The Functioning of Contact Lenses: How does that work?
The way contact lenses correct our vision is actually very similar to how eyeglasses do it: they change the direction of light rays to focus the light properly on the retina.
If you suffer from nearsightedness, the light focuses too close to your eye. The light rays form a focus in front of your retina instead of directly on it. Contact lenses and eyeglasses correct nearsightedness by diverging (bending) the light rays, which reduces the focusing power of the eyes.
This moves the focus of the eye backward, onto the retina as it should be. If you suffer from farsightedness, on the other hand, your eye does not have enough power to focus. Here, the light rays fail to form a focal point when they reach the retina. This moves the point where the eye focuses forward, onto the retina.
The power of contact lenses and eyeglass lenses is expressed in diopters (D). The power of lenses that correct nearsightedness starts with a minus sign (-), and the power of lenses that address farsightedness starts with a plus sign (+).
Contact lenses are much thinner than eyeglass lenses
But how is it that contact lenses can be so much thinner than the lenses of the glasses you wear on your nose?
This is largely explained by the fact that lenses rest directly on your eye, instead of typically being a good 12 mm from the surface of your eye as is the case with glasses.
Because of this direct proximity to the eye, the optical zone of contact lenses (the central part of the lens that contains the corrective properties) can be much narrower than the optical zone of an eyeglass lens.
In fact, the optical zone of an eyeglass lens is the entire surface of the lens. The optical zone of contact lenses, on the other hand, is only a part of the lens, surrounded by peripheral fitting curves that do not affect the vision of the wearer.
You can somewhat compare it to looking out of the house through a narrow window. If you are very close to the window, you have a wide, unobstructed view of what is outside.
But if you stand on the other side of the room and then look out through the narrow window, your view of the outside world is much more limited, unless you have a much wider window.
There are videos available that explain blurred vision and its causes, and especially how you can have this condition treated.
Directly on the retina
Because contact lenses rest directly on the retina, their optical zone only needs to be about the same diameter as the part of the eye in a low light condition (about 9 mm).
If we continue the comparison with eyeglasses, the lenses of glasses must be more than 76 mm in diameter to guarantee a sufficiently wide field of view with clear vision. This wider size ensures that the lenses of eyeglasses are so much thicker than contact lenses.
Another fact that explains the thickness of eyeglasses is the reasoning that they must be so much thicker than contact lenses to avoid breaking when the glasses fall on the ground.
The lenses for nearsightedness in eyeglasses must have a minimum thickness of 1 mm in the middle, and preferably even more, to have sufficient resistance.
One of the great advantages of contact lenses is therefore undeniably that they can be made so much thinner. Most soft contact lenses for nearsightedness, for example, have a central density of less than 0.1 mm, which is more than enough to guarantee sufficient firmness and clear vision.
To summarize briefly: it is the combination of clear differences in wearing position, the diameter of the optical zone, and the required minimum thickness to ensure structural integrity that allows contact lenses to be much, even very much thinner than the lenses of eyeglasses in order to achieve the same effect.