ABSTRACT
In this chapter, we provide an overview of the fundamentals of the interaction of light with tissue and how this interaction is utilized in photomedicine.
The interaction of light with biological matter plays an important role in our life; photosynthesis and vision are good examples. Therefore, studies on the use of this interaction to address an issue of utmost importance to mankind, the quality of its health care, have always been an important scientific pursuit. Use of sunlight for therapy has been explored since time immemorial by the ancient civilizations. For example, in India, the therapeutic potential of sunlight was well appreciated, and, for good health, exposure to light from the rising sun and consumption of water kept in sunlight were recommended. Indian medical literature dating back to 1400 B.C. documents the combined use of Psoralea corylifolia L. and sunlight for the treatment of nonpigmented skin lesions (vitiligo) (Pathak and Fitzpatrick 1992). In his book A History of Medicine: Medieval Medicine, Plinio Prioreschi (2003) notes the medieval practices of the use of red light for treatment of smallpox. A resurgence of the use of light in therapy happened in the second half of the 19th century when
the role of sunlight for the treatment of rickets, tuberculosis, etc. was explored and the ability of the invisible ultraviolet (UV) radiation to kill microorganisms was scientifically established (McDonagh 2001). Perhaps the biggest thrust toward phototherapy was a result of the efforts of Niels Finsen, a Danish physician, who carried out several interesting experiments on the therapeutic effects of light and established the role of UV light in curing skin tuberculosis (lupus vulgaris) (Bie 1899) for which he was awarded the Nobel Prize in physiology or medicine in 1903. The use of light for the treatment of tuberculosis remained popular until 1946 when a more effective treatment and cure became possible with the development of the antibiotic streptomycin. Another important discovery made in the early 20th century was by Oscar Rabb, a student working in the laboratory of von Tappeiner in Munich, who found that a low concentration of acridine, which had no effect in the dark, led to rapid killing of the protozoan paramecium on illumination (Moan and Peng 2003). This discovery of photodynamic action also spurred a great deal of interest in investigating the effect of light on living systems and has led to the development of photodynamic therapy (PDT). Presently, PDT is an accepted modality for the treatment of several forms of cancer and some other diseases (Moan and Peng 2003). Other notable uses of light in medicine developed in the 20th century include treatment of neonatal jaundice using UV light (Cremer, Perryman, and Richards 1958), use of the UV-A spectrum of light to suppress the immune system and reduce inflammatory responses in psoriasis (Parrish 1977), and treatment of seasonal affective disorders (Lam et al. 2006).
