Understanding and safely using ophthalmic lasers

of a range of eye problems with little risk of infection. Many laser procedures are relatively pain free and can be performed on an outpatient basis. The combination of safety, accuracy, and relative low cost make lasers very useful ophthalmic tools. The word laser is an acronym for ‘light amplifi cation by stimulated emission of radiation’. Laser light is coherent (the waves are in phase in space and time), monochromatic (just one colour or wavelength), and collimated (light is emitted as a narrow beam in a specifi c direction). Laser beams are produced by the excitation of atoms to a higher than usual energy state. Laser light (radiation) is emitted as the atoms return to their original energy levels. The main components of a laser system are the laser console, the foot pedal, and the laser delivery system. Different delivery systems, connected to the console by a fibre optic cable, can be used to transmit the laser energy to the patient’s eye (Figure 1): an endoprobe (a small fi bre optic probe that is inserted into the eye), a slit lamp, an operating microscope, or an indirect ophthalmoscope. Different types of lasers emit specifi c wavelengths of light and are used to treat specifi c eye problems. Lasers are commonly named according to the active material used. For instance, an argon laser contains argon gas as its active material, whereas the YAG laser contains a solid material made up of yttrium, aluminium, and garnet. The effects that lasers have on eye tissues are both a function of the molecular composition of the tissue and of the wavelength and power of the laser light. Lasers essentially destroy tissue in order to have a benefi cial effect on the eye. The argon laser emits blue-green wavelengths, which are absorbed by the cells under the retina and by the red haemoglobin in blood. These blue-green wavelengths can pass through the fl uid inside the eye without causing damage. For this reason, the argon laser is used extensively in the treatment of diabetic retinopathy. The argon laser can burn and seal the leaking blood vessels, also known as photocoagulation. Retinal detachment is another serious eye problem that can be treated using an argon laser. The laser is used to weld the detached retina to the underlying choroid layer of the eye. Some forms of glaucoma may also be treated with argon lasers. For instance, angle-closure glaucoma can be treated by using an argon laser to create a tiny hole in the iris (a capsulotomy), which allows excess fl uid inside the eye to drain to reduce pressure. Macular degeneration is sometimes treated with an argon or krypton laser. In this treatment, the laser is used to destroy abnormal blood vessels so that haemorrhage or scarring will not damage central vision. The YAG 1064 nm infrared laser generates short-pulsed, high-energy light beams to cut, perforate, or fragment tissue. For patients that develop posterior capsular opacifi cation after receiving cataract surgery, the YAG laser is commonly used to vaporise a portion of the capsule, allowing light to fully reach the retina. A frequency-doubled YAG green laser (wavelength 532 nm) can also be used to create a capsulotomy to treat angle-closure glaucoma, producing similar results to that of an argon laser. The d iode laser has similar applications to both the argon and the YAG laser. The advantage of diode lasers is that they are much smaller and portable, produce less heat, and require much less maintenance than other types of lasers. Lasers units also include a red pointer or target laser beam, which causes no harm to the tissue, to enable the surgeon to see where the treatment laser shots will land.