Femtosecond Lenticle Extraction

from Wikipedia, the free encyclopedia

The femtosecond lenticular extraction ( FLEX ) is a method of refractive surgery , that is an eye operation , a spectacle or contact lens to correct a refractive error is to replace.

Basics

Femtosecond laser for refractive surgery

Femtosecond lenticule extraction corrects ametropia through an operation on a basically healthy organ. The aim is for the remaining refractive error to be less than ± 0.5 diopters and for the patient to manage without visual aids (glasses, contact lenses). The uncorrected visual acuity , i.e. H. The visual acuity without aids, usually improves dramatically and ideally reaches the preoperative best corrected visual acuity. 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).

As with the PRK and LASIK excimer laser procedures, the ametropia is corrected by changing the corneal curvature . The process, which has been in use since 2006, exclusively uses a femtosecond laser , i.e. a laser with ultrashort light pulses, which with a wavelength of z. B. 1043 nm works. With the help of this laser, a lens-shaped piece of tissue (the lenticle ) is formed inside the cornea . In contrast to the PRK and LASIK procedures, the correction is achieved without an odor-intensive and noisy ablation.

The cut is created by lining up tiny cavitation bubbles in the tissue. These bubbles are created in the focus of the laser beam, as the necessary energy density is only achieved there. Because the laser beam in the corneal tissue outside of the focus does not have the energy density required to generate bubbles, the bubbles and thus the cuts can be generated at any depth in the cornea. The incision is made to isolate the lenticle in the cornea. It is removed after the laser treatment, and the resulting change in the corneal curvature corrects the ametropia.

Treatment area and contraindications

As of August 2013, the procedure mentioned is indicated for the correction of:

Contraindications are circumstances that prohibit treatment or allow treatment only after careful consideration of the risks. A sufficiently thick cornea is an essential prerequisite for femtosecond lenticular extraction. Too thin a cornea is considered a strict contraindication. A remaining residual thickness of at least 250 µm after treatment is the limit. This residual thickness is calculated from the corneal thickness minus the flap thickness (if available) and the maximum lenticular thickness. Femtosecond lenticule extraction, like any other laser-assisted refraction correction, should not be performed if chronic progressive corneal disease is present. Treatment is prohibited, especially in the case of keratoconus , as the cornea is further weakened and the clinical picture would worsen dramatically. If the patient's refraction is not stable, that is, if the refraction determinations deviate significantly from one another in relatively short time intervals, femtosecond lenticle extraction should not be performed. The eye diseases glaucoma with visual field damage and symptomatic cataract continue to be considered contraindications . Common diseases that exclude femtosecond lenticular extraction are collagenoses , autoimmune diseases and wound healing disorders . Finally, patients should not be pregnant and should be at least 18 years old.

Preliminary examinations

The preliminary examinations serve on the one hand to record the correct treatment data, but on the other hand also to rule out contraindications. The patient should not wear contact lenses for at least two weeks prior to the preliminary examinations.

An essential part of the preliminary examinations is the determination of the patient's exact subjective refraction by a qualified optometrist or ophthalmologist. The refraction should be determined at least twice with an interval of at least 2 weeks. A refraction determination with an automatic refractometer is in any case insufficient!

Other important preliminary examinations are:

  • Determination of the corneal thickness with an ultrasonic pachymeter or anterior chamber OCT
  • Corneal topography for determining the corneal curvature and detection of corneal irregularities
  • Measurement of the pupil size (pupillometry)
  • Intraocular pressure measurement
  • Tear film determination
  • General ophthalmological examination including slit lamp examination
  • anamnese

Treatment process

The treatment is carried out in the following steps: The eye is anesthetized locally with drops and an eyelid retractor is used to keep the eye wide open. The eye is then brought into contact with a sterile glass surface and fixed with negative pressure. The glass surface has roughly the diameter of the cornea and serves as a laser exit window and reference surface. Immediately after fixing the eye, the laser treatment starts, which makes the necessary cuts in the cornea in one go. The laser treatment takes about 25-30 seconds, depending on the size of the treatment area. After the laser treatment, the lenticle that has just been created is removed from the cornea. There are two treatment methods that differ in how the lenticule is removed from the cornea.

In the first method, called FLEX ( Femtosecond Lenticule Extraction ), not only the lenticule but also a flap is cut during the laser treatment. This flap is then opened and allows the lenticle to be removed. After the lenticule has been removed, the flap is repositioned (FLEX) and treatment is complete.

In the second method , known as SMILE ( Small Incision Lenticule Extraction ), the laser does not cut a complete flap, but only a small 3–4 mm peripheral incision through which the doctor can remove the lenticle.

Advantages and disadvantages

Advantages of Femtosecond Lenticle Extraction:

  • Little to no pain during and after the operation
  • Very quick vision recovery - the treatment result can be experienced practically immediately after the procedure
  • Very low risk of infection compared to implants
  • Less destabilization of the cornea with the SMILE procedure
  • High accuracy of the treatment results even with high corrections, since the femtosecond laser is not influenced by environmental conditions compared to the excimer laser
  • fewer problems with dry eyes after surgery
  • More than 30,000 successfully performed operations worldwide (as of August 2013)

Disadvantage:

  • The structure of the cornea is destabilized (applies to all changes in the corneal curvature using a laser), but to a lesser extent with the SMILE procedure than with other methods
  • The flap entails various risks (only applies to FLEX - see risks)
  • Maximum possible correction depending on corneal thickness and pupil size (applies to all changes in the corneal curvature by means of laser)
  • the treatment of farsightedness is still in the trial phase

The SMILE procedure leaves the upper corneal layer (especially the Bowman membrane ) almost intact and therefore weakens the mechanical stability of the cornea to a far lesser extent than a procedure with a flap. In addition, significantly fewer nerve fibers in the cornea are severed, so that a lower postoperative risk of dry eyes can be expected.

The treatment results published so far show that femtosecond lenticular extraction is a precise and safe method for correcting refractive visual defects. At this point in time (08/2013) it is available for the correction of nearsightedness (myopia) and myopic astigmatism and, due to the advantages mentioned, is especially suitable for higher corrections.

Risks

As with any surgical procedure, femtosecond lenticular extraction comes with a number of risks. The type and frequency of occurrence essentially depend on the surgeon's experience, the level of correction, the technique used and individual influencing factors.

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 in the eye are also possible.

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 LASIK treatments by a surgeon with that of the following 4800 treatments. The rate for the first 200 LASIK treatments is 4.5%, and only 0.87% for the subsequent treatments.

A 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.

In the first few days after treatment, the cornea may feel uncomfortable. Very often, in 15–20% of cases, dry eyes occur in the first few weeks or months after treatment. The cause of dry eyes is the severing of corneal nerves through the side flap incision. The severed nerves can no longer recognize the desiccation of the corneal surface and tear production and blinking frequency are reduced. Since the SMILE method only makes a small incision on the side, the risk of dry eyes is significantly reduced. If the patient still feels dry eyes, experience shows that this is significantly less pronounced after a SMILE treatment than with other surgical methods.

Another risk is the ingrowth of epithelial cells under the flap. These lead to cloudiness in the affected area, but are relatively easy to remove by the doctor. Due to the small access (2-4 millimeters) in the SMILE treatment, which is up to 80% smaller than in operations with the creation of a flap, the risk of epithelial cell ingrowth is significantly reduced. After the treatment, the flap can be displaced or even separated due to strong external influences. Such a risk exists especially in sports or car accidents. Since the SMILE process works without a flap, this risk does not exist here. This represents a great safety advantage. Finally, with femtosecond lenticle extraction, as with all other changes in the corneal curvature by means of laser, there is a risk of ectasia, but this is considerably lower with the SMILE procedure.

Overall, the incidence of flap-related complications is significantly lower than with LASIK, since all cuts are made by the laser. The predictability of the results, especially with larger corrections, is also better.

literature

Web links

Individual evidence

  1. ↑ 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 . April 2007, ZDB -ID 2522724-5 , p. 72-73 ( bmctoday.net ). bmctoday.net ( Memento from May 19, 2009 in the Internet Archive )
  2. ↑ Refractive Lenticle Extraction (ReLEx). (No longer available online.) Universitätsklinikum Gießen und Marburg GmbH, July 10, 2010, archived from the original on October 18, 2010 ; Retrieved November 3, 2010 .
  3. ↑ necessary examinations before the ametropia can be corrected. ( Memento from January 6, 2013 in the web archive archive.today ) University Hospital Carl Gustav Carus Dresden at the Technical University of Dresden.
  4. ↑ M. Blum, W. SECONDO: Femtosecond Lenticle Extraction (FLEx) . In: The ophthalmologist . tape 107 , no. 10 , 2010, ISSN  0941-293X , p. 967-970 , doi : 10.1007 / s00347-010-2222-8 .
  5. ↑ Walter Secondo, Author Vitae, Kathleen Kunert, Christoph Russmann, Annika Gille, Wilfried Bissmann, Gregor Stobrawa, Markus Sticker, Mark Bischoff, Marcus Blum: First efficacy and safety study of femtosecond lenticule extraction for the correction of myopia: six-month results . In: Journal of Cataract and Refractive Surgery . Volume 34, No. 9, September 2008, ISSN  0886-3350 , pp. 1513-1520, doi: 10.1016 / j.jcrs.2008.05.033 .
  6. ^ Walter Secondo, Kathleen S. Kunert, Marcus Blum: Small incision corneal refractive surgery using the small incision lenticule extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6 month prospective study . In: British Journal of Ophthalmology . tape 95 , no. 3 , March 2011, ISSN  0007-1161 , p. 335–339 , doi : 10.1136 / bjo.2009.174284 .
  7. ↑ Lance J. Kugler, Ming X. Wang: Intrastromal Laser Refractive Surgery. Femtosecond lasers are being used to treat myopia, hyperopia, and presbyopia without trauma to the corneal surface. In: Cataract & Refractive Surgery Today Europe. March 2010, pp. 68-70, bmctoday.net .
  8. ↑ Simulator for twilight and night vision according to LASIK depending on the number of diopters and pupil diameter.
  9. ^ Mihai Pop, Yves Payette: Risk Factors for Night Vision Complaints after LASIK for Myopia. In: Ophthalmology. Volume 111, No. 1, January 2004, ISSN  0161-6420 , pp. 3-10, doi: 10.1016 / j.ophtha.2003.09.022 .
  10. ↑ Individual risk factors for halos, loss of contrast, glare, starburst after LASIK. operationauge.de
  11. ↑ JS Vidaurri-Leal: Complications in 5000 LASIK procedures . In: Group RSSI, ed. Refractive Surgery . 1998, p. 61-64 .