The History of Ophthalmology
Part 6: What is a Laser?
Lasers are central to current refractive surgery, but they were not at first used for ophthalmology. The first laser was developed at Bell Labs in 1958. The two researchers were working on microwaves and wanted a way to see molecules more clearly. They had no idea their new light would form a multi-billion-dollar industry and revolutionize many industries as well.
All lasers are lights man-made for specific purposes. The term laser started as an acronym for Light Amplification by the Stimulated Emission of Radiation. The first working laser was demonstrated in 1960 at the Hughes Research Laboratory in Malibu. It used a ruby crystal and generated a red light at 694 nanometers wavelength.
Lasers are classified according to the medium used to generate them: solid, gas, semiconductor etc. What makes them powerful and precise is that (a) their light rays travel in a parallel fashion; (b) they are directional and do not scatter like those of a flashlight or incandescent light; and (c) they contain a single wavelength (color).
Light and heat energies travel in waves which have specific wavelengths and frequencies. The range of waves that we can see – the visible spectrum – is a very small part of the entire electromagnetic spectrum. Each laser has a specific wavelength which gives it a specific color and temperature. Lasers can be infrared, ultraviolet, or of a visible color, depending on what wavelength is needed to accomplish their purpose.
The longer the wavelength, the slower the frequency, and vice versa. So for example, AM radio waves are longer and slower than FM radio waves. X rays are shorter and faster than UV rays.
Isn’t Radiation Harmful?
The term radiation has acquired a negative connotation to some extent, as in “UV radiation”, which can cause skin cancer. But basically it’s a neutral term referring to the travel of:
- Visible light
- Radio waves
- Infrared and ultraviolet rays
Damage will only happen when the energy source has a wavelength inappropriate to where it is targeted. Benefits can equally well happen, as when X-rays are targeted on a malignant tumor. Cancer cells multiply more quickly than normal body cells, which makes them more vulnerable to the radiation.
Lasers for Ophthalmology
The laser used for vision correction is the Excimer laser, developed in 1973 at the University of California. It is a pulsed gas laser in the ultraviolet range and has a very rapid frequency. Each pulse removes a microscopic piece of corneal tissue about as thick as 1/500 of a human hair.
The laser used in IntraLase to create the corneal flap (instead of using a microkeratome) is a femtosecond laser – its pulses last between 50 and 1,000 femtoseconds (and a femtosecond is a quadrillionth of a second). That means they are too brief to burn the cornea. They vaporize corneal tissue one molecule at a time, below the surface, without damaging the surface tissue, or any other nearby tissue.
History of Ophthalmology Part 1: The Ancient World
History of Ophthalmology Part 2: The Middle Ages: Spectacles
History of Ophthalmology Part 3: Anesthesia and Infection
History of Ophthalmology Part 4: The Nineteenth Century: Seeing the Eye
History of Ophthalmology Part 5: The Twentieth Century: Swift Progress
History of Ophthalmology Part 7: Leading up to LASIK
History of Ophthalmology Part 8:LASIK Into the Twenty-First Century