Re: What causes the nerve cells at the back of the eye to die?

A good question Elizabeth, and you are lucky, I have done research in the area of glaucoma myself. You can read about glaucoma at many excellent sites on the internet, and about other major blinding eye diseases too, at the Eye Research Network Website ....but here is a fast summary for you as well:

The eye has two liquid filled chambers in front of and behind the lens. The aqueous humor is the liquid in the front of the lens. Refer to this eye image (from the ERN site):

(Click on the image to see a larger version)

So nutrients are supplied to the lens and the cornea by the flow of the aqueous humor. It starts near where the lens is attached and flows and squeezes past where the iris almost touches the lens, continues into the front chamber where the cornea can get some nutrients from it....then it leaves the eye. The front chamber of the eye, is surrounded by the cornea, the iris and the front of the lens as you can see. Where the iris meets the cornea, you can see it forms an "angle". In that corner angle is a meshwork called the trabecular meshwork... and that is where the aqueous humor leaves the eye. In most glaucoma, the biggest risk factor is elevated intra ocular pressure, pressure in the eye. It gets too high...because the flow of aqueous humor out of the eye starts to get blocked off. But the ciliary epithelial cells are still trying to pump in new aqueous humor fluid. So it is like pumping up a tire, the pressure goes up if you try to pump in with no outlet.

So now you know that the eye pressure is rising above normal. Why is that bad?? Well..... you can see the optic nerve in the diagram, it is a collection of millions of nerve fibres from the retina. The nerve signals from the retina's photoreceptors send signals all the way into the brain, and the optic nerve is just a bundle of all those communication fibers. When the eye pressure goes too high, the optic nerve is pushed out too far. The optic nerve passes through a hole in the sclera (a very tough covering to give the eyeball strength and flexibility). It is like having a cork in a hole on a balloon. If you pressurize it too much it will try to push the cork outward. In the eye elevated pressure in the eye pushes the nerve out and stretches the fibers more than they should be stretched. That can kill those nerve cells. Also, when the pressure gets too high, it is higher than the pressure in the blood vessels feeding the retinal neurons. It is hard for nutrients and oxygen to be pumped from the blood stream into the liquids bathing the cells when the pressure is too high outside the blood vessels. So, the optic nerve may get less oxygen than it requires as well.

So, glaucoma is often treated with eye drops that cause the ciliary epithelial cells to make LESS aqueous humor, ie. turn down the pressure pumping into the eye. Some times that is not enough, and surgeons make extra holes in the angle of the eye to give the pressure a place to leak out into the sclera. While glaucoma is treated in this way, it is often not perfect fix. Glaucoma is not painful either, so many of us have high eye pressure and do not know it. Many people find out they have glaucoma only when they start to loose site, and then it is too late. So it is important to have your eyes checked (including eye pressure) every year, especially if you are over 40.

Read more on eye disease and eye research at :

Eye Research Network Website

January 2000 was Glaucoma Awareness Month - National Eye Institute

Ken Mitton, PhD

Dept. of Ophthalmology and Visual Sciences

Kellogg Eye Center, University of Michigan Medical Center