The cornea is a part of the eye that helps focus light to create an image on the retina. It works in much the same way that the lens of a camera focuses light to create an image on the film. The bending and focusing of light is also known as refraction. Sometimes the shape of the cornea and the eye are not perfect and the image on the retina is out-of-focus (blurred) or distorted. These imperfections in the focusing power of the eye are called refractive errors. There are three primary types of refractive errors: myopia, hyperopia and astigmatism. Persons with myopia, or nearsightedness, have more difficulty seeing distant objects as clearly as near objects. Persons with hyperopia, or farsightedness, have more difficulty seeing near objects as clearly as distant objects. Astigmatism is a distortion of the image on the retina caused by irregularities in the cornea or lens of the eye. Combinations of myopia and astigmatism or hyperopia and stigmatism are common. Glasses or contact lenses are designed to compensate for the eye's imperfections. Surgical procedures aimed at improving the focusing power of the eye are called refractive surgery. In LASIK and PRK surgeries, precise and controlled removal of corneal tissue by a special laser reshapes the cornea changing its focusing power.
Photorefractive Keratectomy or PRK is used to reshape the cornea. PRK was the first surgical procedure developed to reshape the cornea, by sculpting, using a laser. Later, LASIK was developed. The same type of laser is used for LASIK and PRK. The major difference between the two surgeries is the way that the stroma, the middle layer of the cornea, is exposed before it is vaporized with the laser. In PRK, the top layer of the cornea, called the epithelium, is scraped away to expose the stromal layer underneath. In LASIK, a flap is cut in the stroma
If you decide to go ahead with LASER refractive surgery, you will need an initial or baseline evaluation by your eye doctor to determine if you are a good candidate.
If you wear contact lenses, it is necessary to stop wearing them before your baseline evaluation and switch to wearing your glasses full-time. Contact lenses change the shape of your cornea for up to several days or weeks after you have stopped using them, depending on the type of contact lenses you wear.
You should tell your doctor about your past and present medical and eye conditions, all the medications you are taking, including over-the-counter medications and any medications you may be allergic to.
Your doctor performs a thorough eye exam and discuss whether you are a good candidate, what the risks, benefits, and alternatives of the surgery are. You have the opportunity to ask your doctor questions during this discussion. Give yourself time to think about the risk/benefit discussion, review any informational literature provided by your doctor, and ask if you have any additional questions before deciding to go through with surgery and before signing the informed consent form. The day before surgery, you should stop using creams, lotions, makeup and perfumes. These products as well as debris along the eyelashes may increase the risk of infection during and after surgery
The surgery takes less than 20 minutes. You will lie on your back in a reclining chair under the laser machine. The laser system includes a large machine with a microscope attached to it and a computer screen.
A few anesthetic drops will be instilled in your eye, the area around your eye will be cleaned, and an instrument called a lid speculum will be used to hold your eyelids open. For LASIK procedure, a suction ring will be placed around your cornea to fix your eye and let the microkeratome to move over your cornea . Your vision will dim while the suction ring is on and you may feel a little pressure and experience some discomfort during this part of the procedure. The microkeratome and the suction ring are then removed. You will be able to see, but you will experience fluctuating degrees of blurred vision during the rest of the procedure. The doctor will then lift the flap and fold it back on its hinge, and dry the exposed tissue. The microkeratome and the suction ring are not used in PRK.
The surgical microscope will be positioned over your eye and you will be asked to stare at a light. This is not the laser used to remove tissue from the cornea. This light is to help you keep your eye fixed on one spot once the laser comes on. When your eye is in the correct position, your doctor will start the laser. During laser application you may become aware of new sounds and smells. The pulse of the laser makes a ticking sound. As the laser removes corneal tissue, some people have reported a smell similar to burning hair. A computer controls the amount of laser energy delivered to your eye. Before the start of surgery, your doctor will have programmed the computer to vaporize a particular amount of tissue based on the measurements taken at your initial evaluation.
If you have undergone PRK, a bandage contact lens is placed on your cornea, which will be remove in a few days after your corneal surface has been healed.
Immediately after the procedure, your eye may burn, itch, or feel like there is something in it. You may experience some discomfort, or in some cases, mild pain and your doctor may suggest you take a mild pain reliever. Your are given one or more types of eye drops to take at home to help prevent infection and/or inflammation. You may also be advised to use artificial tears to help lubricate the eye Both your eyes may tear or water. Your vision will probably be hazy or blurry. You will instinctively want to rub your eye, but don't! Rubbing your eye could dislodge the flap, requiring further treatment. In addition, you may experience sensitivity to light, glare, starbursts or haloes around lights, or the whites of your eye may look red or bloodshot. These symptoms should improve considerably within the first few days after surgery. You should plan on taking a few days off from work until these symptoms subside. You should contact your doctor immediately and not wait for your scheduled visit, if you experience severe pain, or if your vision or other symptoms get worse instead of better. If you have had PRK, these symptoms may be more severe and you may need stronger medications for pain relief.
You should see your doctor within the first 24 to 48 hours after surgery and at regular intervals after that for at least the first six months. You should wait one to three days following surgery before beginning any non-contact sports, depending on the amount of activity required, how you feel, and your doctor's instructions.
To help prevent infection, you may need to wait for up to two weeks after surgery, or until your doctor advises you, before using lotions, creams, or make-up around the eye. You should also avoid swimming and using hot tubs or whirlpools for tow weeks. Strenuous contact sports such as boxing, football, karate, etc. should not be attempted for at least tow months after surgery. It is important to protect your eyes from anything that might get in them and from being hit or bumped. Sunglasses are very useful during first few months after surgery. Contact lenses for cosmetic reason should only be worn after getting the opinion of your doctor.
After surgery, your vision may fluctuate and it may take up to three to six months for your vision to stabilize. Glare, haloes,difficulty driving at night, and other visual symptoms may also persist during this stabilization period. If further correction or enhancement is necessary, you should wait until your eye measurements are consistent for two consecutive visits at least 3 months apart before re-operation. It is important to realize that although distance vision mayimprove after re-operation, it is unlikely that other visual symptoms such as glare or haloes will improve. Contact your eye doctor immediately, if you develop any new, unusual or worsening symptoms at any point after surgery.