How Can a Laser Correct Your Vision?

Not all lasers could correct your vision. Some could destroy it. There are a great many different types of laser, all man-made for different purposes. The one used for vision correction is called the Excimer laser – a name which means little to anyone except the people who first developed this type of laser. They made the word up, from two other words: excited and dimer. The story as to why is not relevant to the exciting world of LASIK.

Eye surgery, like every type of surgery, has been transformed by lasers. The excimer laser which does Custom LASIK, PRK, IntraLase, LASEK, and epi-LASIK procedures comes as part of a system of sophisticated technology and is a major investment for the eye surgeon.

How is a Laser Different From Other Lights?

Laser lights:

· Travel in rays that are parallel to each other;

· Are directional; and

· Have a single vibration.

Lasers are focused lights, rather than scattered like headlights or flashlights. That is why they make good classroom pointers. It’s also why they are excellent for eye surgery, because they can be made to come to a microscopically tiny focus.

Lasers and Heat

All lights generate heat and all hot things give off light. Light and heat are two aspects of the same energy. Some lasers are so hot they can slice through a block of steel. Some lasers used in dentistry and medicine are referred to as “cool” lasers, and the excimer laser is one of those. Cool lasers are both inherently cooler than some other types of laser, and also deliberately cooled for medical use.

Lasers and Color

Since all lasers have just one vibration level, they are a single color. Some have visible colors and some are infrared or ultraviolet – their vibration is beyond our visible color spectrum. Excimer lasers are ultraviolet.

How the Excimer Laser Works

The total vision correction system containing the excimer laser includes a patient bed, a computer and monitor, a tracking device to keep the laser targeted on each eye’s treatment area, a microscope for the eye surgeon to see your eyes highly magnified, a seat for the surgeon, and some tools and implements.

By the time you are on the patient bed for your vision correction, your two eyes have been precisely diagnosed as to their refractive errors. That is the first part of a Custom LASIK surgery, done before the day of your treatment. Your treatment plan is based on two 3-D maps generated by the diagnostic Wavefront equipment. They are microscopically exact maps of each eye’s contours and shape.

The excimer laser is programmed to follow these two maps during treatment, subject to your eye’s surgeon’s control. First a thin flap of surface tissue is folded back on the cornea (front transparent part of the eye), to expose the next layer down, the stroma. Then the excimer laser is directed on the pre-determined treatment area, and quickly vaporizes tiny pieces of unwanted tissue, at pre-set depths.

A New Corneal Contour

Your eye doctor planned the tissue vaporization so as to reshape the cornea. The cornea bends (refracts) light entering the eye, and in a 20/20 eye focuses it on the retina (“camera film”) at the back of the eye. Modifying its curvature changes the cornea’s degree of light refraction.

· If you are nearsighted (myopic), your eye surgeon will use the excimer laser to remove pieces in the center of the cornea. That slightly flattens the corneal curvature, and now light will not be refracted quite so much. You will have clear distance vision.

· If you are farsighted (hyperopic), your eye doctor will remove tissue from the periphery of the cornea, to slightly steepen its curvature. Now light will be refracted a bit more and you’ll have clear close-up vision.

· If you are astigmatic, your eye surgeon will remove tissue in an individual way according to your eye’s particular oval shape, to create a more round shape. An astigmatic eye is like a football, with a lengthwise flatter curvature and a crosswise steeper curvature. After it is made round, light will be refracted in only one way instead of two.

Lower and Higher Order Aberrations

No treatment plan is as simple as the above makes it sound. Many people are both astigmatic and myopic, for instance; and we all have tiny imperfections called Higher Order Aberrations. They are subtle defects like halos around light sources, poor night vision, and ghosting – faint duplicate images.

Myopia, hyperopia and astigmatism are the three Lower Order Aberrations. Custom LASIK corrects both higher and lower order aberrations. That allows you to (a) see more, because you have clarity at all distances; and (b) see better, because none of those subtle defects get in the way.

If you are considering a LASIK procedure, the best thing you can do to obtain excellent results is to choose a well-qualified eye surgeon. The best LASIK surgeons screen their patients very rigorously because it is in nobody’s best interest to perform a procedure on somebody who is a poor candidate for it. So do some homework before you choose your LASIK surgeon, and choose one who has many years of experience and has done several thousand procedures of the type you need.