In the case of a healthy eye, the rays of light entering the eye pass through the cornea, pupil, and then the lens of the eye and meet the retina, the place of acute vision, thus creating a sharp image of the environment. The refractive power of the eye depends on the refractive power of the lens and cornea and the length of the eyeball. In case of a refractive error, due to a deviation of one of these factors, the light rays do not meet at the area of sharp vision, the macula. Based on this, nearsightedness (myopia), farsightedness (hypermetropia), astigmia and presbyopia can occur.
In the case of myopia, the light rays meet in front of the retina due to the longer eye axis or greater refractive power of the cornea, so the retinal image is blurred and the individual sees distant objects dimly. It can be corrected with glasses, contact lenses, laser eye surgery or with lens replacement surgery over the age of 45.
​In the case of farsightedness (hypermetropia), due to the shorter eye axis or lower refractive power of the cornea, the light rays would meet behind the retina, so the retinal image is also blurred in this case, but these individuals see clearly at a distance and out of focus up close. In this case too, the solution is glasses, contact lenses or laser eye surgery.
In the case of astigmia, the refractive power of the eye is different in different meridians, this results in the fact that the rays of light arriving at the eye cannot meet at one point on the retina, and the image is blurred both near and far. The solution is cylindrical glasses with contact lenses or laser eye surgery.
Presbyopia starts over the age of 40, when the lens of the eye becomes less flexible as it ages and is no longer able to focus light rays from nearby objects on the retina. This is when reading glasses become necessary, but vision-improving lens replacement can also be a solution, which also offers a long-term solution to age-related cataracts (loss of transparency of the eye lens).