Page 12 - The Book Pi in eye

Rajesh Khanna, MD

lobe. On the way, half the fibers from each eye cross over to the
other side. It results in half the fibers from the right eye reaching the
left occipital lobe. This super specialized area of the brain develops
the electrical signal into images, which is interpreted by the higher
centers of the brain. The neuroelectric pathway from the retinal
receptors to the occipital lobe, need to be functioning properly for us
to enjoy the sensation of vision and perceive the world. Glaucoma,
which affects optic nerve, can lead to defects in vision. Strokes or
tumors in the region of the optic pathways can cause blindness in
half the field of vision. If occipital lobe has a decreased blood supply
or bleeding, it results in cortical blindness.
The eye is an engineering marvel; it is dynamically assembled, and
must modulate its converging power to see things at different
distances. The eye can be compared to a highly sophisticated camera,
because of the similarity between the lens system of camera and the
human lens. The camera film or computer chip is similar to the
macula of the retina. In turn, the beams of light must be brought to a
focus onto photographic film or a chip, which can be compared to
the retina of the eye. Basic optics tells us that objects at different
distances will be brought to focus at different points. Some of these
may be in front of the retina, some on the surface of the retina, and
others behind the retina.
We can only see the image, which falls, onto the retina, which is in
fact an extension of the brain. It then becomes imperative, that to
enjoy the natural world, we need to have a mechanism to adjust the
focal length of the eye.
Unfortunately, it is not possible to adjust the focal length of the
eye. Instead the option of modulating the focusing power of the lens
is used. This is achieved by a dynamic change in the curvature of the
lens, which results in a corresponding change in the power of the eye.
The lens is formed in the eye while one is still in their mother’s
womb. After birth, the lens continues adding new material for the
rest of one's life.
Physically, the human lens is a clear oval biconvex shape (like a
magnifying glass), which can change curvature as needed. In youth
the lens changes its curvature to adjust its power and retains the
image on the retina. Age begets an older thicker lens. Curvature
adjustment becomes progressively difficult chore and finally failing by
sixty years of age.

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