Page 90 - Design in Nature

88 DESIGN IN NATURE

THE STORY OF A MOMENT'S COMMUNICATION
Everybody can remember a time when his or her eyes met with an
acquaintance's eyes and they greeted one another. Would you believe that this
communication of a brief moment has a long story?
Let's assume that on a certain afternoon two men are situated apart from one
another. In spite of their close friendship, they have not yet recognised one
another. One of these men, turning his head in the direction of his friend, whom
he has not yet recognised, starts a chain of biochemical reactions: the light
reflected from the body of his friend enters the eye lens at a speed of ten trillion
photons (light particles) per second. Light travels through the lens and the fluid
that fills the eyeball before falling on the retina. On the retina there are about
hundred million cells called "cones" and "rods". Rods differentiate light from dark
and cones perceive colours.
Depending on the external objects, varying light waves fall on different
places on the retina. Let's think about the moment the person in our assumed
situation sees his friend. Some features on his friend's face cast different intensities
of light on his retina e.g. darker facial features such as eyebrows would reflect
light at much lower intensities. Neighbouring cells on the
retina, however, receive stronger intensities of light
reflected from the forehead of his friend. All of his friend's
facial features cast waves of various intensities on the
retina of his eye.
What kind of stimuli do these light waves provoke?
The answer to this question is, indeed, very
complicated. Nevertheless, the answer has to be examined
to fully appreciate the extraordinary design of the eye.

CORNEA AND IRIS
The cornea, one of the 40 basic components of the eye, is a
transparent layer located at the very front of the eye. It allows light
through as perfectly as does window glass. It is surely not a
coincidence that this tissue, found at nowhere else in the body, is
situated just at the right place, that is, the front surface of the eye.
Another important component of the eye is the iris, which gives the
eye its colour. Located right behind the cornea, it regulates the
amount of light admitted into the eye by contracting or expanding the
pupil – the circular opening in the middle. In bright light, it
immediately contracts. In dim light, it enlarges to allow more light to
enter the eye. A similar system has been adapted as a basis for the
design of cameras in order to adjust the amount of light intake, but it
is nowhere near as successful as the eye.