The first excimer laser was invented and displayed in 1971 by N. Basov, V. A. Danilychev and Y. M. Popov at the Physical Institute named after P.N. Lebedev (Moscow). The laser used bixenon (Xe2) excited by an electron beam to give stimulated emission at 172 nm wavelength. Later mixtures of noble gases with halogens were tested, which were patented in 1975 by George Hart and Stuart Searles from the research laboratory of the U.S. Navy. Excimer laser was first used by the IBM corporation for computer chip etching.
In 1981, Dr. Rangaswamy Srinivasan discovered that ultraviolet excimer laser is able to cut a living tissue precisely without causing any thermal damage to surrounding area. The principle of ultraviolet radiation on organic compounds deals with breaking intermolecular bonds and, thus, changing the state of a tissue from solid state into gas (photoablation – evaporation).
In 1981, ophthalmologists started to cooperate with scientists with the aim to improve the procedure to apply it to the eye cornea.
In 1985, in Berlin, the first laser correction, a PRK with the use of excimer laser, was performed.
All excimer lasers operate at the same wavelength range, in pulse mode (usually with the frequency of 100 Hz and impulse length of about 10 ns, but sometimes the values may be as high as 200 Hz and 30 ns) and differ only in the laser beam form (a scanning slit or a ‘flying spot’) and the composition of active medium (inert gas).
A laser beam, resembling a slit or a spot in the cross-section, moves along a certain path gradually removing (evaporating) corneal layer and reshaping it. The temperature at the ablation area remains practically unchanged (not more than 5°-6°) due to a short-term impact. Another essential feature is precision. Each impulse of the laser is accompanied with removal of a layer of 0.25 µm in thickness (about 1/500 the thickness of a human hair). Such precision allows to obtain perfect results after laser vision correction.
Depending on the laser vision correction method the following equipment is used:
Allegretto Wave Eye-Q Laser System has the pulse frequency of 400 Hz which makes it fastest in the world reducing time necessary to perform am Excimer-laser vision correction. Shorter corneal exposure means faster rehabilitation and excellent post-surgery outcomes. Allegretto Wave Eye-Q laser ray has super-thin smooth shape creating ideal cornea surface and bring up recovery period to a minimum. The optical system of Allergretto Wave Eye-Q laser is fully sealed therefor it cannot be affected by outside factors like humidity or temperature in the room.
Limitations for the used of Allegretto Wave Eye-Q:
myopia from -0.5 D to 14.0D;
hyperopia from +0.5 D to +6.0 D;
astigmatism from ±0,5 D to ± 6.0 D.
The Allegretto Wave Eye-Q system uses the following state-of-the art technologies:
- Perfect Pulse Technology spares eye tissue ata maximum.
- Wavefront Optimized Technology preserves the natural cornea shape escaping unnecessary applanation and thus preventing spherical distortions.
- Topography-guided ablation. Wavefront-Guided personalized ablation procedure fixes all the distortions of the optical system.
- The 3-D Eye-Tracker system registers the eye position and movements.
- NeuroTrack system controls eye rotation movements.
Alegretto Excimer-lasers are the only ones at present to be linked to optical topography devices: Toplyzer corneal topographer, Oculyzer diagnostic station, Analyzer aberrometer. The system is unique as it can be connected with a femtosecond laser allowing to perform IntraLasik laser corrections.
VISX Star S vision correction systems deliver a package of seven beams in the scanning spot shape, ensuring ideal smoothness of corneal cut. The seven beams package covers at once vast corneal area thus providing quick and effective tissue evaporation. The offset scanning module incorporated into this laser model allows simultaneous correction of hypermetropy mixed astigmatism and irregular astigmatism caused by previous unsuccessful refractive operations. This laser is also equipped with the eye tracking system which monitors minor shifts of pupil centre during the correction and adjusts the laser beam targeting to the specified area throughout the correction procedure.
VISX Star S vision correction range:
Nearsightedness (miopia) - up to -15.0 D
Farsightedness (hyperopia) -up to +4.0 D
Astigmatism - up to +/- 3.0 D
VISX Star S4 IR Excimer Laser is quite different from other models as it allows to deliver Excimer-laser correction to patients with complex forms of myopia, hyperopia and higher order aberrations.
The new complex approach incorporated into VISX Star S4 IR ensures maximum smooth cornea surface during the laser correction, while monitoring all possible movements of the patient's eye in the course of the surgery, all together allowing maximum compensation of most complex aberrations in all eye optic structures. These advantages greatly lower probabilities of post-operative complications, seriously reduce rehabilitation period and guarantee best outcomes.
VISX Star S4 IR vision correction range:
Nearsightedness (miopia) - up to -16.0 D
Farsightedness (hyperopia) -up to +6.0 D
Complex astigmatism - up to +/- 6.0 D
NIDEK EC-5000 Excimer-laser beam has a scanning slit shape. NIDEK EC-5000 is equipped with the gas survivability system, ensuring stable emission characteristics. This laser is very accurate, simple for operation, absolutely safe for eye cornea. It is designed for laser corrections using PRK and LASIK techniques. In the course of the operation NIDEK EC-5000 using the scanning slit mode affects the whole cornea. The scanning slit beam provides for true spheric cornea shape, while adkusting it's optic power.
Vision correction range:
Nearsightedness (miopia) - up to -15.0 D
Farsightedness (hyperopia) -up to +6.0 D
Astigmatism - up to +/- 6.0 D
WaveLight FS200 Femtosecond Laser has the highest speed of corneal flap modeling. E.g. other laser models shape flaps in 20 seconds while the femtosecond laser FS200 WaveLight can manage the procedure in 6 seconds! FS200 WaveLight Femtosecond Laser shapes the corneal flap during an Excimer-laser correction by very fast laser beam pulses.
The Femtosecond laser uses infra-red light rays for precise tissue separation at a prescribed depth, the process is called “photo-rupture”. Laser energy pulse is focused at the exact location inside the cornea, thousands of laser pulses are located next to it to create a section plane. Using laser pulses in the prescribed algorithm and at the prescribed depth in the cornea, it is possible to create a corneal flap of any shape and at any depth. This means that the unique features of the Femtosecond Laser allows the ophthalmic surgeon to create a corneal flap fully controlling it’s diameter, thickness, alignment and morphology, with minimal architecture disturbance.
Femtosecond lasers are most commonly used in Femto-Lasik Excimer laser correction procedures, which are different from other methods, as corneal flaps here are created by laser rays, rather than mechanical keratomes. Absence of mechanical impact increases laser correction reliability and by large decreases the risk of the acquired post-operative corneal astigmatism, also it can be used in patients with thin cornea.
Since the FS200 WaveLight femtosecond laser is a part of the Allegretto Excimer laser system the total time of Excimer-laser correction procedure is minimal.
Capabilities of the femtosecond laser, e.g. in most accurate corneal flap modeling are also used for a corneal tunnel creation for intra-stromal rings implantation.
IntraLase FS60 Femtosecond Laser has high frequency and short pulse duration. The pulse duration is measured by femtoseconds in this case (picoseconds, 10-15s), this enables to separate corneal layers at molecular layers without heat emission and mechanical impact on the surrounding tissues of the eye. The flap creation procedure is non-contact (no mechanical cuts in the cornea) and takes only few seconds.
The IntraLase FS60 Femtosecond Laser is integrated into iLasik equipment system. It operates in link with VISX Star S4 IR Excimer Laser and WaveScan Aberrometer. The system allows to perform vision Laser correction considering the tiniest individual features of the patient.
The result of a laser correction depends on many aspects, including a specialist’s experience, the applied treatment method and a the laser used. The microkeratome is no less significant for treatment though. This unit is used for excimer laser correction in compliance with the LASIK method. Microkeratomes are very safe. They operate irrespective of power supply. In the course of LASIK treatment, it is the internal corneal layers that are being exposed, and not the external ones. A microkeratome is used to separate the very surface layers.
The Excimer Eye Clinic uses microkeratomes of the world-known brand ‘Moria’ in its practice. It was one of the first brands that started manufacturing automatic models instead of the manual ones. They minimize risks of excimer laser corrections and enhance its quality.
Moria Evolution 3
This type of microkeratome enables to perform preparation for excimer laser vision correction (that is the flap formation) in the way that would be less painful for the patient and minimizes discomfort. The instrument is equipped with multiuse heads (90 µm or 130 µm), fixation vacuum rings from -1 to +2, and rotational automated microkeratomes. The structure of mikrokeratotome rings and heads allows flexible adjustment of equipment to individual eye peculiarities for more precise and secure results. Microkeratomes (Moria Evolution 3; Moria Evolution 2; Evolution II LSK, Moria) used in Excimer Clinics allow flexible tuning of the equipment to the individual features of the patient's eyes ensuring more accurate and reliable outcomes.
Epi-K epikeratome is used for Epi-Lasik excimer laser corrections. Unlike other microkeratomes, Epi-K epikeratome is equipped with a disposable plastic head with an applanation plate for forcing through (applanation) of epithelium.
Epi-K epikeratome is used to separate the corneal epithelium from Bowman`s membrane leaving a clear optic area for laser ablation. Epi-LASIK maintains the corneal structural integrity better, gives a shorter period of visual functions recovery, reduces the risk of corneal hazes (keratoleukoma) in comparison with PRK and LASEK.
The unique epikeratome structure allows formation of smaller epithelial flap with minimum tissue resistance. An epikeratome slides over the surface of the cornea, incising the epithelial layer with the stratum but without cutting the Bowman`s membrane. In the course of Epi-K procedure, no stromal damage has been found.