Age-related Macular Diseases
Age-related macular diseases (AMD) affect about 30 million people worldwide. They are the leading cause of losteye sightin people who are over 50 years of age in developed countries. The macula, which is a small central area of the retina of the eye responsible for detailed vision, gradually degenerates and causes loss of central vision, significantly affecting our daily activities, such as reading, driving and recognizing faces.AMD is not painful; progression can be rapid or slow and can affect one or both eyes. When AMD progress slowly, our brain may be able to adjust and react successfully to it and we may not discern its symptoms. Conversely, if AMD progresses rapidly, we usually will notice vision loss. Serious AMD can cause permanent vision loss if not treated promptly.
There are two forms of AMD: dry and wet. Dry AMD is the most common type and accounts for about 90% of all AMD cases in the early and middle stages. The early stage of dry AMD is usually accompanied by an accumulation of drusen, which aredebris of the photoreceptor epithelial cell layer deposits within the macular. As our eyes age, there are various sizes and shapes of drusen deposits that accumulate within the retina. In the early stage, there is little vision change even though there may be many small and medium sized drusen formed. As the disease progresses into the middle stage, small or large size drusen appear; at this point, the symptoms of macular degeneration start to be noticed: straight lines become distorted or curved and dark spots appear in our central vision field making reading nearly impossible.Also, during the middle stage of AMD (dry or wet), the drusen may enlarge and increase in number as photoreceptor cells and their surrounding tissues degenerate; this is called map-like degeneration which causes dim central vision, decreased intensity or brightness in color and/or increased difficulty in recognizing small words or adapting to dark surroundings.
As previously mentioned, AMD may affect one or both eyes. When one eye loses its vision, it may not be noticed because the good eye is able to compensate for the weak eye. Thatisjust one reason to have regular eye checkups.
AMD causes subretinal blood vessels to sprout. These growing blood vessels abnormally leak, allowing fluids and blood to seep into the layers of the macular and accumulate between the layer of the Bruch’s membrane and photoreceptor cells, damaging the optic nerve required for vision. An accumulation of fluid in the macular looks likes a blister; it can cause the distortion of straight lines and createthe appearance of black spots in our central vision. If left untreated, bleeding due to leaking blood vessels can cause scarring oftissue and permanent vision loss. There are several treatment options available that can halt or slow vision lost due to wet AMD. If treatment is applied early before the occurance of scarring, it is possible to restore some vision for some patients.
What is angiogenesis?
Angiogenesis is the physiological process in which new blood vessels form from pre-existing blood vessels; it is a normal process that occurs during the phases of wound healing and reproduction; other typesof angiogenesis are considered to be aberrant. Wet AMD causesnew blood vessels to grow anomalously in the macular, resulting in damage to the central retina. These new aberrant blood vessels are usually fragile; if left untreated, blood and protein leakage can cause edema in the retina. Scarring from these blood vessels eventually affects visual functioning and results in permanent vision loss.
How do new blood vessels grow?
- There is a specialized protein growth factor that can stimulate and activate new blood vessels to grow;
- This primary growth factor, called Vascular Endothelial Growth Factor (VEGF), is then produced in the layers of theretina in patients with wet AMD;
- Excessive VEGF can cause new blood vessels to sprout from preexisting vessels;
- These growing blood vessels are very fragile, allowing fluids or blood to leak;
- The growing vessels continue to form lumen;
- Pericytes accumulate and stabilize the structure of these newly formed vessels; and
- Other specialized stem cells, called endothelial progenitor cells exist in bone marrow under the normal condition. These endothelial progenitor cells, receive signals to migrate and circulate around newly formed blood vessels during the process of angiogenesis.
Risk factors related to AMD:
- Aging: It is the strongest predictor of AMD, especially if one is over 60 years old;
- Family history: Family members with AMD may have a higher chance of gettingit;
- If one eye is diagnosed with AMD, the other may be predisposed to AMD;
- Smoking: Smoking increases the risk of acquiring AMD by 2 to 3 times. Quitting smoking can lower the risk of getting AMD;
- Gender: AMD is more common in women than in the men;
- Obesity: Being overweight increases the potential of developing advanced AMD;
- Hypertension: People with uncontrolled hypertension are more likely to get AMD; and
- Eat lots of green, leafy vegetable, fruits and fish regularly. These foods contain natural antioxidants whichcan inhibit angiogenesis.Avoidfoods containing high saturated and artificial fats also helps.
Diagnosis of AMD:
- Amsler grid;
- Fundus photography;
- Fluorescence angiography; and
- Three-dimensional optical coherence tomography (OCT).
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