LASIK is an eye procedure that permanently alters the cornea’s shape (the clear covering on the front of the eye). It is carried out to enhance vision and lessen the need for eyeglasses or contact lenses. UV lasers for eye surgery are now a standard procedure in ophthalmic surgery.
History
This is one of the important for the Institute of Laser Physics SB RAS and SF IRTC “Eye Microsurgery”, the experience of successful cooperation over 30 years. Researchers from these organisations started working together in the 1980s to investigate the potential applications of high-power, short-pulse UV laser light in medicine.
By the time the team had a complete set of pulsed excimer laser sources, most of which were created at the Institute for the first time in the world. Then in 1986, the world’s first operation of laser correction of refractive errors was made.
The authors of many research papers have proposed and practised separation of the corneal stroma to keep the Bowman’s membrane with an epithelial layer, which would inevitably evaporate when exposed to and to hold direct ablation of the corneal stroma.
Thus, the corneal flap is folded to one side. Results of clinical trials for the correction of high myopia in several patients were reported. S. Trokel, a renowned ophthalmologist and professor at Columbia University in New York, USA, noticed that Russian researchers made a substantial contribution and dubbed the initial procedure “proto-LASIK”.
Eventually, with the development of the mechanical microkeratome for the corneal bundle, this corrective technique was finally developed as LASIK, which is still the most widely used technique for laser refractive error correction.
Description of the process
The cornea and lens of the eye must correctly bend light rays for vision to be precise, making it possible for images to focus on the retina. The pictures will be hazy otherwise.
A “refractive error” is the term used to describe this blurriness. It results from an imbalance between the length of the eye and the cornea’s curvature.
LASIK removes a small layer of corneal tissue using an excimer laser (an ultraviolet laser), altering the cornea’s shape to ensure light rays are sharply focused on the retina. The cornea becomes thinner after LASIK surgery.
Contacts or lasers
For years there has been a growing interest in the refractive surgery of the human eye by the emission of excimer lasers surgical means rather than spectacles or contact lenses. Excimer lasers can emit different wavelengths in the ultraviolet region, including 193, 222, 248, 308, and 351 nm. Since it generates the most exact cuts with the least thermal deformation of the tissue’s surface, 193 nm is the preferred wavelength for corneal surgery. Therefore, the excimer ArF laser, which emits light at a wavelength of 193 nm, is typically used by surgeons. However, different research groups study the possibility of applying other laser wavelengths for refractive surgery.
A MedilexTM UV ophthalmic laser system based on excimer ArF (193 nm) or KrCl (222 nm) lasers is described in one article. It has been demonstrated that using 222 nm rather than the more common 193 nm wavelength for photorefractive surgery provides several health and technical benefits, and we propose that the emission of the wavelength of 222 nm of the KrCl excimer laser is preferable for refractive surgery than traditionally used wavelength of 193 nm.
The Photorefractive Keratectomy (PRK) or Laser in Situ Keratomileusis (LASIK) procedures can be used to correct myopia, hyperopia, astigmatism, and myopic or hyperopic astigmatism, as well as Phototherapeutic Keratectomy (PTK) to treat corneal diseases.
All procedures mentioned above can be realized using either the wavelength of 193 nm of the ArF excimer laser or the wavelength of 222 nm of the KrCl excimer laser.
A laser subsystem, an optical subsystem, an alignment subsystem, a measurement subsystem, and a control subsystem make up the MedilexTM UV ophthalmic laser system.
The laser subsystem produces pulsed coherent UV radiation with the appropriate energy level and wavelength. The optical subsystem provides a method for preparing and delivering the beam to the patient’s eye. The laser beam is aligned to the centre of the patient’s eye by the alignment subsystem, which also offers a microscope. The measurement and control subsystem provides the computer and electronics circuitry required for monitoring and controlling all set-up systems via a microprocessor device.
By observing a decrease in antibody levels to native DNA antigens, it is possible to conclude that laser therapy using 193 nm laser radiation does not damage cornea tissues in an irradiated area. However, the absence of such an effect can indicate inefficiency in treatment as to an effect upon HSV.
The laser with the given wavelength has an inefficient energy for coagulation of HSV on the cornea’s surface and does not cease an inflammation formation. The further formation of inflammation is confirmed by high CIC levels that indicate a continued humoral response to antigen stimulation. Thus, using the 193-nm radiation wavelength is ineffective in treating herpetic keratitis manifested with arborescent surface keratitis.
Conclusion and learning
The basic ab-extern method of laser irradiation is the maximum thinning of trabeculae and Descemet’s membrane while maintaining the integrity of these tissues to achieve the maximum antihypertensive effect by restoring the ocular fluid filtration. Descemet membrane and layered evaporation (ablation) trabeculae are the methods used to increase the filtering properties. The ophthalmologist determines the duration of exposure in each case as the current intensification of aqueous humour. The main advantage of excimer laser surgery is the high precision tissue removal and surface quality without thermal injury.
So thinning was necessary to develop an optical system that allows the delivery form, focuses the UV laser radiation on the biological tissue’s surface, and delivers 308 nm to the surgical field. A flexible fibre light guide with an easy-to-use handle was made. The optical system of the laser system is designed to transport laser radiation, transforming the geometrical dimensions of the laser beam focused to a diameter of about 0.05 cm and, subsequently, the transmission of focused radiation on the surface of Descemet’s membrane.
