Being able to see the world clearly with your own eyes is a gift. Nature does not give it to everyone. Nearsightedness and farsightedness force millions of people to wear glasses or contact lenses. Good vision originates in the imaging of sharp images on the retina of the eye. The eye’s optical system deflects incoming light rays (images we see) so that they meet at a focal point exactly on the retina, usually the point of sharpest vision, in normal-sighted eyes. This deflection is called refraction.
When is it called a visual field defect?
The various parts of the eye’s optical system (primarily the cornea and the lens) result in the total refractive power, which is expressed in diopters (dpt). If the refractive power is correct, images that we see will be sharp on the retina.
If the focal point is not exactly on the retina, i.e. in front of or behind it, the surroundings will be blurred. This is referred to as a refractive error or defective vision, colloquially also called visual defect.
We distinguish between the refractive errors:
- Nearsightedness
- Farsightedness
- Astigmatism (astigmatism)
- Presbyopia
The most common is the correction of refractive error by means of glasses or contact lenses.
Normal eye
The focal point is located exactly on the retina: Foreground and background are perceived sharply.
No correction required.
Nearsightedness
The focal point of the incident light rays is not on, but in front of the retina: objects further away are perceived out of focus.
Example of correction: Sph: – 3.5 dpt
Farsightedness
The eye is usually grown too short, therefore the light rays are focused only behind the retina: Objects in the vicinity appear blurred.
Example of correction: Sph: + 1.5 dpt
Corneal curvature
The light rays are refracted differently and do not hit the retina in one point, but scattered. The reason for this is usually the cornea, which is more like an egg than a sphere. A point in nature becomes a line in perception (“astigmatism“): objects, both near and far, appear distorted.
Correction example: cyl: 0.75 / axis 90° (often occurs in combination with nearsightedness or farsightedness).
Presbyopia
As everyone ages, the ability of the lens of the eye to automatically focus at different distances diminishes: Nearby objects appear out of focus.
Correction example: Add: + 2.5 dpt
Visual aids as a limitation?
Wearing these aids is not always free of problems. In particular, spectacle wearers often feel impaired in daily life, leisure or sports. Contact lens wearers may develop intolerances, irritations or allergies to cleaning agents.
It is therefore not surprising that ophthalmic surgeons have been striving for a good forty years to develop procedures that can be used to surgically remove defective vision. Thus, with the development and perfection of new surgical procedures, a new specialization in ophthalmology emerged: refractive surgery.
Refractive surgery operations
Surgical intervention aims to correct an individual’s refractive error so that light rays or images are sharply focused on the retina without the need for additional optical aids. Depending on the technique used or the site of surgery, a distinction is made between laser, incision, and implantation procedures or between lens and corneal procedures.