The eye is a complex optical system made up of the cornea, crystalline lens and vitreous body, which deflects or refracts incoming light. The total power of refraction from all these optical components is expressed in dioptres (dpt). In a normal-sighted eye the rays of light are refracted so that they land at the exact centre of the retina – at the point of best vision. Images are thus perceived in focus.
If the focal point does not fall exactly on the retina, but instead in front of or behind it, the object viewed is represented in a blurred manner: This is known as defective vision. Distinctions are made between near-sightedness, far-sightedness, astigmatism and age-induced far-sightedness.
The focal point of a normal-sighted eye is exactly on the retina for objects close up and at a distance. This is why close objects and distant objects are perceived clearly.
|Femto-LASIK/LASIK||up to -8 dpt||up to +3 dpt||up to 4 dpt||possible|
|LASEK/PRK||up to -6 dpt||up to +1 dpt||up to 3 dpt||possible|