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General Description
All forms of laser refractive surgery change the shape of the cornea to better focus light as a clear image on the retina. The Excimer laser achieves this by precisely and selectively removing microscopic layers of the cornea to steepen or flatten the cornea depending on the patient’s prescription. In essence, laser refractive surgery applies the correction of a contact lens permanantly on the surface of the eye. Several procedures utilizing lasers are currently FDA approved.
In Photorefractive Keratectomy (PRK), the laser sculpts the surface of the cornea directly removing the layers of cells. LASIK, on the other hand, seeks to keep these layers of cells intact by using a highly specialized tool to create a flap less than 0.2 mm thick. This flap is raised and the laser energy applied to the newly exposed surface of the cornea. The corneal flap is the repositioned and allowed to heal on its own.
LASIK vs Clear Lens Exchange (CLE) www.ophthalmologymanagement.com
Excimer laser PRK is done as an outpatient procedure. Anesthetic drops are placed on the eye to numb it prior to treatment. The patient lies flat on a surgical chair which is rotated under the laser. The lid of the eye to be treated is cleaned with an antiseptic swab, and the other eye has a light patch placed over it to prevent the patient from seeing double during the procedure.
The patient’s surgical procedure is programmed onto a special keycard. During the treatment procedure, the laser’s computer reads the keycard and calculates the appropriate amount of laser pulses to sculpt the cornea for each individual patient. A pre-treatment to the patient’s operative eye is performed by the laser to remove 90% of the cornea’s epithelium (the first layer of the cornea). Pre-treatment also allows the patient to adapt to the different noises and sensations produced by the laser. After pre-treatment, the doctor gently removes the remaining epithelial cells to prepare the surface for the refractive treatment.
The laser is now ready to sculpt (ablate) the appropriate shape and depth of layers off the cornea to achieve the final effect:
1. Nearsightedness - corrected by treating the central region of the cornea
2. Astigmatism - corrected by treating only one axis of the cornea.
3. Farsightedness - corrected by treating the outer region of the cornea.
The sculpting usually lasts between 30-60 seconds (however, the total time in the operating room is approximately 20 minutes). The sculpting is computer controlled by a shutter that opens and closes to control the power of the laser’s beam.
Excimer LASIK is done as an outpatient procedure. Anesthetic drops are placed on the eye to numb it prior to treatment. The patient lies flat on a surgical chair, and the eyelids of the eye to be treated cleaned with antiseptic swabs. Sometimes a plastic drape is used to help keep the eye sterile and to keep the eyelashes out of the surgeon’s way. The doctor or assistant also places a lid speculum in the eye to be treated, which helps the patient to keep the eye open. The surgical chair is then rotated under the microscope of the laser, so the surgery can begin.
First, an instrument called a suction ring is placed on the eye to make sure that the eye has enough pressure for the keratome to work properly. As the vacuum for the suction ring is turned on, the patient will hear the loud humming of the machine that creates the vacuum for the suction ring, and it will seem as if all the lights in the room have been turned out. The doctor checks the pressure in the eye, and if it is correct, the doctor places the keratome into the suction ring, and passes it across the cornea. This creates the corneal flap. The doctor turns off the vacuum, removes the suction ring and keratome, and then lifts the corneal flap out of the way. Now the laser can be aimed at the exposed surface of the cornea, to sculpt (ablate) the proper shape and depth.
After the Excimer laser treatment, the flap is replaced over the treated area. The lid speculum and drapes are carefully removed, and drops are placed on the eye to reduce discomfort and prevent infection. Because the corneal flap protects the area treated by the excimer laser, patients do not usually need a contact lens to reduce discomfort or promote healing. Also, the outer surface of the flap has not been treated, and is smooth and clear. This allows patients to have clearer vision sooner than they would have following PRK.
