The working of the eyes is often compared to the way a camera operates.
Let's look at that analogy, and see where it holds true and where it breaks down.
The camera has a lens to focus the light, a way to control the focusing,
a shutter to let in the desired amount of light, and film that holds the image.
The eye has a lens, a focusing mechanism (controlled by the ciliary muscles), an iris (which adjusts the amount of light entering the eye through the pupil),
and a retina (where the image is recorded)
In a camera, for the image to be clear it must be focused on the film. Likewise, in the eye, the image must be focused on the retina (film)..
In a nearsighted eye, rather than the image registering precisely on the retina, it is focused in front of the retina. (Fig. 2B) Thus, one conclusion is that the eyeball is too long.
In a farsighted eye, the opposite happens: The image is focused behind the retina. (Fig. 2C) Here, the conclusion is that the eyeball is too short.
If these conclusions are true, how did the eyeball lose its natural shape?
There are six muscles that surround each eye and control eye movements.
They move your eyes up, down, to the right and to the left.
When you look at something up close they turn the eyes in (converge) and when you look at a distant object they turn the eyes out (diverge).
These extra-ocular muscles are 150 - 200 times stronger than they need to be.
Tension in these muscles causes eye movements to become more rigid and less flexible.
In 1981, research performed by Peter Greene at Harvard University showed that when these muscles hold the eyes in one position for an extended period of time, they also squeeze the eye.
And, that under the right conditions, this pressure can change the shape of the eye. But this is not the whole story.
Let's return to the camera analogy for a moment. In the camera, the lens moves in and out to bring objects at different distances into focus.
This doesn't happen in your eyes. Instead, the lens changes its shape to bring objects into focus.
When focusing on a near object, the lens becomes fatter, bulging from front to back. To focus on something farther away, it becomes thinner.
We are always changing what we are looking at, so the lens is continually making fine adjustments in its shape.
Normally, the lens changes its shape — and its focus — more than 100,000 times every day.
The shape of the lens, and thus its focusing ability, is controlled by the ciliary body, which surrounds the lens.
There is a constant and delicate interplay among the muscles and ligaments of the ciliary body.
They work together to change the lens into the exact shape required to bring whatever you are looking at into sharp focus.
In the normal eye, the muscles are constantly readjusting their pull on the lens — changing the focusing power by changing its shape.
The muscles and the lens are flexible, and are able to adjust and re-adjust to bring objects at near or far distance into clear focus.
This process is called accommodation.
The nearsighted eye can see near objects clearly, but not distant objects. It is “stuck” for near vision, changing its shape only enough to bring near objects into focus.
To see distant objects more clearly the lens needs to flatten (become thinner) to bring distant objects into sharper focus.
The farsighted eye can see distant objects clearly, but not near ones. It is “stuck” for distance vision, changing its shape only enough to bring distant objects into focus.
To see near objects more clearly the lens needs to become thicker to bring nearer objects into sharper focus.
If the image isn't focused on the retina, it could be due to a decreased flexibility of the ciliary body, not a distorted shape of the eye.
In fact, the lens has such a great range of focusing ability that it could easily compensate for any supposedly abnormal shape that the eye may have become.
Clear vision isn't only determined by the strength of the eye muscles. And it isn't just a matter of the shape of the eye.
Instead, clear vision requires that all parts of the visual system — ciliary body, lens, extra-ocular muscles, shape of the eye — work together and function in harmony with flexibility and coordination.
And this coordination is ultimately a reflection of how the mind controls the eyes — which can be changed and retrained.