This is a post on the eye condition ‘wet’ macular degeneration (WMD), there will be about as much of the other sort of WMD as there were in Iraq. I was at a conference on mathematical biology a couple of weeks ago, and heard some great talks. One of the most inspiring was on what is called ‘wet’ macular degeneration. Before the talk started I did not even know what the macula was.
The macula is basically the part of the retina responsible for seeing the centre of our field-of-view where we see in detail (as opposed to peripheral vision which is done using other parts of the retina). The image above is taken looking into a healthy eye, the macula is the bit in the middle of this image. When people get macular degeneration the macula degenerates and their vision is greatly impaired. This, almost always, occurs in the elderly. There are two types, and ‘wet’ or neovascular macular degeneration is the less common but faster progressing form.
‘Wet’ is the common name but it is not very descriptive, the macular degeneration is caused by new (neo is from the Greek for young) growth of capillaries (vasculature), hence the rather more descriptive name neo-vascular macular degeneration. Basically, the retina has a layered structure, like a cheese cake, with the cells that detect the light on top, and the capillaries that supply the oxygen and nutrients that the light-detecting cells need, underneath.
The two layers are kept apart by a membrane: Bruch’s membrane. Now, like a lot of our body the macula, in particular the capillaries, are quite dynamic, throughout our life cells die, cells are born, and capillaries can re-route. That is fine, but the capillaries must keep below Bruch’s membrane and out of the top layer. If growing capillaries invade the layer of light-detecting cells they disrupt and damage it. This is exactly what happens in neovascular macular degeneration. The capillaries grow through Bruch’s membrane and these growing capillaries mess up the light-detecting layer, damaging vision.
I found it slightly surprising that a disease of ageing is caused by new capillary growth. But that is what happens. So, the talk by an American prof, James Glazier, put forward a new idea for what causes these capillaries to grow. This is that in the ageing eye the adhesion between cells in the macula weakens. This allows growing capillaries to push between the cells of the macula and disrupt vision.
Although we don’t usually think about it, our cells stick to each other, and that is crucial. If they did not stick together our bodies would fall apart into a big pile of about 100 trillion individual cells!
I don’t know if this idea is right, although the talk included some pretty convincing modelling that show that it could work. But I think it was good science, it has a good idea, one that is interesting, testable, and important (WMD is not curently curable). It may not be true, but if it is it could tell us how to treat quite a nasty condition.
