Page 49 - Miracle in the Eye

HARUN YAHYA

The Four Perceptions of the Retina
The retina is capable of interpreting four different properties of vision:
Contrast, color, light and shape.
Light: Under darker conditions, the rod cells are able to perceive more
light than do the cone cells. Thanks to the rods, we can see at twilight, for in-
stance. In brighter conditions, however, the cone cells come into play. This is
why the eyes of nocturnal animals have a large amount of rod cells.
Shape: Cone cells play a large part in perceiving the shape of objects. The
area of most acute vision of shapes is the fovea centralis, which has the highest
concentration of cone cells.
Contrast: The ability to differentiate between areas that are not clearly sep-
arated, but have slightly different amounts of illumination, is extremely impor-
tant. Loss of ability to distinguish contrast is common in a number of illnesses, a
condition which can bother patients even more than loss of their acute vision.
Color comes from the mind's interpretation of different wavelengths of in-
coming light. The retina separates the wavelengths, interpreting each as a dif-
ferent color.
As mentioned earlier, it is in itself a miracle that the retina can convert light
into electrical energy. But the miracles do not end there. The method by which
images formed on the retina are sent to the brain is just as extraordinary. The
retina doesn't transmit a picture to the brain as a whole. First the retina breaks
up the picture, and then these pieces are reassembled in the brain. The left-hand
side of an image ends up on the right-hand side of the retina, and vice-versa.
The pieces are transmitted separately in less than a tenth of a second, to be in-
terpreted in the brain. What's been described here is a brief summary of what
actually takes place in the retina.
The better to understand these miracles, let's examine the process in closer
detail. To see an object, the light energy entering the eye must first be converted
into nerve impulses. Beams of light cause a physical stimulation, which triggers
chemical and electrical reactions. This chain of reactions, ending with a vision of
the object, depends on a Vitamin A-based pigment called rhodopsin, found in
the rod cells.
Light striking the retina bleaches the rhodopsin. As a result of this bleach-

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