P3.2 how eyes work

You can see because...

1) light enters our eyes through pupils

2) the light rays pass through corneas and the lens before reaching the retina at the back of the eye

3) The image at the retina, is converted into eletrical impulses by cells in the retina

4) neurones carry the electrical impulses to the brain, which interprets them

5) The iris controls the amount of light reaching the retina by making the pupil bigger or smaller. Too much light damages the retina.

1) Light rays must converge on the retina, this means the path of the rays has to be changed by the eye.

2) this refracting is done partly by the cornea and partly by the lens.

3) if the object is nearer or farther away, the shape of the lens is changed by the ciliary muscles in order to keep the image in focus on the retina.

There is no limit to how far away you can focus on disant objects, your far point is infinity. The closest you can see an un-blurred image is your near point. 

On average this is about 25cm in adults.