Medical Applications of Lasers
The highly collimated beam of a lasercan be further focused to a microscopic dot of extremely high energy density. This makes it usefulas a cutting and cauterizing instrument. Lasers are used for photocoagulation ofthe retina to halt retinal hemorrhaging and for the tacking of retinal tears. Higher power lasers are used after cataract surgery if the supportive membrane surrounding the implanted lens becomes milky. Photodisruption of the membrane often can cause it to draw back like a shade, almost instantly restoring vision. A focused laser can act as an extremely sharp scalpel for delicate surgery, cauterizing as it cuts. ("Cauterizing" refers to long-standing medical practices of using a hot instrument or a high frequency electrical probe to singe the tissue around an incision, sealing off tiny blood vessels to stop bleeding.) The cauterizing action is particularly important for surgical procedures in blood-rich tissue such as the liver. Lasers have been used to make incisions half a micron wide, compared to about 80 microns for the diameter of a human hair.
Medicine has two prime objectives; first to detect disease at an early stage before it becomes difficult to manage and second, to treat itwith high selectivity and precision without any adverse effect on uninvolved tissues. Lasers are playing a very important role in the pursuit of both these objectives. Due to their remarkable properties, lasers have made possible ultraprecise, minimally invasive surgery with reduced patient trauma and hospitalization time. The use of lasers in surgery is, by now, well established and spans
virtually the entire range of disciplines: ophthalmology, gynaecology, ENT, cardiovascular diseases, urology, oncology, etc. The use of lasers for biomedical imaging and diagnostics and for phototherapy using photoactivated drugs is receiving considerable current attention and is expected to have profound influence on the quality of health care.
Laser spectroscopic techniques havethe promise to provide sensitive, insitu, near real time diagnosis with biochemical information on the disease. These deve-lopments have the potential to change the way medical diagnosis is presently perceived. Instead of a means of solving an already known clinical problem, the diagnosis may in future screen people for problems that may potentially exist. Further, any potential risk factor so detected can be corrected with high selectivity by the use of drugs that are activated by light. Because these drugs are inert, until photoexcited by radiation with the right wavelength, the clinician can target the tissue selectively by exercising the control on light exposure (only the tissue exposed to both drug and light will be affec-ted). A good example is the fast-developing photodynamic therapy of cancer. There are indications that selective photoexcitation of native chromophores in the tissue may also lead to therapeutic effects.