Finally, some time is spent looking at the human eye. It consists of a spherical organ with a transparent lens, and a photosensitive region filled with several different types of photoreceptor cells. The different shapes of the photoreceptor cells serve to offer sensitivity to different colors of light. Their locations are also highly specialized to optimize the absorptivity.
Fig 3. Human Visual System
An interesting thing to consider is the appearance of animal eyes at night. When illuminated, they actually appear to be reflective.
What advantage is there in this?
The human eye has a nerve bundle which runs from all of the photoreceptors to the nervous system positioned on the back surface of the eye. This location does not have any photoreceptors, and so there is a 'blind spot' in human vision. Have you ever noticed it?
Fig 4. Finding Your Blind Spot
By looking at the picture of the rat above, it is possible to notice your blind spot. Cover your left eye, and hold the drawing about 30 cm from your eye. While looking at the upper 'X'. you should notice that there is a distance from your eye at which the spot disappears. On the other hand, if you look at the lower 'X', you should find that the rat disappears, but that the lines seem to stay.
What is the explanation for the above phenomenon?
