We took this picture to show you what happens when several beams of light encounter a lens.

When nothing gets in its way, light travels in a nice straight line. But when you put a chunk of clear glass or plastic in the way, light may not keep traveling straight. If light encounters a piece of glass or plastic at an angle, the light bends. The bigger the angle, the more the light bends. The light may bend again when it moves from inside the glass or plastic into the air. If the light meets the air at an angle, the light bends. The bigger the angle, the bigger the bend.

The beams of light shine through the clear plastic of the lens and encounter the curved surface where the plastic of the lens meets the air. Beams of light that meet this surface straight on keep on going straight. But some beams of light meet the curved surface at an angle. Those beams bend. This lens is curved on one side and flat on the other. The lens in your eye is curved on both sides, but it works in the same way.