Why and when should PRK surgery be performed?
PRK (photorefractive keratectomy) is a type of refractive surgery to correct myopia (nearsightedness),hyperopia (farsightedness) and astigmatism. PRK was the first type of laser eye surgery for vision correction and is the predecessor to the popular LASIKprocedure. Though PRK recovery takes a bit longer than recovery from LASIK دارد. eye surgery, PRK is still commonly performed and offers advantages over LASIK for some patients.
Like LASIK and other types of laser eye surgery, PRK works by reshaping the cornea using an excimer laser, allowing light entering the eye to be properly focused onto the retina for clear vision. The main difference between PRK and LASIK is that in LASIK surgery a thin, hinged flap is created on the cornea to access the treatment area, whereas in PRK the cornea’s entire epithelial (outer) layer is removed to expose the area and no flap is created. For both PRK and LASIK, the excimer laser then sculpts the stromal layer of the cornea to correct your refractive error.
A variation of PRK, called لیزک یا LASEK , also is available. Instead of removing the outer epithelial layer of the cornea as with PRK, LASIK LASEK involves lifting the epithelial layer (using a surgical instrument called a trephine), preserving it during surgery and then replacing it on the eye’s surface at the end of the procedure. LASEK has decreased in popularity due to the slower recovery of vision compared with PRK, as the replaced epithelial layer takes longer to recover in LASEK than the growth of a new epithelial layer in PRK.
PRK VS. LASIK
The final results of PRK surgery are comparable to LASIK outcomes, but initial PRK recovery is slower because it takes a few days for new epithelial cells to regenerate and cover the surface of the eye.
There also is a slightly increased risk of eye infection and haziness of vision in the first few days after surgery. LASIK patients generally have less discomfort, and their vision stabilizes more quickly, whereas vision improvement with PRK is gradual and the final outcome can take several weeks. PRK does, however, offer some distinct benefits. Because PRK surgery does not create a corneal flap (which contains both epithelial and the deeper stromal tissues), the entire thickness of the underlying stroma is available for treatment. This is of particular benefit if the cornea is too thin for LASIK or if you have undergone LASIK previously and therefore have a thinner residual cornea. There also is no risk of flap complications, and the risk of removing too much of the cornea with the excimer laser is reduced.
How is PRK performed?
First, your eye surgeon removes a central area of corneal epithelium with an alcohol solution, a “buffing” device or a blunt surgical instrument. Next, an excimer laser is used to precisely reshape the curvature of your cornea’s surface. This computer-controlled, highly specialized laser delivers pulses of cool ultraviolet light that remove microscopic amounts of tissue in a precise pattern. A soft contact lens “bandage” is then placed on the cornea to help protect your eye. New epithelial cells grow back in five days typically, after which the bandage contact lens is removed by your eye doctor.
What to expect from PRK surgery
You must first choose an eye surgeon experienced in PRK surgery. You will then undergo a thorough eye exam to ensure your suitability for laser eye surgery. This will include an evaluation of:
- The size of your pupils.
- The moistness of your eyes, to evaluate the risk of developing dry eyes after laser eye surgery and treat accordingly.
- Corneal curvature, using a corneal mapping device to precisely measure the contours of the front surface of your eye.
- Corneal thickness.
Your eye doctor also will assess your general health and medical background, as well as any medications you are taking, to determine if you are a suitable candidate. If you wear contact lenses, you may need to stop wearing them for a period of time before your eye exam, as contacts can change the natural shape of your cornea. (Ask your eye doctor for specific advice about this.)
PRK eye surgery is an ambulatory procedure, meaning it is performed on a walk-in, walk-out basis. In fact, the actual surgery generally takes only 15 minutes. You will be awake during the procedure, but your eye surgeon may give you a mild oral sedative to help you relax.
Numbing eye drops are applied to your eyes, and an instrument called a lid speculum is used to keep your eyelids open. Your surgeon then directs the excimer laser over your eye, which is programmed for your exact prescription. You will be asked to look at a target light for a short time while your surgeon watches your eye through a microscope as the laser sends pulses of light to your cornea. The laser energy removes microscopic amounts of tissue and reshapes the cornea. Most people do not feel any discomfort, although you may feel some pressure on your eye. Your surgeon has full control of the laser and can turn it off at any time. PRK is performed on each eye separately (often one after the other on the same day), with each procedure taking only about five minutes. While some patients have both eyes treated on the same day, others choose to have the surgery on their second eye a week or two later. Your surgeon covers the treated cornea with a bandage contact lens. Within days, new epithelial cells grow back, and the bandage contact is removed.
You will be asked to rest for a short period after your surgery, after which you can return home (someone else must drive you).
Your surgeon will prescribe topical antibiotics as well as anti-inflammatory and pain medications to reduce post-operative discomfort, minimize any swelling and expedite healing. As with any other surgery, it is imperative that you follow your doctor’s instructions to help ensure optimum results.
You will need to attend frequent follow-up appointments with your doctor over the next several weeks to monitor the healing process. PRK recovery takes longer than recovery from LASIKsurgery. It may be days or a couple of weeks before your eyesight improves, and even longer for your vision to stabilize. Most PRK patients usually can resume driving a car one to three weeks after surgery, but it can take three to six months before vision is completely clear and stable.