fluids carried by the vessels leak beneath the macular retinal cells. Under the normally flat retinal tissues, the vessels and fluid act much as ripples under a carpet, creating distortion of vision and reducing acuity in the central retina.
Recently we have come to understand that the vessels' growth is associated with the body's production of vascular endothilial growth factor (VEGF) – proteins that help create and regulate blood vessels throughout the human circulatory system.
The dry type rarely transforms into the wet type; however, virtually everyone who has wet macular degeneration had the dry type first. A person could develop dry AMD in one eye and wet in the other.
Aging, in every tissue, there is a microscopic battle between stresses on cells and the cells' ability to withstand those stresses. In the cells of the retina's layers, stresses may slowly weaken those structures to the point of dry macular degeneration; similarly the barrier cells that typically keep blood vessels from growing may break down, initiating wet degeneration. Again, it is not overuse that contributes to the cells' wear, but aging and other factors.
The vast majority of people will show aging retinal signs developing progressively throughout their lifespan (mostly in their 60s and beyond) and never develop macular degeneration.
Age: Age is the greatest risk factor. Macular degeneration can emerge during middle age, but people over age 60 are at greater risk than other age groups.
Race and ethnicity: People with lighter eye color and skin pigmentation are at greatest risk: Among populations, blue-eyed Caucasians are much more likely to develop the condition than African-Americans, Asians, Hispanics and other more pigmented races.
Gender: Women generally appear to be at slightly higher risk than men.
Genetics: A family history of macular degeneration raises the likelihood of developing the disease.
Lifestyle: Smoking and obesity may increase one’s risk for macular degeneration. Data suggests that a diet heavy in leafy green vegetables correlates with a lower likelihood of developing macular degeneration.
Environment: Lifelong significant exposure to light also has been suggested as a risk factor, but substantial supporting data is incomplete.
With many age-related diseases, it can be difficult to differentiate early disease from normal aging. Dry macular degeneration’s slow onset is very different from that of a broken bone, for example, whose anatomic change is revealed in an instant. Normal aging changes are visible during a dilated eye examination, and some of those changes might be precursors to macular degeneration.
Macular degeneration correlates with the presence of drusen – tiny yellow or white deposits in the back of eyes (beneath the retina) of older people, particularly in lighter-pigmented races such as Caucasians. Drusen develop gradually, like age spots, and do not diminish eyesight, per se, but most people who develop macular degeneration have drusen, so their presence is important. However many more people have drusen than will develop macular degeneration. When ophthalmologists see drusen during otherwise normal exams of older patients, their presence suggests that the patient should be screened in the future for macular degeneration and given tips about how to monitor their vision for signs of macular degeneration.
Patients might anticipate the following examination steps, relevant to evaluation for AMD:
The Amsler grid
- visual acuity testing (best corrected with glasses or refracted with lenses in the clinic)
- Amsler grid testing, which a person can do for home screening
- dilated examination (in which drops dilate the pupil and enable the ophthalmologist to see the retina and optic nerve)
- special testing such as fluorescein angiography and optical coherence tomography (OCT)
) is a helpful mechanism for screening of central vision. Patients are asked to stare at the center dot, and if lines are missing or appear wavy, this may be suggestive of macular degeneration.
After pupil dilation, examination with a biomicroscope or “slit lamp” can reveal evidence of abnormal blood vessels, blood and/or fluid leakage under and around the macula.
Ophthalmologists also can perform a fluorescein angiogram, in which a fluid dye is injected into an arm vein to help reveal new blood vessels. Special camera equipment photographs the dye’s progression into the eye. These photographs help determine the blood vessels' location, size and activity, and help ophthalmologists supply appropriate information to patients about their options.
OCT gives a virtual “slice” of the contours of the central retina, in high magnification, using special a light (not radiation). This fairly recently developed test helps ophthalmologists assess microscopic evidence of conditions like AMD and many others.
Natural History of AMD
If dry macular degeneration is present, a person typically experiences a very slow loss of the fine features of vision such as a subtle decline in sense of contrast of vision and slower adaptation when moving from bright light situations. Blind spots in or near one’s central vision may gradually develop, making reading and other close-range tasks challenging. The average worst vision in dry AMD is fully adequate for most “life functions” such as caring for oneself and walking independently.
With wet AMD, the time course and severity of potential vision loss is accelerated. Early diagnosis is key to the best options and outcomes. This is due to the gradual growth of sub-retinal blood vessels and their tendency to eventually cause scarring and loss of retinal function in the affected area.
Legal blindness is defined as the level of vision loss equal to a person seeing the large E (20/400 vision level) and one smaller (20/200) as the best that person can see, even with glasses. An eye cannot be legally blind, only a person can be.
: People for whom medical, laser or other formal treatment by an ophthalmologist would have little value, a variety of specialized glasses, magnifiers, and projecting devices such as closed-circuit television (CCTV) are available. These are generally best evaluated one-on-one with a low-vision specialist.
: Patients with bilateral macular degeneration can adapt, teaching themselves "eccentric" viewing, in which they see objects by looking slightly to the side. For instance, looking at a person's shoulder could enable the viewer to see the person's face better. This makes use of one’s peripheral or paracentral vision. With conventional stronger glasses for up-close work or specialized devices, such as those determined by a low-vision exam, many people can continue read with at least one eye. Other visual aids such as larger type fonts on computers or speech-recognition programs may enable some people with macular degeneration to continue to function better in our modern world.
Patients who are concerned about changes to their vision should contact an ophthalmologist for an examination. Recent distortion or newly observed blind spots should be communicated immediately.