Question: in short, are cells in the eyes actually functional when you go blind? Is blindness a result of a bad connection between the eyes & the brain or is it something inside the eye?

Stephen Moss answered on 14 Mar 2011:

These are great questions, with lots of ‘yes and no’ type of answers. Most often, when you go blind it’s because one type of cell in the eye (rather than the brain) has gone wrong. There are about 5 or 6 major cell types that between them collect light at the back of the eye and transfer the information to the brain. Often, one type of cell will die, but the others are all fine and properly functional. But sometimes it’s a really key ‘support’ cell that dies, and then many other cell types will die too. So there’s no single rule about what happens.

However, occasionally, the connection between the brain and eye can go wrong. For example, in some patients with multiple sclerosis the optic nerve can slowly degenerate so information no longer flows from eye to brain. In fact, the optic nerve is a bundle of millions of long nerve cells that extend from the eye to the brain. In another condition, glaucoma, those nerve cells, which have their nucleus in the eye, slowly degenerate, and again there is a loss of communication to the brain.