Vision Correction Techniques

Lasik or PRK?
The original form of excimer laser treatment is known as PRK (for "photo-refractive keratectomy"). In PRK, the laser energy is applied to the surface of the cornea. The most popular variation of excimer laser treatment is called Lasik (for "laser in-situ keratomileusis"). In this technique, the laser applications are made within the cornea, rather than on the corneal surface. This is accomplished by creating a thin flap in the front of the cornea and then applying the laser treatment to the tissue beneath the flap.
When the laser treatment is applied to the tissue deep within the cornea instead of to the surface, the healing response is lessened, which greatly speeds up the vision recovery period. Patients usually see quite well the next day after Lasik, as opposed to waiting several weeks with PRK. Excessive haze, resulting from an abnormal healing response, is one of the primary complications which may occur in PRK, but is virtually non-existent in Lasik.
  
Most of the pain fibers in the cornea are in the surface portion. Because this portion of the cornea is removed in PRK but not in Lasik (it is part of the flap, which is folded back into place after the laser energy is applied), there is much less discomfort after Lasik.
  
Lasik requires an additional surgical step, which is the creation of the flap. The flap is created with an instrument known as a keratome, which cuts and then folds back a thin layer of the front of the cornea. Creation of the flap takes about 15 seconds and is painless.
  
Complications with the flap occur about 1% of the time. Almost all of the complications are mild and can be easily treated, often by lifting or repositioning the flap. The most serious complication would involve improper creation of the flap; when this occurs, the patient is asked to wait three months, and then can return for a repeat treatment.
  
Lasik is our procedure of choice. In fact, we have stopped performing all other techniques, except in very cases. Patients greatly prefer the Lasik procedure in terms of rapid vision recovery and decreased pain. The vision recovery with Lasik is so rapid that most of our patients return to work the very next day. Dr. Caster has performed thousands of Lasik procedures, and has had the Lasik procedure on his own eyes.

Radial Keratotomy (RK)
Radial keratotomy (RK) was the first surgical procedure to be widely used to correct nearsightedness. Radial keratotomy was invented in the Soviet Union in 1973 and was first performed in the United States in 1978. Because of the availability of excimer laser, RK is seldom performed today.
  
Like excimer laser surgery, RK can correct nearsightedness by altering the shape of the cornea. The doctor makes a series of incisions in the periphery of the cornea. This increases the corneal curvature slightly where the incisions are made, and decreases the curvature in the central portion of the cornea. The incisions are made in a radiating pattern, like the spokes on a bicycle wheel. By varying the number, length, depth and location of these incisions, different amounts of nearsightedness can be corrected.

Effectiveness of Radial Keratotomy
Radial keratotomy has been able to correct mild and moderate nearsightedness, up to about 6 diopters.  However, because excimer laser treatment is more accurate, RK is very rarely performed today.
  
Side Effects of Radial Keratotomy
All RK patients experience some side effects. They are most noticeable during the early healing phases, but in rare situations may be permanent.
Daily fluctuation is a shift in the vision toward nearsightedness as the day progresses. This occurs in all RK patients, but to a noticeable degree in about 10%. If significant, the patient may need to wear glasses for some nighttime activities, such as driving or watching a movie.
  
The star-burst effect is a star-like pattern of reflections, most noticeable when a bright light is viewed against a dark background. This effect is prominent during the healing phase and diminishes over time.
  
Light sensitivity is also prominent during the early healing phases. It usually quickly disappears, though rare patients can have persistent difficulties.

Complications of Radial Keratotomy
The most common complication of RK is under-correction or over-correction. Under-correction is treated by a repeat procedure, known as a "touch-up" or "enhancement" procedure. Over-correction, which results in farsightedness, usually must be treated with glasses or contact lenses. Fortunately, serious medical complications are very rare, but do occur. Serious complications include infections, irregular healing, and improper placement of the incisions.
Progressive hyperopia is a development of farsightedness (hyperopia) months or years after RK, and is more common in patients requiring large corrections.  Excimer laser techniques (Lasik and PRK) do not experience this problem at all.

Astigmatic Keratotomy (AK)
Astigmatic keratotomy (AK) is a variation of RK used to treat astigmatism. AK involves arc-shaped incisions in the cornea, whereas RK involves radial incisions (like the spokes of a wheel). AK is often performed in conjunction with RK. The side effects from AK are mild and healing is generally quick and easy. AK will diminish or eliminate astigmatism.  At the Caster Eye Center, we use the excimer laser to correct astigmatism, so AK is used very rarely.

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