Human eye: an optical instrument
The human eye can be considered an optical instrument: it forms images by the physical phenomenon of refraction, in which light undergoes deviations when changing medium.
Image formation in the human eye
The image we see is the result of the following process: the lens , a biconvex lens, forms a real and inverted image of the object, which is located exactly on the retina . After this process , this image is sent to the brain by the optic nerve . After numerous complicated processes, which make it stay in the correct position, we see the object clearly.
We can see objects clearly because their image is formed on the retina, however, there are some cases in which it is not formed exactly on the retina, causing what we call vision defects . These defects occur due to a possible deformation of the eyeball or even a defective visual accommodation. They can be corrected using eyeglasses , contact lenses, or laser surgery .
In myopia, the image forms in front of the retina. To correct this defect, that is, for the image to form exactly on the retina, the person who has this problem must wear glasses with diverging lenses.
In hyperopia, the image of the object is formed behind the retina. To correct this vision defect, the person must wear glasses with converging lenses, which make the image of the object form exactly on the retina.
It is important to emphasize that there are not only these two cases of vision defects and that, for each problem, there is a type of lens with specific characteristics that allow the user to see the object clearly.