Refractive surgery

Under the generic term refractive surgery eye surgeries are combined, the overall change in refractive power of the eye and replace as conventional optical corrections such as glasses or contact lenses, or at least to reduce their required strength significantly. Ophthalmology knows several surgical methods for the correction of ametropia, which may differ durability and possible side effects with regard to accurate dosing.

• 4.1 Laser Procedures 4.1.1 LASIK
• 4.1.2 PRK, LASEK and EpiLASIK
• 4.1.3 Femtosecond lenticule extraction

• Phakic intraocular lenses 4.2.1

• 5.1 QM certificate according to ISO 9001:2008
• 5.2 LASIK -TÜV

History

Since the 13th century eyeglasses are used to correct poor eyesight. The refractive surgery began in the early 20th century. The first clinical studies investigating surgical methods for the " modeling " of the cornea began in the 1930s with experiments on the radial (also: radial ) keratotomy (RK ). Up to sixteen radial or star- shaped cuts into the surface of the cornea (cornea ) this should flatten by destabilization and increase their radius of curvature to correct myopia. However, in this method were complications by scarring of the cornea. It was not until 1978, radial keratotomy has been used increasingly in short-sighted people, mainly in the Soviet Union and the United States with initial success.

Pioneer in the field of radial keratotomy was at that time the Russian Svyatoslav Fyodorov eye doctor, who had surgery on an assembly line by trained staff his patients in ten steps. The initial impressive successes have been relativized in the United States by the so-called PERK study. These and among other things, in addition to a significant medium-term decline of the operation effect and a lack of predictability after and made so that the radial keratotomy lost its importance.

Rather than perform the flattening by a direct weakening of the cornea with deep cuts, the Spaniard Jose Barraquer Iganacio has been since 1963 the flat -surface tissue ablation by the inner layers of the cornea Following ( keratomileusis ).

Trokel Stephen et al. described in 1983 as first the method of refractive correction with an excimer laser. 1987 was first used on humans by Theo Seiler at the University Hospital of the Free University of Berlin with photorefractive keratectomy (PRK ) this procedure. In the 1990s, the PRC has been further developed for LASEK. 1989 keratomileusis were combined for the first time with the Excimerlaserverfahren and Pallikaris et al. described as laser in situ keratomileusis (LASIK ). These laser procedures are used today mainly and have other methods, such as radial keratotomy largely displaced.

In Germany, 0.2 % of the population who treat their visual defects by means of refractive surgery can (as of 2004). 25000-124000 operations are performed ( depending on the source ), and rising every year. Outpatient surgery for the correction of ametropia currently costs in Germany 1000-2000 euros per eye and must not be taken over by the statutory health insurance of 10 December 1999 in accordance with the guidelines of the Federal Committee of Physicians and Sickness Funds ( There are a few exceptions, such as the lens replacement in existing lens opacities ).

Operation

From an axial refractive vision errors is when the focal length of the optical system of the eye does not coincide with the length of the eyeball. If the eyeball in relation to the eye refractive power too long, it is called nearsightedness or myopia. A too short eyeball leads to farsightedness or hyperopia. Astigmatism, corneal irregularity or astigmatism occurs when the optical system of the eye has different focal points in different meridians. The extent of ametropia is expressed in diopters. Short-sighted need diverging lenses with negative refractive power and far-sighted collector lenses with positive refractive power.

The objective of all refractive surgical operations is the total refractive power of the optical system of the eye to adapt so that the environment is imaged sharply on the retina. This can be done by changing the refractive power of the cornea (for example, laser processing such as LASIK or PRK, astigmatic keratotomy ) or by implantation of a supplementary or replacement of the natural lens. The change in refractive power of the cornea is done by changing its curvature, either by tissue ablation (laser procedure) or by defined incisions, mainly due to the intraocular pressure to bring about a change in shape. In the myopic eye is a flattening, ie reducing power, and the farsighted a steepening, ie power increase is necessary. Lens implants ( intraocular lenses ) are practically implanted lenses, which are selected depending on the required correction. There are implants that are used in addition to the natural lens (usually in the anterior chamber ) and those that replaced the healthy natural lens. Correction of refractive visual error in a cataract operation ( ie replacing the clouded lens with an implant ) is however not considered refractive surgery. Although there are various methods for change in refractive power of the eye to laser procedures for low to medium corrections and intraocular lenses for high corrections have prevailed.

After a successful application of this method all the focal point parallel to the incident light of the optical system of the unaccommodated eye has returned to the retina. However, this does not mean that the so-called presbyopia, or presbyopia, can be corrected with this method. Presbyopia means that the accommodation of the eye, ie the ability to focusing at different distant objects is limited. Unfortunately, this dynamic process of the body's lens can not therapeutic yet to be restored. However, there are ways to achieve an acceptably sharp close-up and television. This may be accomplished by two basic principles. Firstly, the different refractive correction in both eyes, one eye for near and one eye is corrected for far (so-called monovision ). Secondly by multifocality, i.e., within the optical aperture of the eye, there are zones of different refractive power. This can be achieved by intraocular lenses or laser special treatments. Disadvantage of the two principles is generally a poorer quality of vision at all distances.

Laser method

The tissue removal to change the corneal curvature by laser can be done in two ways. The applied since 1987 method vaporizes the tissue to be ablated by an effect which is called photoablation. The predominantly used for excimer laser operating at a wavelength of 193 nm, but also solid-state laser with a wavelength of 213 nm are used. This ultraviolet light is absorbed immediately by the corneal tissue, and if the energy and duration of the pulse are correctly chosen, it is for photoablation. This allows a very precise and gentle tissue removal, since the ablated tissue volume is the same for each laser pulse and Surrounding tissue is almost not heated. Can be precisely defined by the number and arrangement of the laser pulses thus the tissue removal.

The ablation, so the exact shape and size of the tissue to be ablated, depends essentially on the type and amount of correction and the treatment diameter. The shape of the tissue to be ablated is like a lens, and with the help of the so-called Munnerlyn formula, the thickness of this lens, so the depth of the maximum material removal rate, determine:

• = Excavation depth in microns
• = Diameter of the treatment in mm
• = Correction in diopters

As is seen, both the desired correction and the treatment zone have an influence on the amount of tissue to be ablated. The treatment area should be at least as large as the pupil diameter under mesopic conditions ( twilight ). If the zone is too small, it can cause disturbing visual effects with dilated pupils ( twilight, darkness). These effects are caused by the sudden change of the power at the edge of the treatment zone. To prevent this effect, add modern laser devices the actual treatment zone, add a transition zone to ensure a smooth transition of power.

In addition to these corrections, the sphero - cylindrical refractive error is possible, irregular optical errors with the help of topography or wavefront- controlled laser treatments to correct. These recordings with the diagnostic equipment Hornhauttopograf and / or wavefront aberrometer be made depending on the indication first. A software calculated from these recordings the exact ablation, which is then removed from the laser.

A more recent, Applied since 2007, laser method for removing the corneal tissue using a femtosecond laser, ie a laser having ultra-short pulses of light, which operates at a wavelength of 1043 nm. In this, "Femtosecond lenticule " mentioned method, the tissue is not vaporized, but excised. The interface with such a laser is carried out by the succession of tiny cavitation bubbles in the tissue. These bubbles originate in the focus of the laser, since there the necessary energy density is achieved. Characterized in that the unfocused laser is hardly absorbed by the corneal tissue, the sections can be produced at any depth of the cornea.

The shape and size of the cut out as lenticular corneal tissue lenticule called, is governed by the same parameters that apply to the treatment with the excimer laser.

Implants

Artificial lenses ( also called intraocular lenses ) from various biocompatible materials ( today usually acrylic or silicone ) can be implanted into the eye, thus changing its overall power.

One can distinguish between essentially two methods:

1st supplement the natural lens with an additional artificial lens. This can

• In the anterior chamber ( between the cornea and iris)
• In the eye posterior chamber ( between the iris and lens )

Be used.

Second replacement of the natural lens with an artificial lens

• With a clear natural lens: refractive lens exchange
• With a natural cloudy lens: cataract surgery

The former additionally introduced as phakic lenses are lenses referred to as the natural lens (Greek Phakos, φακός ) remains in the eye. At the edge of the actual lens, these implants have differently designed holding devices to fix them in the eye. The anterior chamber lenses are distinguished according to the attachment type in the eye chamber angle or iris fixed lenses.

Another method or tool represents the KAMRA implant lens, a black with a small hole in the center, which uses the principle of stenopaic gap for the surgical correction of presbyopia and is implanted under the cornea.

Opportunities and risks

Refractive surgery offers the opportunity to reduce optical refractive errors of patients significantly within certain limits. In the best case, the remaining refraction is less than ± 0.5 diopters, and the patient does not require corrective lenses (glasses, contact lenses ) more. The rough visus, that is, the visual acuity without aids, improves dramatically usually achieved and ideally 1.0 or more. The best corrected visual acuity ( visual acuity with optimal spectacle correction ), however, remains ( depending on the treatment method) usually unchanged or slightly changes. The expectations of the operation result are very individual and varies from patient to patient. They should be discussed in advance in detail with the attending physician.

As with any surgical procedure, there are a number of risks, in refractive surgery. Type and frequency of complications depend also on the treatment method. However, the experience of the surgeon, the amount of correction, the technique used, and individual dispositions of the patient play an essential role. It must be remembered also that the refractive surgery is basically a surgical procedure on a generally healthy organ.

General risks with any type of refractive surgery are limitations of the twilight and night vision due to reduced contrast sensitivity, glare (specular effects) and Halo Gone ( halos ). Occurrence can also short-to long -term over-or undercorrection, and a reduction in visual acuity with optimal spectacle correction (so-called best corrected visual acuity ). Infections of the eye are possible with each type of treatment, but particularly with implants.

The risk of impairment of vision after laser treatment also depends on individual risk factors (such as the number of diopters, flat cornea, pupil size). In addition, the experience of the surgeon has a serious impact on the complication rate. A study from 1998 comparing the intraoperative complication rate of the first 200 treatments of an operator with the following 4800 treatments. In the first 200 treatments, the rate is 4.5 %, with the other treatments only at 0.87 %.

A very serious risk is the structural weakening of the cornea after Gewebsabtrag. This weakening and the constantly acting on the cornea intraocular pressure can cause a bulging of the cornea ( corneal ectasia ). The risk of this increases with decreasing residual corneal thickness after treatment. The minimum value for the residual thickness of 250 microns is. The residual thickness is calculated from the central corneal thickness minus the flap thickness and the central tissue removal. Furthermore, appear to play a role in Keratektasien genetic factors.

Methods

Laser method

The vast majority of refractive treatment is carried out with the aid of lasers. A good predictability and the relatively minor side effects have made this method of treatment of choice. They are particularly suitable for low to medium corrections to a maximum of about -10 diopters.

LASIK

LASIK (laser in - situ keratomileusis ) is currently the most popular method for refractive surgery. With a microkeratome ( Callus ) or a femtosecond laser (so-called Femto- LASIK) is a thin lamella cut (diameter about 8 to 9.5 mm and thickness between 100 to 160 microns ) in the cornea. This blade is opened and the actual laser treatment takes place on the underlying tissue. The duration of the laser irradiation is determined by the amount of correction and the treatment diameter, but is advanced lasers typically less than 30 seconds

A LASIK patient has very quick and relatively painless sharp vision, as the operation is performed under pain-sensitive corneal surface and has the epithelium in contrast to the surface treatments (PRK, LASEK, EpiLASIK ) grow, not only. Through the operation-related corneal incision (flap), however, results in a higher potential risk for various complications. Especially in the first few weeks can cause dry eyes, foreign body sensations and night glare, usually the symptoms disappear, however.

The LASIK procedure is considered indicated for corrections ranging from 4 to -10 diopters.

PRK, LASEK and EpiLASIK

With the laser photorefractive keratectomy procedure (PRK ), laser epithelial keratomileusis - ( LASEK ) and epithelial laser in situ keratomileusis ( EpiLASIK ) takes the place of tissue ablation on the corneal surface. They are therefore also called surface ablation ( engl. surface ablation ) refers. PRK is the oldest laser procedure for the treatment of refractive error and has been applied since 1987. In all three methods, the epithelium is first dissolved in a sufficiently large (8-10 mm diameter), the central area of ​​the cornea is removed and the treated surface of the cornea with the laser. The methods differ in how the epithelium is removed and what happens to it after treatment. In PRK, the epithelium is scraped away with the aid of a surgical instrument and is not used again. The method and LASEK, the epithelium EpiLASIK use as natural wound dressing after treatment. The epithelium is solubilized with LASEK with alcohol and pushed with a suitable instrument to the side, at the EpiLASIK however, it is similarly lifted with a blunt Hornhauthobel a microkeratome and forms a kind of epithelial flap. In all three methods the epithelium after treatment must regenerate. Until the complete regeneration takes a few days in which the eye can hurt and also no optimal visual acuity is achieved. The maximum treatment range for this method ranges from 4 to -8 dioptres.

Femtosecond lenticule extraction

The femtosecond lenticule extraction is a relatively new procedure and the correction of refractive errors is as for the excimer laser PRK and LASIK procedures by changing the corneal curvature. In contrast to the aforementioned method, this is not achieved by the evaporation of the corneal tissue. With the help of a so-called a femtosecond laser lenticule is cut in the cornea. This lens-shaped piece of tissue is then removed and the resulting change in the corneal curvature to correct the refractive error. Depending on how this lenticule is removed, a distinction is made between two methods. When FLEx ( Femtosecond Lenticle Extraction) method mentioned not only the lenticule is cut during the laser treatment, but also a lamella overlying (flap). This flap is then opened and allowed the removal of the lenticule. In the second, SmILE (English Small Incision Lenticle Extraction) mentioned method of laser cuts no complete flap, but only a small peripheral incision, through which the doctor can remove the lenticule. The femtosecond lenticule extraction is indicated for the correction of myopia up to -10 diopters and astigmatism up to 3 diopters.

Implants

The correction of refractive vision defect is effected by the insertion of implants in different parts of the eye. In principle, one can distinguish between two types of implants. The most commonly used implants are inserted in the optical path of the eye and correct the visual defects by their own power ( intraocular lenses ). However, there are also implants that are inserted into the peripheral cornea and thereby bring about a change in shape of the cornea ( corneal intrastromal ring segment).

Phakic intraocular lenses

A method for the correction of visual defects is higher the implantation of phakic intraocular lenses. It is artificial lenses that are in addition to the natural lens implanted in the eye. Depending on the type of lens, the artificial lens is placed in the front ( between the cornea and iris ) or the rear ( between the iris and lens ) anterior chamber Alternatively, the natural lens is replaced with an artificial lens. This lens exchange should only apply when there is already a clouding of the eye lens (cataract ).

The abovementioned methods are suitable for myopia from -5.00 diopters and hyperopia from 3.00 dpt. At lower ametropia laser procedure are preferable.

Proof of quality

The objective proof of quality is very important for patients. There are several certificates that are used in health care.

QM certificate according to ISO 9001:2008

The ISO 9001: 2000 certificate is a pure process-oriented quality management Seal, which is awarded across industries. It reflects process quality and says nothing about the quality of medical treatment or the technical status of the instruments deployed from.

LASIK -TÜV

Especially for laser eye centers there since 2006, the so-called LASIK -TÜV, which is based on the ISO 9001: 2000 certificate. It is offered by TÜV Süd and was developed in collaboration with the Commission Refractive Surgery ( KRC ), the Association of Specialty Clinics for Eye Laser and Refractive Surgery ( VSDAR eV ) and the Professional Association of Ophthalmic Surgeons ( BDOC ) was developed. In contrast to the ISO 9001: 2000 Certificate of LASIK - TÜV tests not only the process quality but also the service and quality of results. Specifically, the following aspects are examined: