LASIK or lenses | See without glasses

In the human eye there are three structures responsible for the refractive power of the eye:

The surface-curvature of the cornea, the refractive power of the lens and the length of the eyeball just and their proportion. If the dimensions of these three elements are perfectly adjusted, the light will be focused directly on the retina and one will see sharply (=emmetropia).

In many cases, however, there are misproportions in the relation of these dimensions. We are speaking of ametropia or a "refraction anomaly".

The short-sighted eye is relatively too long. Because of that, the light passing through the eye is "bundled" before hitting the retina. Far away objects don't appear sharp. The longer the eye, the higher the grade of myopia. People suffering from myopia can see objects that are close better than ones that are distant, which leads to the term "shortsightedness".

The optical correction happens by reducing the refractive power and consequently shifting the focus further back. The necessary factors are specified on glasses or contacts (e.g. -4,5 dpt).

Hyperopic eyes are relatively too short. The light is theoretically bundled behind the retina, causing a blurred image. Younger people can balance the insufficient refractive power, because their lens will be temporarily curved only by looking into the distance. The focus will be set further to the front and onto the retina.

However, this ability will fade age, which everyone will eventually experience when looking objects that are close. The optical correction will occur by raising the refractive power with a converging lens, thus shifting the focus further to the front. The necessary factors are specified on glasses or contacts (e.g. +4,5 dpt).

The bulge of the cornea in most human eyes is equally comparable to the sruface of a sphere. Whenever the cornea is warped stronger or less strong, objects will appear blurry and distorted. Because of this a perfectly round soccer ball can appear to look like a rugby ball and a dot may be seen as a bar.

Astigmatism is commonly caused by the distortion of the cornea but it can also have its origin in the lens. This has to be checked in the preliminary investigation and is important for the choice of surgery.

Only in the case of an ideal optical system, the optical pathways apply for emmetropic as well as ametropic eyes, but the human eye exhibits aberrations: disortion of images, caused by irregularities in the optical system. We differentiate between chromatic and spherical aberrations. Although these were discovered decades ago, we were not able to measure them in the eye. Due to the development of machines to measure aberrations, new possibilities are being established concerning diagnostics as well as treatment of several kinds of sight disorders (chromatic aberrations remain unconsidered).