Explanation of Terms

General terms are sometimes either misunderstood or not understood at all by some people. We have tried to clear some of these misunderstandings by explaining the following terms:

• Surgery always means damage to the tissue. It doesn't matter whether this is done by a knife or a laser. The amount of damage can vary immensely. Often the tissue reacts by forming scar tissue. Sometimes certain parts react different than others, such as the cornea. The outside membrane (Bowman) always reacts to damage by producing scar tissue. The corneal tissue, on the other hand, barely reacts at all. Preferably, one would change the tissue without leaving any scars. There are two types of surgery, invasive and non-invasive, meaning that it does, of doesn't penetrate the membrane. Effectively, all surgeries are "invasive."

• "Medical emergency versus elective." Refractive surgery is not considered to be a medical emergency. In the future we can surely expect that at least surgeries on for example young children to minimise the chance of amblyopia (lazy eye) will be medically accepted. Right now these type of treatments, along with refractive treatments, are considered elective because they are not emergencies.

• Loss of eyesight and blindness. In medical terms, blindness means not being able to anything, just a black hole. This is, however, not what most people understand by the term blindness. They think they are "blind" because their vision isn't perfect. It is a fact worldwide that vision of 50% with or without correction is considered to be good vision. This type would fall under the loss of vision, not blindness. Eyesight of less than 10% is considered "social blindness ". One is unable to perform daily activities under these circumstances. Eye surgeons prefer to see vision as 100%, although many people tend to be satisfied with just 50%.

• "Safe" and "Effective". A "safe" procedure refers to the chance (zero or little) of short and long term damage. Refractive surgery has its risked attached, just as any other type of surgery. The point is how much risk is acceptable, which often makes the decision making process very difficult. Several different studies can be explained in a number of ways, for example, 7% of all people lasered with the Summitlaser will experience 10-30% vision-loss…is this considered a safe procedure? According to the US government, it is. Another example is how long does one need to research a treatment before performing it on patients and when is it considered safe? There is no doubt that some patients will experience a loss in vision, especially at night, compared to their contact lens period. Very rarely one unlucky patient can experience terrible vision loss or even blindness. The chances are so little, but who decides then whether it is safe or not? On the other hand, the majority of patients will have improved vision, 80-96% of all patients only require very little correction after treatment. The majority of all patients are very happy with the results after 12 months.

• "Optical zones." Every discussion regarding refractive surgery requires an understanding of optical zones. The central optical zone is the area where the light enters with the most "optical information." It's about 4mm. The middle zone is situated between the central and outside zone. The last runs from 7mm to the edge of the cornea. It is important to understand the optical zones, especially in relation to the size of one's pupil.

Light beams are able to enter the eye because the cornea doesn't always have an even curvature. The centre is curved most. Towards the outside of the cornea the curvature gets considerably less, sometimes even irregular. Light beams are curved more precisely in the area of most curvature, in other words; the central zone. Light beams that go past the outside of the cornea can disrupt the sharp image that has been projected by the light beams entering the central zone. 

As the curvature differs between the different zones, the vision ability will worsen and disrupted images will increase. This is usually found in cases where the cornea has been treated leading to an artificial change of shape in the middle zone. One will notice this most in situations of little or no light. A decrease in contrast sensitivity, night vision problems, double vision and star lights are the most common light effects. 

The pupil works as the diaphragm of a camera. Only central light beams can enter through a narrow pupil. Disrupting light beams don't get through. During the day, when the pupil is narrow, one will benefit from the straightness of the cornea. However, once the pupil becomes wider the vision ability will decrease. 

This situation usually only occurs in techniques that abruptly change the periferal zone from central to middle. For example, in techniques such as PRK and RK with the old-fashioned laserbeam. However, modern techniques, where an optical zone smaller than the pupil is accepted (highly shortsighted) can have these side effects as well. This is why it is not advised to treat patients with an optical zone smaller than 5.5mm. Modern lasers have software that allow an optical zone of 7mm or more.