Excimer Laser

Everything There Is to Know About Excimer Laser 

An excimer laser is a strong kind of radiation that emits very concentrated light in the ultraviolet region of the spectrum and generates nanosecond pulses. It uses a noble-gas halide. Excimer is a chemical term that refers to a material formed by the combination of two atoms or molecules of similar chemical composition in an agitated state; it is an excited dimer. Its gain medium is a mixture of gases, usually a noble gas such as argon, xenon, or krypton and a halogen such as fluorine or chlorine, apart from helium or neon as a buffer gas. The gain medium gets pumped with short current pulses in an exorbitant-voltage electric discharge otherwise sometimes with an electron beam, that creates so-called excimers – molecules which show a bound state of its constituents only in the agitated electronic state, and not in the ground state. Its uses are in ophthalmology to vaporize some part of the top layer of the cornea and to reshape it, correcting refractive errors from astigmatism, myopia, and hyperopia. It has uses in dermatology as well to treat vitiligo and psoriasis.

History of Excimer Laser

The excimer laser got invented in 1970 by Nikolai Basov, V. A. Danilychev & Yu. M. Popov, in Moscow, at the Lebedev Physical Institute. It involved using a xenon dimer agitated by an electron beam to produce stimulated emission at a wavelength of 172 nm. Its discovery was within a short time frame of 1 year after the exploration of fluorescence spectra of active molecules of the rare gas monohalides. In 1974, several groups like Kansas State University, the Avco Everett Research Laboratory, USA, and the University of Cambridge, UK, did investigations on fluorescence spectra of other rare gases. 25 years after discovering, it has been used progressively in a variety of medical, R&D, and industrial applications. The key to its success is its unbeatable Ultraviolet performance. Evolutionary and revolutionary technological achievements have interpretations into significant enhancements of the performance, the parameters, the reliability, and the ease of handling of these radiations. Today, the installation of almost 7000 Lambda Physik radiations have taken place worldwide. The number of established emissions is rapidly increasing because fields of applications in industry and medicine have widened. For the year 2001, the amount of emission needed worldwide was about 2000–for medical, scientific, and industrial use. 

Indications to use excimer laser

The primary use of an excimer laser is in dermatology and ophthalmology, which helps diagnose several disease processes, including:

  • Gene manipulation  
  • Bioengineering applications 
  • Refractive Surgery in Ophthalmology 

The radiations with wavelengths less than 350 nm are useful in these procedures that use the non-thermal ablation effects. The surgeries reduce myopia, astigmatism, hyperopia, and some high-order vision abnormalities. In the central cornea, the optical zone ablated is usually 5 to 6.5 mm. Removing 6–15 μm of stromal tissue reduces the refractive error by 1 Dpt. The depth of ablation depends on its diameter. The selection of ablation profile & volume is either to remove low-order aberrations only or high- and low-order aberrations.

  • In Trabeculostomy 

In trabeculostomy, the excimer laser got used for the first time in 1998. Now they help treat the pathology, causing open-angle glaucoma. The radiations deliver photoablation energy to remove the tissue that obstructs fluid outflow accurately. It does minimal thermal damage to side-line tissue. The surgeries are in practice as an outpatient procedure, and under topical anesthesia. After paracentesis and stabilization of the anterior chamber by viscoelastic, the surgeon enters a fiber optic probe, advances it across the anterior chamber, and places it along with the trabecular meshwork. Surgeons control the probe placement using direct observation by an endoscope or a goniolens. He forms four to ten openings into Schlemm's canal, removes the probe and the viscoelastic, and monitors the patient postoperatively.

  • In Acute Myocardial Infarction 

An excimer laser is a useful interventional tool best for targeted thrombus removal. Patients who experience chest pain with persistent ischemia have unstable hemodynamic conditions. The patients show a failure to respond to thrombolytic pharmacotherapy or have contraindications to these medications. The radiation can simultaneously treat plaque and accompanying thrombus. Maximal thrombus removal is directly proportional to the thrombus burden. The higher the initial thrombus burden on the target lesion, the higher gain, and more effective dissolution occur.

  • Radiation Atherectomy 

In these procedures, the first thing is to select an appropriate setting and size for the catheter. Catheter selection always depends on the size of the vessel & the nature of the lesion. Usually, the largest diameter catheter gets a preference to accommodate the vessel. However, more diseased lesions, heavily calcified vessels will not yield to large diameter catheters. Thus, severe wounds warrant the selection of decreased diameters catheters. As per Spectranetics guidelines, the diameter of the radiation catheter should not exceed two-thirds of the particular vessel diameter.

  • Photo-Thrombectomy in Lower Limbs Vessels

The procedure uses energy to ablate thrombus. Thrombus absorbs UV, visible and mid-infrared wavelengths, making it the best target for glare ablation. Angiographically, the radiation reduces the severity of lesions from 100% to 66.75%. The radiation symbolizes the thrombus like other atherectomy & thrombectomy devices. The presence of thrombus is a forecaster of distal embolization. 

  • For Tissue Repair and Regeneration 

The use of the excimer laser and its way of applications has revolutionized refractive surgery. It is the best example of how a surgical technique modifies wound healing. The most commonly used method is glare in situ keratomileuses, as it causes less haze, regression, and pain. It shows faster recovery as compared to surface treatments like PRK, epi-LASIK, or radiation subepithelial keratomileusis. LASIK shows the advantage of bypassing epithelial injury and, thus, the epithelial-stromal response of wound healing.

Complications of using Excimer Laser 

During surface ablation, haze is the most common complication. Postoperative Flap Complications:

  • Interface complications are new as the interface between flap & stroma presents a space where fluid can accumulate. 
  • Flap slippage happens during the starting days of surgery and should be treated as soon as possible.
  • Dry eye syndrome is the most common complication after LASIK. It is generally benign and may cause notable visual impairment in some cases.
  • Diffuse lamellar keratitis mainly happens within the first few postoperative days & its treatment should bypass scarring. 
  • In the interface, corneal hydrops with fluid accumulation is a rare but essential phenomenon about steroid-induced glaucoma.
  • Epithelial ingrowth is another rare problem generally requiring treatment. 
  • Corneal ectasia is very rare, and in most cases, it is about thin stromal beds. Anyhow, its pathogenesis is not entirely understood, as it may also occur in healthy eyes. 

Alternative Instruments 

The high-speed UV radiations of solid-state laser make it an alternative to the excimer laser. The substantial state radiation can do refractive surgery at a lower cost than the excimer laser.

Specifications of excimer laser

  • Energy range: 100Hz
  • Pulse length: 15nS
  • Beam size: 8x3-5 mm
  • Divergence: 1x2 mRad
  • Temporal coherence: 0.5mm-2mm

How excimer laser works

It is a powerful kind of laser that nearly always operates in the ultraviolet (UV) spectral region and generates nanosecond pulses. Its gain medium is a gas mixture, generally consisting of:

  • A noble gas also called rare gas, for example, argon, krypton, and xenon.
  • A halogen gas, for example, fluorine or chlorine-like HCl.
  • Helium and neon that acts as a buffer gas. 

An excimer gain medium gets pumped with short current pulses in an electron beam or a high-voltage electric discharge that creates excited dimers molecules that represent a bound state about their constituents in the excited electronic state, and not in the electronic ground state. After spontaneous or stimulated emission, the dimer molecule rapidly dissociates. So, reabsorption of the produced radiation gets avoided. It becomes possible to attain a reasonably high gain from a moderate concentration of excimers. Different types of emissions usually emit at wavelengths of 157 to 351 nm. As excimer lasers utilize molecules as the gain medium, they can also be named molecular lasers.

Market Leaders 

  • Deka

Especially for Psoriasis and Vitiligo Progressive Action to reduce Vitiligo and Psoriasis: No Drugs are necessary for treatment; it is painless and a rapid procedure.

  • Kernel Medical Equipment

This equipment is best for inflammatory skin disease.

  • Philips Volcano

The only PMA approved radiation system & disposable catheters for the treatment of peripheral and coronary arterial disease. These are best for atherectomy treatments.

  • Carl Zeiss Meditec 

They are specially for the requirement of the modern refractive surgeon. They are best for ophthalmic refractive surgery.

  • Alcon

It is the only excimer laser to operate at 500 Hz, with an average treatment time of approximately 1.4 seconds per diopter.

  • NIDEK

They are suitable for ophthalmic refractive surgery. They comprise the OPD-Scan III, EC-5000CXⅢ, and Final Fit

  • SCHWIND eye-tech-solutions

The brand has the best precision, speed, and safety measures for treatment. The excellent 0.54 mm spot further enhances the accuracy & smooth corneal modeling.

  • Johnson & Johnson Vision

The design of the STAR S4 IR™ System is to bring advanced laser vision correction to life. It has a VSS Refractive technology, which makes it's functioning flawless.

  • Ziemer Group

Wavelength: 1,053 nm

It is 10 to 100 times faster than all other radiation systems. It has the smallest spot size, the lowest pulse energy, and the most rapid Femto-LASIK procedure.

  • Spectranetics

Wavelength: 308 nm

Spectranetics manufactures and markets the disposable catheters for the treatment of coronary and peripheral artery diseases and the only excimer laser system and lead extraction & management. 

Conclusion 

The excimer laser is an ultraviolet spectrum-based radiation system that uses a noble gas haloid for its functioning. Along with noble gas, the system has a halogen, such as chlorine or fluorine. It is best in ophthalmology and dermatology treatments. Also, it has uses in refractory and atherectomy surgeries. On interfaces, the laser has some complications too. Overall, it is the best addition to the medical field as it also helps in bioengineering applications, gene manipulations, thrombus removal, and other diseases of coronary arteries like plaque ablation.

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