Corneal surgery
A small change in the curvature of the cornea has a great effect since the cornea is responsible for a large proportion of the refractive power of the eye. In the case of nearsightedness the refractive power is reduced by a flattening in the center of the cornea. The light rays are refracted less strongly and are once again focussed sharply on the retina. In the case of farsightedness, the center is raised. The light rays are refracted more strongly and directed again to the retina. In the case of astigmatism, the irregular curvature of the cornea is compensated for. The surface once again more closely approaches the ideal ball shape.
Corneal surgery procedures
- Laser techniques
- Cutting techniques
- Corneal implants
Laser techniques:
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Excimer laser
The excimer laser penetrates just a few thousandths of a millimeter into the cornea. It therefore enables layers of corneal tissue to removed with great accuracy. The laser operates in the invisible ultraviolet spectrum (wavelength: 193 mm). In the vast majority of cases vision without glasses or contact lenses is considerably better than before the treatment.
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Photorefractive keratectomy (PRK)
In this procedure the computer-controlled excimer laser is used to change the refractive power of the central cornea. The procedure is restricted to the surface of the cornea. Here a very thin layer of corneal tissue is removed from the center of the cornea. Experience with the excimer laser dates back to 1986. PRK is routinely used for the correction of slight to moderate nearsightedness (approx. -2 to -6 diopters) and with moderate astigmatism (up to about -3 diopters). PRK can also serve as a useful therapeutic operation for surface scarring or pathological changes of the cornea. It is then known as PTK (phototherapeutic keratectomy).
Pain may be experienced in the first days after the PRK but this can be treated with drugs. Since 1993, PRK has been accepted by the German Ophthalmological Society (DOG) and the German Professional Association of Ophthalmologists (BVA) as a secondary alternative to glasses and contact lenses for the correction of nearsightedness up to -6 diopters. The PRK procedure is regarded as safe and reliable for defective vision up to -6 diopters. As yet there is no long-term experience dating back over several decades.
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Laser in situ keratomileusis (LASIK)
For the correction of more severe vision problems (-6 to -10 diopters) the combination of the excimer laser technique (PRK) with a cutting technique (keratomileusis) has proved advantageous. Here the actual refraction-changing laser intervention is transferred to the inside of the cornea. With LASIK a thin flap of corneal surface is cut and laid back using an automatic knife (microkeratome). The surgeon then uses an excimer laser to remove a lower layer of corneal tissue. Following this laser treatment the corneal flap is replaced. The corneal flap does not require stitching because it is once again resting on the lower cornea. The corneal flap thus acts as a protective cover over the resulting wound. As a general rule, patients only experience slight pain following this operation. The LASIK procedure has been used since 1991. Investigations thus far have shown good results in treating nearsightedness of up to about -10 diopters, farsightedness up to about +4 diopters and an astigmatism of more than -2 diopters.
LASIK is scientifically approved by the Committee of the Professional Association of Ophthalmologists (Refractive Surgery Committee) for the treatment of nearsightedness of around -6 diopters to around -10 diopters..
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Laser thermal keratoplasty (LTK)
The use of a holmium laser, which functions in the infra red range (wavelength approx. 2.1 µm), enables farsightedness to be treated using the LTK technique. The heat effect of this laser beam causes scarring of the corneal tissue. The laser sources are applied to the edge of the cornea in the shape of a circle leading to a shrinking of the affected central corneal layers. The result is greater curvature in the untreated central corneal region which can compensate for an existing farsightedness within certain limits. Slight farsightedness and minor over-corrections, such as after PRK for example, can be treated with LTK. However the effect of this treatment decreases over time. Because the treatment results do not conform with our quality criteria, LTK is not used in our clinic.
Surgery with a diamond knife:
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Astigmatic keratotomy (AK)
AK originates from the so-called radial keratotomy (RK) of Professor Fjodorov from Moscow. AK is the operative treatment of astigmatism with a diamond knife. It involves precise cuts in the cornea positioned in such a way as to flatten the area of greater curvature. AK enables more severe cases of astigmatism in excess of -5 diopters to be treated. This procedure is particularly suitable in cases of acquired astigmatism.
