How Does an Excimer Laser Work in Laser Eye Surgery?

Excimer lasers emit light, i.e. photons, of a defined wavelength. These photons (light) are invisible to us because their wavelength can't be perceived by our visual system. The same holds true for the ultraviolet radiation of the sun. These "excimer photons" are created during the decay of excited dimers (excimers). The excited dimers consist of two identical or different atoms of an inert gas/halogen mix like ArF*, ArAr*, KrF*, XeF*, etc., and they exist only in this excited state marked by "*". Depending on the composition of the gas excimers are created by electronic excitation. When these excimers decay they emit photons of a defined wavelength, i.e. engergy, for instance NeF* 108nm, ArAr* 126 nm, XeF* 351 nm. Due to their high energy (small wavelength) these photons can break down chemical bonds like C-C or C-H bonds. Biological molecules like those present in the cornea of the eye are mainly composed of C-C and C-H bonds, which are attacked by the photons of the excimer laser in laser eye surgeries like LASIK, LASEK, PRK. This means that the organic components are vaporized and ablated and the refractive power of the cornea changes. As already indicated, excimer lasers emit almost exclusively photons of a certain wavelength in the short-wave ultraviolet range. Infrared radiation (long-wave radiation) like the one used in microwaves to heat up food, is not emitted. This is the reason why the excimer laser is called a cool laser, which means that during the destruction of tissue the surrounding tissue is almost not heated up, thus making the laser a highly precise instrument.

Note: Ultraviolet radiation can damage tissue, for instance in the case of sunburns, and cause alterations in the DNA which can result in the development of cancer. Excimer lasers work with high-energy ultraviolet radiation. So theoretically, there is always the risk of damage after laser eye surgery. So far the literature hasn't provided any information on this matter.

Fig. General chart of excimers, the wavelength of their photons when they return in the unexcited state, chemical bonds und the associated dissociation energy.