The causes are still not fully understood, however a lifetime of exposure to UV light, production of free radicals and reduced blood flow to the retina may result in abnormal changes in the thin pigmented layer called the retinal pigment epithelium (RPE).
There are two categories of AMD:
- DRY: In the early stages there is an accumulation of yellowish deposits called drusen, as well as a loss of pigment cells in the RPE. This may progress with greater areas of pigment degeneration and scarring. This will result in greater blur in the central vision. 90% of AMD is the dry form.
- WET: This occurs when abnormal blood vessels under the retina start to grow up through the retina and the breaks in the pigment layer. These new blood vessels are weak and porous and tend to leak and bleed quite easily. This can result in fluid build up and swelling, as well as bleeding (hence WET). In this case damage to the macula and loss of vision can be very rapid. If not treated promptly, the fluid can leave significant scars which result in permanent severe loss of central vision.