The development of non-invasive, non-toxic, and non-pollutant methods for the treatment of diff erent illnesses represents a constant concern of scientists from the medical fi eld worldwide. In this category fi t the methods based on the use of laser systems, which are successfully applied both in human and veterinary medicine due to the special properties of laser radiation: monocromaticity, coherence, intensity, and directionality. Th e aim of this paper is to present the laser systems used in several domains of veterinary medicine and some experimental results obtained by diff erent authors.
Photodynamic therapy is a local treatment modality for cancer, based on the administration of a photosensitive substance selectively retained in the tumor and aft er irradiation with optical radiation results in the destruction of the tumor tissue in the presence of molecular oxygen. Interaction of these 3 essential constituents: the photosensitive substance, the light radiation (with the wavelength corresponding to maximum absorption of the photosensitive substance), and oxygen, leads to direct eff ects (direct damage to cells) or indirect eff ects (vascular and infl ammation reactions).
To date, in veterinary medicine, only a few studies have been published concerning the application of photodynamic therapy in treatment: esophageal squamous cell carcinoma in a dog (42,43), oral carcinoma cells in dogs (44), prostate cancer, skin cancer (45), osseous tumors (46), and brain tumors (47), and only a few photosensitizers have been tested: 5-aminolevulinic acid, meso-tetra(m-hydroxyphenyl) chlorine, benzoporphyrin derivatives, Al-phthalocyanine, benzophenothiazine, and Photofrin II.
Th ese studies show that photodynamic therapy presents some advantages compared to radiotherapy regarding the number of treatments necessary to achieve the same therapeutic eff ectiveness. From here we can hope that photodynamic therapy can be developed as an alternative therapy in veterinary medicine.
Laser phototherapy is based on laser radiation absorption by cytochromes and porphyrins, from mitochondria and cell membranes, which pass from the singlet ground state 0S in the fi rst excited singlet state 1S*. From the excited state, absorbing molecules can be returned to the ground state by radiative or non-radiative transitions or energy interchange can take place and thus pass to the triplet excited state 3T1*. Molecules in the triplet excited state transfer their excitation energy to the molecular oxygen (which is in the triplet state in its ground state), which passes to its lowest state, the excited singlet.
Singlet oxygen is part of free radicals and is one of the most active forms in cellular metabolism. Production of singlet oxygen leads to the formation of proton gradients across cell membranes and mitochondrial membrane. Th ese gradients of protons change the permeability of cell membranes to diff erent ions and mitochondrial membrane permeability, which leads to metabolic changes in the cell. These metabolic changes induced by low power laser radiation at the cellular and subcellular level lead to the development of procedures for the treatment of soft and hard tissue diseases.
The clinical applications of lasers, initially confi ned to surgery, have been extended in recent years to almost all areas of veterinary medicine. This wide use of lasers in veterinary medicine opens new perspectives in the treatment of soft and hard tissue diseases as an alternative, non-invasive, non-toxic, and low cost method for the benefi t of patients.