An up-close look at how we see Where do you see? In your eyes or in your mind? It is a question that has perplexed many in medicine for centuries. The answer is both. The complex act of seeing can be broken down into three basic steps: |
| Step 1: Light rays, or photons, enter the eye's outer, transparent layer of tissue (the cornea), then pass through the dark, circular opening (the pupil) in the center of the colored iris. The pupil regulates the amount of light that enters the eye. |
| Step 2: The light rays strike the inner (or crystalline) lens of the eye. This lens focuses the rays on the retina -- a layer of light-sensitive cells that line the inside back wall of the eye. |
| Step 3: The cells in the retina transform the photons into electrical impulses. These are transmitted through the optic nerve to the brain, where complex electrical-chemical interactions give us the sensation of seeing. |
| The electrical and chemical communications that take place between the retina and the brain are fascinatingly complex. They are so complex, in fact, that it's difficult to know whether seeing actually takes place in the eye or in the mind. The best way to picture it is to say that the eye creates the electrical impulses and the brain sorts them all out. |
| Inside the Human Eye |