Refractive Corneal Surgery: A Medical Advance of our Time

by Renato Alberto Meduri

Advanced techniques to reshape the curve of the cornea eliminating myopia, astigmatism and hypermetropia.

In the '70s, Fiodorov, a Soviet ophtalmologist, structurally modified the curvature of the cornea to correct myopia, a medical advance of our time.
To intuition, Americans have added technology by substituting man's most stable hand and introducing constant and dependable laser radiation. Modern refractive surgery allows the reshaping of the curvature of the cornea, eliminating defects like myopia, astigmatism and hypermetropia.
According to the defect, the cornea is given a different anterior surface. It becomes more curved when correcting hypermetropia, less curved or even concave when correcting myopia; irregularities of astigmatism are eliminated homogenizing the rays of curvature on the whole surface.
Correction is done by the laser according to a program worked out by a computer on the basis of the characteristics of the single eye, therefore according to a personalized program.
The result is predictable with differences of less than half a degree. It is highly improbable that the laser make a mistake. It has three safety systems on watch at the same time, ready to stop the ray in case of anomalous circumstances.
The procedure is now therefore extremely reliable; the only real cause of failure could be an incorrect evaluation on the part of the eye specialist about the information for the intervention.
Not all eyes are adapted to be corrected either because of improper structural characteristics or because of the presence of local or systemic pathologies, which can interfere on the healing process.

A visit to the eye specialist
It is therefore mandatory to have an examination done by an eye specialist who will examine in detail the characteristics of each eye: length, thickness, surface and curvature of the cornea, refraction, and at the same time general health condition as well as the family's medical history.
An adequate examination requires to instill collyrium into the eyes, which dilates pupils and blocks focus to see up close. No fear, everything comes back to normal after a few minutes. The eye specialist takes down the corneal surface's shapes and regularities by means of an instrument called a topographer, which consists in producing on the cornea of the patient a series of concentric light rings. A computerized optical system verifies the regularity and curvature of the rings from which it calculates curvature and regularity of the corneal surface.
Other ultrasound instruments measure the thickness of the cornea in various points. This exam is called pachimetry; moreover, ecobiometry is the evaluation of the length of the eye.
The excimer laser is then used. The computer connected to the laser, and having received the previous measurements, elaborates the corrective program. The program considers opening time and the route the laser must travel on the surface of the cornea to reshape it in a way to eliminate refractive errors. During the correction, the patient must keep a steady fixation and if the laser finds that the eye moves, it will automatically turn off.
The whole procedure lasts an average of a few seconds and is absolutely pain free since the ocular surface is desensitized with a few anaesthetic drops.
Immediately after the operation, a therapeutic contact lense is placed and the patient can leave the lab. Cortisone and antibiotic-based eye drops will be prescribed and will be used for many days in order to allow problem free healing of the treated corneal surface.
After the intervention, the following must be avoided:
- exposure to irritating agents like dust, smoke, wind;
- putting soap in the eyes during shower;
- swimming in a pool or the sea for 15-20 days;
- rubbing the eyes vigorously; protective lenses should always be worn.
There does not exit any contraindications to watch TV or look at a monitor; the entertainment is guaranteed.
If you have not thought about permanent make-up before surgery, you will have to do without it for a few days until the cornea is completely healed. For martial arts and boxing lovers, it is absolutely forbidden to receive any blows or punches on the eyes during 15 days.

Before the surgery
It is important that the eye be clean and uncongested and that the eyelids have no redness or little crusts. It is advised to use antiseptic soap for the hands and face during the days preceeding the surgery.
The mucous membrane, the conjunctiva, is impaired and fragilized by difficult digestion, agitated sleep and from exposure to irritating environments like smoke, dust and ultraviolet rays. In such case, post-surgical recovery may not be optimal. It is therefore advisable to follow a Franciscan or at least a healthy lifestyle during the preceeding and immediately following days of the intervention.

Various types of intervention

PRK: Reduction of myopia with excimer laser.
The objective of PRK is to eliminate or reduce the use of corrective lenses. It is achieved by modifying the cornea's curvature, which is flat in the centre: in this way, light rays from objects can focus clearly on the retina. The excimer laser vaporizes some of the cornea's layers. The quantity of corneal tissue eliminated determines how much myopia will be corrected.

Laser reduction of hypermetropia and astigmatism.
Thermokeratoplasty with an holmium laser consists in modifying the central curvature of the cornea, reshaping it. This is achieved when the holmium laser ray hitting the cornea creates a contraction and takes away the unwanted tissue.

LASIK: surgical treatment of myopia coupled with laser.
Also called Keratomileusis combined with excimer laser treatment, LASIK is a mixed intervention.
In fact, after having made an incision in the superficial layer of the cornea (epithelium) with a microkeratome, the central part is flattened by the laser.

What is the laser?
The laser is a uniform and powerful ray of light which can be produced in various ways. In ophtalmology, various types of laser are used in order to take advantage of the characteristics of each ray. The effect of laser radiation on the target can be of evaporation, incision or heat.

What is the excimer laser?
The excimer laser was developed at the end of the '70s and initially used to practice extremely fine incisions on printed circuits.
For use in the field of surgery, the produced light ray is controlled by a computer. It can remove microscopic parts of the tissue on which it is directed with extreme precision, since the ray's energy cuts the links between molecules and creates an evaporation of the target without damage to the surrounding tissues. The correction of refractive errors is done by bringing the superficial layers in the central part of the cornea, modifying directly the curvature and the optical power of the most important area of focus.