How does the excimer laser works?

Briefly, laser stands for “light amplification by stimulated emission of radiation”. Laser light is created when energy is applied to a mixture of gases. Two gaseous elements such as argon and fluoride in a helium premix are jolted to a higher energy state with thousands of volts of electricity. These elements combine to form an unstable compound. As the excited ionized atoms dance within a mirrored tube that reflects the light back at them, they release an intense concentration of light energy. Eventually, the light beam becomes so energized that part of it escapes from the tube through a hole in the semi-silvered mirror. Such laser light – unlike sunlight – is focused in one direction at one wavelength. In other words, the light rays vibrate together in phase to form a “coherent” monochromatic laser beam.

The essential point for patients to understand about the excimer laser system is that their doctor needs to grasp fully all the intricacies of how the instrument works. A surgeon must know how the characteristics of the laser beam are affected by its environment – by temperature and humidity – and how the device is tested or calibrated before each surgery. Even the altitude of the clinic affects results and is factored into the mathematical formulas that control the excimer. Lasers are not static instruments. They are constantly changing. Replacing a lens in the optical system or replenishing the laser's gases affects the characteristics of the beam.

Ophthalmologists would never perform laser eye surgery without knowing the machine and also the laser must be recalibrated before each patient.

Rather as a fine violin should be tuned before every symphony, an excimer laser must be carefully tested before each procedure. The violin's pitch can shift ever so slightly with each stroke of the bow. The profile of the laser beam varies minutely with every pulse. Like the violinist, the surgeon must know that the laser is “in tune” so that it can perform well.

Some patients worry that any one laser pulse might negatively affect the final outcome. With a great painting, no single, tiny brush stroke brings the final picture to life. With refractive excimer laser surgery, no one laser pulse has a noticeable effect on your ultimate vision. In fact, the slight, natural micro-movements of the eye add to a blending or polishing effect. Rather as the accumulation of many delicate brush strokes creates a Rembrandt's poignant emotional impact, the sum of a pre-set number of laser pulses produces the joy of finely sculpted vision.