Vision is one of the most complicated processes in our body. Through the perfect interaction of cornea, lens, retina, vitreous body, optic nerves and finally brain, we are able to see and understand an image. However, almost every second German has problems with vision. Read what nearsightedness and farsightedness are and whether, for example, laser surgery is an alternative to glasses and contact lenses.
The yellow spot
On the retina of the eye is the so-called focal point, also called the “yellow spot” or fovea centralis. This is exactly where the light rays ideally strike through the lens – you see everything sharply. Almost every second German, however, has limited vision, is short-sighted or long-sighted. The lens of the eye cannot adjust properly from near to far vision – or vice versa.
Nearsightedness and astigmatism
Anyone who has trouble seeing at a distance suffers from nearsightedness, also called myopia. The cause is usually a too long eyeball or too strong refractive power of the cornea: here the light rays meet in front of the retina, therefore no sharp image can be formed on the retina. Distant objects are recognized less well than near ones. It is noticeable that nearsighted people often squint their eyes. This makes the palpebral fissure narrower and the pupil diameter smaller, and only the central ray path can be transmitted. There are two types of myopia:
- The so-called school myopia (myopia simplex), which occurs between the ages of ten and twelve. It comes to a halt around the age of 25.
- Progressive myopia (myopia progressiva), on the other hand, becomes progressively worse and it is not uncommon for the patient to have severe visual impairment up to -15 diopters and more. Also, the retina is strongly stretched, sometimes it even detaches.
What is a diopter?
The physical unit diopter refers to the refractive power of an optical lens, for example, the eye. If the eye is nearsighted, the diopter values are preceded by a minus sign (-). If the eye is farsighted, the values are indicated with a plus sign (+).
Astigmatism
In addition to myopia, astigmatism, also called astigmatism, often exists. It results from an uneven curvature of the corneal surface. Like the lens of a photographic camera, the normal cornea is hemispherical. Therefore, vertical as well as horizontal lines are sharply imaged. If the cornea is not hemispherical, but rather elliptical, the image is distorted. A point is not imaged as a dot, but as a small line.
Farsightedness
In farsightedness, experts also call it hyperopia or hypermetropia, the eyeball is a little too short, sometimes the refractive power of the eyes is also too low. When looking at an object up close, the farsighted eye does not succeed in focusing the light strongly enough. The refractive power of the eye is not sufficient, the sharp image is only formed behind the focal point. On the retina, only a blurred image is formed. Light reaching the eye from a distance, on the other hand, can be focused normally. As soon as you get closer to people or objects, the image that was still sharp in the distance becomes blurred. With farsightedness, eye pain and headaches are the most common complaints. This is related to the constant strain on the ciliary muscle: Namely, the ciliary muscle controls the elongation of the lens, which alters the refractive power. This is compounded by rapid eye fatigue or blurred vision.
Presbyopia
As people age, many feel that their arms have become too short when reading – the letters blur close to the eye. Presbyopia, or presbyopia, occurs when the elasticity of the lens decreases. From around the age of 40 to 45, the lens and the ring muscle in the eye lose their elasticity, and focusing becomes imprecise. Reading glasses are now inevitable.
Alternative to contact lenses and glasses: laser surgery.
Contact lenses and glasses temporarily compensate for defective vision by reducing or increasing the refractive power of the eye by advancing the appropriate correction value. However, nearsightedness and farsightedness can be corrected under certain conditions with the help of so-called refractive eye surgery by changing the refractive power of the eye by a certain amount.Refractive procedures are various procedures for the surgical correction of refractive errors such as nearsightedness, farsightedness and astigmatism. Ophthalmologists have been using laser technology to treat refractive errors since the early 1960s. Photorefractive keratectomy (PRK) is a laser procedure used to abrade the cornea. The center of the cornea is about 0.5 mm thick, its edge about 1 mm. By means of the laser, a part of the central cornea approximately 0.1 mm thick is now ground off in order to compensate for the defective vision. A disadvantage of PRK is the slow healing and the sometimes significant pain after the operation.
The LASIK method
In 1993, however, the breakthrough came with the invention of the so-called LASIK technique – an abbreviation for laser in situ keratomileusis – in German “laser ablation inside the corneal tissue” – probably the most widely used laser technique today. Well over 100,000 patients in Germany undergo surgery using this method every year; the success rate depends on the dioptric number. The lower the number, the higher the success rate. In general, the success rate is between 97 and 99 percent. It is scientifically recognized and, according to Dr. Martin vom Busch, senior physician at the Euro Eye Laser Clinic (private clinic for laser eye surgery) in Fürth, classified as a suitable surgical correction procedure for people suffering from nearsightedness up to -10 diopters or astigmatism up to 3 diopters and farsightedness up to + 3 diopters – but presbyopia cannot be improved in this way.
Procedure during surgery
Under local anesthesia, the cornea of the eye is cut flat. This allows the upper, curved piece of the cornea to be folded back like a small lid. This is where the laser work begins:
The excimer laser is a cold-light laser in the invisible ultraviolet spectrum that penetrates and ablates just a few thousandths of a millimeter of corneal tissue – all done under computer control. The corneal flap is then closed again and the corneal flap protects the resulting wound like a natural plaster, allowing it to heal undisturbed. The entire operation takes a maximum of ten minutes. However, health insurance companies pay the rather high costs of about 2,000 euros per eye only in exceptional cases. However, laser correction should generally be discouraged if the patient is under 18 years of age, if the refractive error keeps changing significantly, in cases of cataracts and chronic corneal diseases as well as systemic immune diseases.
Lens surgery
The lens of the eye can also be operated on (without laser) – for example, about 800,000 patients are treated annually in Germany for cataracts, a clouding of the lens of the eye usually from the age of 60. Here, the cloudy lens of the eye is removed and replaced by an artificial clear eye lens. The implantable contact lens is an alternative for high refractive errors, i.e. myopia from -10 to -20 diopters and hyperopia from +5 to +8 diopters. It can be considered especially when the cornea is too thin. A special artificial lens is placed inside the eye, between the iris and the eye lens, in the so-called posterior chamber. The eye’s own lens continues to retain its ability to see close up. The cornea usually remains untouched during this procedure. Long-term experience with this surgical method is still lacking. In about 90 percent of cases, it should be possible to live everyday life without glasses. These results are sometimes significantly worse with corrections of farsightedness or astigmatism. After surgery, it is necessary to take eye drops for several months to prevent scarring of the cornea.