What causes age-related macular degeneration?
In people with ARMD the cells of the retinal pigment epithelium do not work so well with advancing age. They gradually fail to take enough nutrients to the rods and cones, and do not clear waste materials and 'by-products' very well made by the rods and cones. As a result, tiny abnormal deposits called 'drusen' develop under the retina. In time the retinal pigment cells and their nearby rods and cones degenerate, stop working and die. This is the 'dry' type of ARMD.
In some cases, something also triggers new blood vessels to develop from the choroid to cause the 'wet' form of ARMD. The trigger is not known. It may be that some waste products which are not cleared from the retinal pigment epithelium may stimulate new blood vessels to grow in an attempt to clear the waste. The exact reason why cells of the retinal pigment epithelium stop working properly in people with ARMD is not known. Certain 'risk factors' increase the risk of developing ARMD. These include:
- Smoking.
- Possibly, high blood pressure (inconclusive evidence).
- A family history of ARMD. (ARMD is not a straightforward hereditary condition. However, your risk of developing ARMD is increased if it occurs in other family members.)
What are the symptoms of age-related macular degeneration?
- The main early symptom is blurring of central vision despite using any glasses that you need. In the early stages of the condition you may notice that:
- You need brighter light to read by.
- Words in a book or newspaper may become blurry.
- Colours appear less bright.
- You have difficulty recognising faces.
- A particular early symptom to look out for with wet-ARMD is visual distortions. Typically, straight lines appear wavy or crooked. (For example, the lines on a piece of graph paper, or the lines between tiles in a bathroom, or the border of any other straight object, etc.)
- A 'blind spot' then develops in the middle of your visual field. This tends to become larger over time as more and more rods and cones degenerate in the macula.
ARMD is painless. Symptoms of dry-ARMD tend to take 5-10 years to become severe. However, severe visual loss due to wet-ARMD can develop over weeks or months. Therefore, see a doctor or optometrist quickly if you develop visual loss or visual distortions as treatment may be possible. Peripheral vision is not affected with ARMD and so it does not cause total blindness.
Note: if the vision of one eye only is affected, you may not notice any symptoms as the other good eye often compensates. When both eyes are affected you are more likely to notice symptoms. Therefore, older people should have regular eye checks to check on each eye separately for early ARMD (and to check for other eye conditions such as glaucoma.)
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