Refractive surgery

from Wikipedia, the free encyclopedia

The generic term refractive surgery are eye surgeries summarizes which the total refractive power change of the eye and so conventional optical corrections such as glasses or contact lenses to replace or at least to significantly reduce their required strength. The ophthalmology knows several surgical techniques for the correction of ametropia that vary depending on accurate dosing, durability and possible side effects may differ.

history

The excimer laser with which I. Pallikaris performed the first LASIK treatments

Glasses have been used to correct poor eyesight since the 13th century. Refractive surgery began in the early 20th century. The first clinical studies to investigate surgical methods for "modeling" the cornea began in the 1930s with experiments on radial (also: radial) keratotomy (RK). Up to sixteen radial or star-shaped cuts in the surface of the cornea should flatten them by means of destabilization and enlarge their radius of curvature in order to correct myopia. However, corneal scarring complications with this procedure. It was not until 1978 that radial keratotomy was increasingly used in nearsighted people and mainly in the Soviet Union and the USA with initial success.

The pioneer in the field of radial keratotomy at that time was the Russian ophthalmologist Svyatoslaw Fjodorow , who had his patients operated on an assembly line by trained specialists in ten work steps . The initially impressive successes were put into perspective in the USA by the so-called PERK study. Among other things, this demonstrated, in addition to a significant medium-term decrease in the effect of the operation, also poor predictability and thus ensured that the radial keratotomy became less important.

Instead of flattening the cornea by directly weakening the cornea with deep incisions, the Spaniard Jose Iganacio Barraquer has been pursuing the flattening by removing tissue from the inner corneal layers (keratomileusis) since 1963.

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

In Germany, 0.2% of the population had their visual defects treated with refractive surgery (as of 2004). 25,000–124,000 operations are performed each year (depending on the source), and the number is rising. An outpatient operation to correct ametropia currently costs 1,000–2,000 euros per eye in Germany and, in accordance with the guidelines of the Federal Committee of Doctors and Health Insurance Funds of December 10, 1999, may not be covered by statutory health insurance (there are a few exceptions, such as B. the lens exchange with existing lens opacity).

functionality

Schematic overview of normal vision and axial refractive errors

An axial refractive visual defect is when the focal length of the optical system of the eye does not match the length of the eyeball. If the eyeball is too long in relation to the refractive power of the eye, it is called nearsightedness or myopia. Too short an eyeball leads to farsightedness or hyperopia. Astigmatism , astigmatism or astigmatism occur when the optical system of the eye has different focal points in different meridians. The extent of ametropia is given in diopters . Myopia need diverging lenses with negative refractive power and farsighted convergent lenses with positive refractive power.

The aim of all refractive surgical operations is to adjust the total refractive power of the optical system of the eye so that the environment is sharply depicted on the retina. This can be done by changing the refractive power of the cornea (e.g. laser procedures such as LASIK or PRK, astigmatic keratotomy) or by implanting an additional or replacing the body's own lens. The refractive power of the cornea is changed by changing its curvature, either by removing tissue (laser process) or by means of defined incisions which, essentially due to the intraocular pressure , bring about a change in shape. In the nearsighted eye, a flattening, i.e. a reduction in the refractive power, is necessary, and in the farsighted eye, a steepening, i.e. an increase in the refractive power is necessary. Lens implants (so-called intraocular lenses ) are practically implanted spectacle lenses that are selected depending on the correction required. There are implants that are used in addition to the body's own lens (usually in the anterior chamber of the eye), and those that replace the body's healthy lens. The correction of the refractive visual defect as part of a cataract operation (i.e. the replacement of the clouded lens with an implant) is not considered refractive surgery, however. Although there are various methods of changing the refractive power of the eye, laser methods for low to medium corrections and intraocular lenses for high corrections have become established.

After all these methods have been successfully applied, the focal point of parallel incident light of the non-accommodated optical system of the eye is again on the retina. However, this does not mean that so-called presbyopia , or presbyopia , can be corrected with these procedures. Presbyopia means that the accommodation of the eye, i.e. the ability to focus on objects at different distances, is restricted. Unfortunately, this dynamic process of the body's own lens cannot yet be restored therapeutically. There are, however, ways to achieve an acceptably sharp local and television view. This can be done by two basic principles. On the one hand, the different refractive correction of both eyes, whereby one eye is corrected for near and one eye for far (so-called monovision ). On the other hand, through multifocality, i. That is, within the optical opening of the eye there are zones with different refractive power. This can be achieved through intraocular lenses or special laser treatments. The disadvantage of both principles is usually poor quality of vision in all distance ranges.

Laser process

Excimer laser for refractive surgery

Tissue ablation to change the corneal curvature using a laser can be done in two ways. The method, which has been used since 1987, evaporates the tissue to be ablated through an effect called photoablation . The excimer laser , which is mainly used for this, works with a wavelength of 193 nm, but solid-state lasers with a wavelength of 213 nm are also used. This ultraviolet light is immediately absorbed by the corneal tissue, and if the energy and duration of the pulse are chosen correctly, photoablation occurs. This allows a very precise and gentle tissue ablation, since the ablated tissue volume is identical with each laser pulse and the surrounding tissue is almost not heated. The tissue ablation can thus be precisely defined by the number and arrangement of the laser pulses.

The ablation profile, i.e. the exact shape and size of the tissue to be ablated, essentially depends on the type and level of correction and the treatment diameter. The shape of the tissue to be removed resembles a lens, and the thickness of this lens, i.e. the depth of the maximum removal, can be determined with the help of the so-called Munnerlyn formula :

  • = Removal depth in µm
  • = Diameter of the treatment in mm
  • = Correction in diopters

As you can see, both the desired correction and the treatment zone have an influence on the amount of tissue to be removed. The treatment zone should be at least as large as the pupil diameter under mesopic conditions (twilight). If the zone is chosen too small, distracting optical effects can occur with dilated pupils (twilight, darkness). These effects are caused by the sudden change in the refractive power at the edge of the treatment area. In order to prevent this effect, modern laser devices add a transition zone to the actual treatment zone, which is intended to ensure a smooth transition of the refractive power.

In addition to these corrections of the sphero-cylindrical visual defect, there is the possibility of correcting irregular optical defects with the help of topography- or wavefront-controlled laser treatments. For this purpose, images are first made with the corneal topograph and / or wavefront aberrometer , depending on the indication . A software calculates the exact ablation profile from these recordings, which is then removed by the laser.

A newer laser method for removing corneal tissue, which has been in use since 2007, uses a femtosecond laser , i.e. a laser with ultrashort light pulses that works at a wavelength of 1043 nm. In this procedure, called " femtosecond lenticle extraction ", the tissue is not vaporized but cut out. The cut with such a laser is made by lining up tiny cavitation bubbles in the tissue. These bubbles are created in the focus of the laser because the necessary energy density is achieved there. Because the unfocused laser is hardly absorbed by the corneal tissue, the cuts can be made at any depth in the cornea.

The shape and size of the lenticular corneal tissue cut out in this way, known as the lenticle, is based on the same parameters that also apply to treatment with the excimer laser.

Implants

Phakic intraocular lens

Artificial lenses (also called intraocular lenses ) made of various biocompatible materials (today mostly acrylic or silicone) can be implanted in the eye and thereby change its overall refractive power.

There are different procedures:

1. Supplementing the natural lens with an additional artificial lens. This can

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

can be used.

2. Replacement of the body's own lens with an artificial lens

  • with a clear natural lens: refractive lens exchange
  • for a naturally cloudy lens: cataract surgery

3. Using an implant in the cornea

The first-mentioned additionally introduced lenses are called phakic lenses because the body's own lens ( Greek φακός phakos ) 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 differentiated according to the type of attachment in the eye in lenses fixed at the chamber angle or iris.

Another method or aid is the KAMRA implant , a black lens with a small hole in the middle, which is used for the surgical correction of presbyopia according to the principle of the Stenopean gap and is implanted under the cornea.

chances and risks

Refractive surgery offers the chance to significantly reduce the patient's visual defects within certain limits. In the best case, the remaining refraction is less than ± 0.5 dioptres and the patient no longer needs any visual aids (glasses, contact lenses). The raw visus , d. H. unaided visual acuity usually improves dramatically, ideally reaching 1.0 or more. The best corrected visual acuity (visual acuity with optimal eyeglass correction), on the other hand, remains mostly unchanged or changes slightly (depending on the treatment method). The expectations of the surgical result are very individual and vary from patient to patient. They should be discussed in detail with the treating doctor in advance.

As with any surgical procedure, there are a number of risks associated with refractive surgery. The type and frequency of complications also depend on the treatment method. However, the surgeon's experience, the level of correction, the technique used and the patient's individual dispositions also play an important role. It should also be borne in mind that refractive surgery is, in principle, a surgical procedure on a normally healthy organ.

General risks associated with any type of refractive surgery are limitations in twilight and night vision due to reduced contrast sensitivity, glare (glossy effects) and halogons (halos). Short-term to long-term over- or undercorrections as well as a reduction in visual acuity with optimal glasses correction (so-called best-corrected visual acuity) can also occur. Infections of the eye are possible with any type of treatment, but especially with implants.

The risk of visual impairment after laser treatment also depends on individual risk factors (such as the number of diopters, flat cornea, pupil size). In addition, the surgeon's experience has a serious influence on the complication rate. A study from 1998 compared the intraoperative complication rate of the first 200 treatments by a surgeon with that of the following 4800 treatments. The rate for the first 200 treatments is 4.5%, and only 0.87% for the subsequent treatments.

A very serious risk is the structural weakening of the cornea after tissue removal. This weakening and the constant intraocular pressure acting on the cornea can lead to a bulging of the cornea ( keratectasia ). The risk of this increases as the remaining thickness of the cornea decreases after the treatment. The minimum value for the remaining thickness is 250 µm. The remaining thickness is calculated from the central corneal thickness minus the flap thickness and the central tissue removal. Genetic factors also seem to play a role in keratectasia.

Methods

Laser process

The vast majority of refractive treatments are performed with the help of lasers. Good predictability and relatively low side effects have made these methods the method of choice. They are particularly suitable for small to medium corrections up to a maximum of around −10 dioptres.

LASIK

LASIK ( laser in situ keratomileusis ) is currently the most popular method for refractive surgery. With a microkeratome (corneal plane) or a femtosecond laser (so-called Femto-LASIK) a thin lamella (diameter approx. 8 to 9.5 mm and thickness between 100 and 160 µm) is cut into the cornea. This lamella is opened and the actual laser treatment takes place on the underlying tissue. The duration of the laser irradiation depends on the amount of correction and the treatment diameter, but with modern lasers it is usually less than 30 s.

A LASIK patient has sharp vision very quickly and relatively painlessly, as the operation is carried out under the pain-sensitive corneal surface and , in contrast to surface treatments (PRK, LASEK, EpiLASIK), the epithelium does not have to grow back. However, the operation-related corneal incision (flap) results in a higher risk potential for various complications. Especially in the first few weeks, dry eyes, foreign body sensations and nocturnal glare effects can occur, but the symptoms usually disappear. In addition to possible flap complications, long-term complications such as post-LASIK keratectasia with a latency period of up to 10 years can also occur. The frequency of this severe, visually impairing complication is given as around 0.6% and 0.9% or up to 2.5% for higher myopia.

The LASIK method is indicated for corrections in the range of +4 to −10 diopters.

PRK, LASEK and EPILASIK

In the laser procedures photorefractive keratectomy (PRK), laser epithelial keratomileusis (LASEK) and epithelial laser in situ keratomileusis (EpiLASIK), tissue is removed from the corneal surface. They are therefore also referred to as surface ablation . PRK is the oldest laser procedure for the treatment of ametropia and has been used since 1987. In all three methods, the epithelium is first removed in a sufficiently large (8-10 mm diameter), central corneal area and then the corneal surface is treated with the laser. The procedures differ in how the epithelium is removed and what happens to it after treatment. In PRK, the epithelium is scraped off with the help of a surgical instrument and not used again. The LASEK and EpiLASIK procedures use the epithelium as a natural wound dressing after treatment. With LASEK, the epithelium is loosened with alcohol and pushed aside with a suitable instrument, with EpiLASIK, however, it is lifted off with a blunt corneal plane similar to a microkeratome and forms a kind of epithelial flap. In all three procedures, the epithelium must regenerate after treatment. A few days pass before complete regeneration, during which the eye can hurt and also not yet optimal visual acuity. The maximum treatment range for these procedures is +4 to −8 diopters.

Femtosecond Lenticle Extraction

Femtosecond lenticular extraction is a relatively new technique. As with the PRK and LASIK excimer laser procedures, the ametropia is corrected by changing the corneal curvature. In contrast to the aforementioned methods, however, this is not achieved by vaporizing corneal tissue. With the help of a femtosecond laser , a so-called lenticle is cut within the cornea. This lenticular piece of tissue is then removed and the resulting change in corneal curvature corrects the ametropia. Depending on how this lenticule is removed, a distinction is made between two procedures. With the method called FLEx ( Femtosecond Lenticle Extraction ), not only the lenticle is cut during the laser treatment, but also a lamella (flap) above it. This flap is then opened and allows the lenticle to be removed. In the second, SmILE ( English Small Incision Lenticle Extraction ) method called intersects the laser not complete flap, but only a small, peripheral incision can remove the lenticule by the doctor. Femtosecond lenticule extraction is indicated for the correction of myopia up to −10 diopters and astigmatism up to 3 diopters.

Implants

The correction of the refractive visual defect is carried out by inserting implants in different parts of the eye. In principle, one can differentiate between two types of implants . The most commonly used implants are inserted into the beam path of the eye and correct the visual defect with their own refractive power ( intraocular lenses ). However, there are also implants that are inserted into the peripheral cornea and thereby cause a change in the shape of the cornea ( intrastromal corneal ring segment ).

Phakic intraocular lenses

One method to correct higher visual defects is the implantation of phakic intraocular lenses . These are artificial lenses that are implanted in the eye in addition to the body's own lens. Depending on the lens type, the artificial lens is in the front (between cornea and iris ) or in the rear (between the iris and lens of the eye ) ocular chamber introduced Alternatively, the natural lens can be replaced by an artificial lens.

The procedures mentioned are suitable for myopias from −5 dioptres and hyperopias from +3 dioptres. In the case of minor ametropia, laser procedures are preferable.

CISIS

A small, closed 360 ° full ring (SehRing, MyoRing) is pushed 0.3 mm below the corneal surface into the cornea. This procedure is known as CISIS (Corneal Intrastromal Implantation Surgery) and is said to be particularly effective for moderate and high myopia from −8 D and for keratoconus . The manufacturer describes the procedure, which has been approved since 2007, as safe, because the ring is placed in a corneal pocket and the cornea is therefore not weakened as with LASIK. The treatment should be completely reversible and the eye ring should be easy to remove or replace if necessary. A protrusion (keratectasia) of the cornea, a possible complication after LASIK, should also be able to be corrected with the implant. Independent studies on the correction of myopia, especially on long-term effects, are not yet available. In addition, CISIS is not a generally established standard procedure.

Proof of quality

The objective proof of quality is very important for patients. There are various certificates that are used in healthcare.

QM certificate according to ISO 9001: 2008

The ISO 9001: 2000 certificate is a purely process-oriented quality management seal that is awarded across all industries. It reflects process quality and says nothing about the quality of the medical treatment or the technical status of the instruments used.

LASIK TÜV

Between 2006 and 2017 there was the so-called LASIK TÜV especially for laser eye centers, which was based on the ISO 9001: 2000 certificate. It was offered by TÜV Süd and developed in cooperation with the Refractive Surgery Commission (KRC), the Association of Special Clinics for Laser Eye and Refractive Surgery (VSDAR eV) and the Professional Association of Ophthalmic Surgeons (BDOC). In contrast to the ISO-9001: 2000 certificate, the LASIK-TÜV not only checked the process quality, but also the quality of service and results. The following aspects were specifically examined:

  1. Qualifications and experience of employees and doctors,
  2. technical equipment of the facility,
  3. Facility hygiene standards,
  4. Treatment results,
  5. Patient satisfaction.

The issuing of TÜV certificates for LASIK providers was discontinued in January 2017. Since then, the corresponding test marks may no longer be used by the clinics.

See also

literature

  • Theo Seiler (Ed.): Refractive surgery of the cornea. Enke im Thieme Verlag, Stuttgart a. a. 2000, ISBN 3-13-118071-4 .
  • Berthold Graf: A life without glasses and contact lenses - eye lasers and other alternatives. Baltic Sea Press, Rostock 2009, ISBN 978-3-942129-14-5 .
  • Thomas Kohnen (Ed.): Refractive Surgery. Springer, Berlin 2011, ISBN 978-3-642-05405-1 .

Web links

Individual evidence

  1. ↑ SL Trokel, R. Srinivasan, B. Braren: Excimer laser surgery of the cornea . In: American Journal of Ophthalmology . tape 96 , no. 6 , November 1983, p. 710-715 , PMID 6660257 .
  2. ↑ Dimitri T. Azar, Sandeep Jain, Robert Edward Ang: LASEK, PRK, and excimer laser stromal surface ablation . Marcel Dekker, 2004, ISBN 0-8247-5434-4 , p. 2 , Table 1. Milestones in LASEK History .
  3. ↑ Loannis G. Pallikaris, Maria E. Papatzanaki, Evdoxia Z. Stathi, Oliver Frenschock, Anthimos Georgiadis: Laser in situ keratomileusis . In: Lasers in Surgery and Medicine . tape 10 , no. 5 , 1990, pp. 463-468 , doi : 10.1002 / lsm.1900100511 .
  4. ↑ Guidelines on new examination and treatment methods (NUB guidelines) . In: Deutsches Ärzteblatt . tape 97 , no. 13 , 2000, pp. A-864 ( aerzteblatt.de [PDF]).
  5. ↑ a b c d Thomas Kohnen, Anja Strenger, Oliver K. Klaproth: Basic knowledge of refractive surgery. Correction of refractive errors with modern surgical procedures. In: Deutsches Ärzteblatt . tape 105 , no. 9 , February 29, 2008, p. 163–172 , doi : 10.3238 / arztebl.2008.0163 ( aerzteblatt.de [PDF]).
  6. ↑ Professional Association of Ophthalmologists in Germany e. V., German Ophthalmological Society [DOG] (Hrsg.): Operations to eliminate ametropia . 2008 ( dog.org [PDF; 118 kB ]).
  7. ↑ Walter Sekundo : Femtosecond Lenticular Extraction. This investigational new procedure is unique to the VisuMax laser, and currently only performed by two clinical investigators in Germany. In: Cataract & Refractive Surgery Today Europe . No. 4 , 2007, p. 72-73 ( crstodayeurope.com ).
  8. ↑ Simulator for twilight and night vision according to LASIK depending on the number of diopters and pupil diameter . April 28, 2010.
  9. ^ Mihai Pop, Yves Payette: Risk Factors for Night Vision Complaints after LASIK for Myopia. (PDF) In: Ophthalmology. 111, 2004, pp. 3-10
  10. ↑ Individual risk factors for halos, loss of contrast, glare, starburst after LASIK . operationauge.de, March 11, 2010.
  11. ↑ JS Vidaurri-Leal: Complications in 5000 LASIK procedures . In: Group RSSI, ed. Refractive Surgery . 1998, p. 61-64 .
  12. ↑ Lasik or Lasek - the laser correction
  13. ^ PS Binder: Analysis of ectasia after laser in situ keratomileusis: risk factors. In: Journal of Cataract and Refractive Surgery . 2007; 33, pp. 1530-1538.
  14. ↑ L. Spadea et al. a .: Corneal Crosslinking for Keratectasia after Laser in Situ Keratomileusis: A Review of the Literature. In: J Kerat Ect Cor Dis. 2013; 2, pp. 113-120.
  15. ↑ JL Alio et al. a .: Laser in situ keratomileusis for -6.00 to -18.00 dioptres of myopia and up to -5.00 dioptres of astigmatism: 15-years follow-up. In: Journal of Cataract and Refractive Surgery. 2015; 41, pp. 33-40.
  16. ↑ a b Brief overview of the methods of refractive surgery. Refractive Surgery Commission (KRC), 2010, archived from the original on March 4, 2016 ; Retrieved November 3, 2010 .
  17. ↑ Refractive Lenticle Extraction (ReLEx). (No longer available online.) University Hospital Gießen and Marburg, July 10, 2010, archived from the original on October 18, 2010 ; Retrieved November 3, 2010 .
  18. ↑ Anterior versus Posterior Phakic IOLs: What is the best lens? Retrieved February 23, 2010 .
  19. ↑ A. Daxer: Corneal intrastromal implantation surgery for the treatment of moderate and high myopia. In: J Cataract Refract Surg. 2008; 34, pp. 194-198.
  20. ↑ M. Jabbarvand et al. a .: Femtosecond Laser-Assisted MyoRing Implantation in Postoperative LASIK Ectasia. In: J Refract Surg. 2014.
  21. ↑ List of certified clinics. TÜV Süd, accessed on May 16, 2012 .
  22. ↑ The LASIK TÜV seal of approval. Archived from the original on March 6, 2010 ; Retrieved March 3, 2010 .
  23. ↑ The LASIK-TÜV SÜD standard has been discontinued . MOT South