vision....?

Question

Is it correct to say that the human eye can only see in straight lines?

because...how else would you explain that when you see things in water, even though they have been refracted and do not lie parallel to the original path of light, humans still see it to be higher/lower than really is?

Answer 1

In two senses the human eye 'sees' in straight lines. First, what the eye actually sees are photons (tiny packets of energy traveling at the speed of light in straight lines). Secondly, the human eye uses its fovea during the day to concentrate light from a small object we focus upon onto the most sensitive detailed vision receptors of the eye which are very rich with color detecting cones. As such there is a line of sight from the object through the eye's lens to the 'sweet spot' of the eye. At night the color cones function poorly and the black & white receptor rods outside the fovea can see better in dim light. In fact it is often easier to see something at night if you look slightly to one side of it. The rods permit peripheral vision like seeing out of the corner of your eye which attracts the attention of the fovea. When light enters water (or thick glass or lenses) the stream of photons is bent (refracted) taking a shorter path (than in a perfect vacuum) but what you see is the stream of photons (in a straight line) after they emerge from the water (or glass).

Answer 2

No. The human eye sees in a sort of partly spherical vision. We will not have the periperl vision if we are seeng only in straight lines.