The mechanism for Age-Related Macular Degeneration

Age related macular degeneration is not yet fully understood, but the research being done by this and other research groups around the world is helping us to gain more knowledge of how this disease comes about.

The macula is a small region at the centre of the retina that gives us our clear vision. 

The Macula

Normal fundus

Causes of AMD

Over the period of our lifetime, damage is done to this sensitive part of the eye in mainly two ways. 

1. The first mechanism of damage is blue light.

The electromagnetic spectrum spans very short wavelength radiation from gamma rays, x-rays, ultraviolet light, the visible spectrum, up to long wave radiation including infra-red rays and radio waves. The shorter wavelength radiation is more damaging to the human body. For example, if you ever go to have an x-ray done, the radiologist wears protective shielding and will stand behind a protective screen to prevent damage from the x-rays.

Ultraviolet light is know to cause damage, especially to the skin. The lens inside the eye behind the iris will absorb the damaging ultraviolet light, which can be a cause of cataract. The next most damaging radiation is the blue light that reaches the back of the eye. This blue light causes 'oxidative stress' damaging the structures at the back of the eye.

 2. Free radicals

By-products of oxygen metabolism known as free radicals can cause damage to the cells of the body. These unstable molecules are neutralised by anti-oxidants which we get through our diet.

Types of AMD

Traditionally, AMD has been classified into wet and dry forms. However, we feel it is better to characterise them into early and late forms. This helps to also distinguish somewhat the difference between AMD where vision is largely unaffected and visually consequential AMD.

1. Early macular degeneration

This is the first stage of macular degeneration
There is no definite treatment for early macular degeneration, although increasing macular pigment levels seems to have some beneficial effects
It is caused when drusen, deposits of lipofuscin form at the macula
It tends to develop slowly, causing some deterioration in central vision, blurry vision, and seeing objects in a distorted manner

Large soft drusen

2. Late macular degeneration

We can subdivide late AMD into two categories - late dry or geographic atrophy and late wet or CNV (choroidal neovascularisation).

About ten per cent of people with the early form of macular degeneration will go on to develop the late form.
Geographic Atrophy is called thus because it has a discrete demarcated area around the macula which do not correspond to any physical structures.
CNV is the formation of new fragile blood vessels in the choroid the layer below the retina underneath the macula. These delicate blood vessels can leak or bleed causing a rapid damaging affect on vision.

Choroidal neovascularisation

A video showing the course of AMD

Below is a video showing how AMD occurs and the visual symptoms associated with this debilitating condition. It shows the formation of drusen first - early AMD, which then progresses to the wet form with leakages and haemorrhages.