The eye

The structure of the eye resembles a camera. It contains image-projecting organs, the refractive media: cornea and lens. The image-receiving organ is the retina.

The front part of the eye – the cornea - has 2/3 of the eye’s refractive power, the lens of the eye 1/3. They both perform the same task, like a camera lens. In a healthy eye, both the cornea and lens are clear; any cloudiness in one or both organs can lead to a reduction in visual acuity.

The lens consisting of a nucleus and a cortex, is surrounded by the lens capsule, which is attached with elastic fibers – the zonular fibers – on the ciliary body of the eye behind the iris.

The pupil fulfills the function of a shutter. Its width is determined by the muscles in the iris, according to the intensity of the light.

The retina can be likened to photographic film. The light rays falling upon it are converted into electrical stimuli and passed on via the optic nerve to the visual center in the brain, where the actual image is formed.

Eye anatomy

In the same way as the camera lens focuses the light rays onto a photographic film, the cornea and lens have to gather the light entering the eye onto the retina. Sharp images can only be seen if their refractive power exactly matches the length of the eye. The point at which the light rays are focussed on the retina is called the macula lutea.

This point of “maximum visual perception” is only a tiny part of the retina, but essential for the ability to read. The remaining 98% of the retina forms the “field of vision” which is essential for the perception of all movements and objects in the outer periphery. If the refractive power of the cornea and the lens does not perfectly match the length of the eyeball, the result is a visual disorder. There are various causes for this.

Generally the eyeball is too long (nearsightedness) or too short (farsightedness). At the same time an irregular astigmatism can cause distorted images. This is known as astigmatism. Previously correction of these visual disorders was only possible using glasses and contact lenses.