In Response to WordPress daily prompt: (Your Thing) for Dummies: Take a complicated subject you know more about than most people, and explain it to a friend who knows nothing about it at all.
Consider our eyes as a mean to capture lights for our brain to see. This statement is true, you know, because they actual act of “seeing” occurs in the brain. Our eyes are simply the set of lens to capture the lights so our brain can process.
Sometime, our eyes can have defect. This defect cause the lights captured by our eyes to be distorted, or imperfect. The most common defect is myopia, or nearsightedness. Eyes with myopia unable to correctly focus the lights from distant object on retina, the brain’s light receptor. Because of this, the brain received poor lights signal, and see blurred image from distant object.
There are a lot of cause of why our eyes unable to focus the lights properly. Each of our eyes has a lens that help it to focus. The lens’ power can be modified by action of our eye’s muscle. Hypothesis tells that, sometime the eye muscles stuck the lens to focus to near vision. Other hypothesis says that nothing wrong in the eye muscles. It is the shape of the eyes that change from circle to oval. But both agree that this is due to excessive near work that make the eyes think that they no longer need to focus to distant object. Near vision in normal eyes stress them out. So, the eyes adjust to be less stressful. In extreme case, both the lens and the shape of the eyes adjusted, which is causing severe myopia.
So, to remedy this, we need to change the focusing power of the eyes. It is done by using using external lens in front of the eyes, such as eyeglasses & contact lenses, or reshaping our eyes’ lens, such as LASIK. The external lens is measured by diopters. Lens to correct myopia is measured with negative diopters. The higher the number, the thicker the lens, and the closer a thing need to be to the eyes for our brain to see clearly without external lens. The relation of lens power and maximum distance of things to be seen clearly without the lens are approximately as follow:
- Eyes that need -1 correction can see things clearly for maximum of 1 meters
- Eyes that need -4 correction can see things clearly for maximum of 25 cm. This is the normal reading distance. Beyond this, it is uncomfortable to read without glasses.
- Eyes that need -10 correction can see things clearly for maximum of 10 cm. This is pretty close to your nose, and considered as severe myopia by most standard
If you are wondering how blurry the world can be without glasses, I have post several simulation of how I see without glasses. My eyes need -12 correction to see distant object clearly. And by distant, it means that anything beyond 8 cm or so.