Sehfehler: When the eye weakens

Being able to see the world clearly with your own eyes is a gift. Nature does not exist for everyone. Short and long sight force millions of people to wear glasses or contact lenses. Good vision has its origin in the imaging of sharp images on the retina of the eye. The optical system of the eye deflects incoming light rays (images we see) so that they meet in a focal point on the retina in normally focused eyes, usually at the point of sharpest vision. This distraction is called refraction.

When do you talk about a visual sight?

From the various parts of the optical system of the eye (especially the cornea and the lens), the total refractive power is given, which is given in diopters (dpt). When the power is correct, images we see are sharply imaged on the retina.

If the focal point is not exactly on the retina, ie before or behind it, the environment is blurred. One speaks of a refractive error or a refractive error, colloquially also called visual defects.

At the refractive errors we distinguish:

  • myopia
  • hyperopia
  • Astigmatism (astigmatism)
  • presbyopia

The most common is the correction of a refractive error using glasses or contact lenses.

Normal eye

The focus is exactly on the retina: foreground and background are perceived sharply.

No correction required.


The focal point of the incident light rays is not on, but in front of the retina: distant objects are perceived blurred.

Correction example: Sph: - 3.5 dpt


The eye is usually too short grown, the light rays are therefore only bundled behind the retina: Nearby objects appear blurred.

Correction example: Sph: + 1.5 dpt


The light rays are broken differently and do not meet at one point, but scattered on the retina. The reason for this is usually the cornea, which is more like an egg than a ball. A point in nature becomes a line in the perception ("astigmatism"): objects, both near and far, appear distorted.

Correction example: Cyl: 0.75 / Axis 90 ° (often occurs in combination with short-sightedness or farsightedness)


As people get older, the ability of the eye lens to focus automatically on different distances will increase with each person: nearby objects appear blurry.

Correction example: Add: + 2.5 dpt

Visual aids as a limitation?

Not always wearing these tools is free of problems. In particular, wearers of glasses often feel impaired in their daily lives, during their free time or during sports. Contact lens wearers may develop intolerances, irritations or allergies to cleansers.

Therefore, it is not surprising that eye surgeons have been trying for forty years to develop procedures that can be used to surgically eliminate malformations. Thus, with the development and improvement of new surgical procedures, a new specialization in ophthalmology emerged: refractive surgery.

Refractive surgical operations

Through an operation is sought to correct the individual refractive power error so that the light rays or images are sharply imaged on the retina without additional optical aids. Depending on the technique used or the site of intervention, a distinction is made between laser, incision and implantation procedures or lens and corneal procedures.

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