Photorefractive Keratectomy (PRK)
What is Photorefractive Keratectomy?
Photorefractive Keratectomy, or PRK, is a type of laser eye surgery for people who suffer from nearsightedness (myopia), farsightedness (hyperopia), or astigmatism. It is similar to LASIK in that it involves using an excimer laser to reshape the cornea to minimize or eliminate your dependence on eyeglasses or contact lenses. It is different from LASIK in that the eye surgeon does not need to use microkeratome (blade) or laser to make a flap from under which corneal tissue can be removed; instead the surgeon applies the laser directly to the surface of the cornea to achieve the desired vision correction.
PRK is well suited for people with thin corneas or certain other corneal abnormalities, for whom making a flap may not be the best approach. Also, PRK is the approved procedure for those in active combat and certain other positions in the United States military. PRK has been approved by the FDA for myopia since 1995 and for hyperopia since 1998, and it has an excellent safety record. To correct myopia with PRK, the steep cornea is made flatter by removing tissue from the center of the cornea. To correct hyperopia, the flat cornea is made steeper by removing tissue from the outer edges of the cornea. To correct astigmatism, the cornea is transformed into a more spherical shape.
PRK vs LASIK
Although these two procedures are similar, there are several differences between them. Much like LASIK, photorefractive keratectomy involves reshaping the cornea. Unlike LASIK, which involves removing tissue from the inner layers of the cornea, PRK applies laser energy to more superficial layers of the cornea.
As noted above, PRK is unlike LASIK eye surgery in that it does not require creating a flap (which entails certain risks). Some drawbacks still remain, however. There is usually more discomfort after PRK, and the recovery period is typically weeks, rather than days. Blurry vision and light sensitivity are common for up to a week or more following PRK surgery, whereas LASIK patients typically find these visual disturbances only last for the first few days following treatment.
Fortunately, multiple studies have shown that once patients have healed (six to twelve months after surgery), results from LASIK and PRK are equally successful.
The Photorefractive Keratectomy Procedure
Before surgery the doctor will carefully review your eye health and medical history. Then you will need to have a refraction test to measure your actual prescription. The shape of the surface of your eyes will be mapped with an instrument called a corneal topographer. Finally, the thickness of your cornea will be measured using an instrument called a pachymeter.
On the day of your surgery, the technician will put a series of antibiotic and anesthetic drops in your eyes in order to prepare them. These drops will help to prevent any possibility of infection and will numb the cornea so that you are comfortable during your treatment. The technician will clean the area around your eyes with a hygienic, gentle cleansing pad. A device called a speculum will be gently placed between your eyelids to keep your eyelids open.
Next the epithelium, the thin protective layer that covers the cornea, is removed. Since you have had numbing drops placed in your eyes, this will not be uncomfortable, but you will feel a slight pressure around your eyes. The surgeon will instruct you to look at a small light during your procedure. Today’s laser technology uses a tracking system that follows your eye movements during your procedure, so if you move your eyes a little it isn’t a problem. If your eye moves too much, the laser stops. Then, once you fixate on the small light again, the surgeon resumes the laser treatment.
To correct nearsightedness, farsightedness, or astigmatism, your surgeon will use an excimer laser. The excimer laser is programmed based on calculations made from the measurements taken during your consultation. The laser emits tiny pulses of light to predetermined positions on your cornea in order to reshape it. The eye surgeon has full control of the laser and monitors its position on the cornea. There is also a tracking system monitoring the position of your eye in order to make sure the beam is in the correct place. The application of the laser usually takes less than a minute per eye, depending on the complexity of the correction you need. A soft bandage contact lens is usually placed over the eyes to help reduce discomfort after the procedure.
The technician will often put additional eye drops in your eyes after the procedure is finished in order to soothe any irritation you may feel. Most often a protective clear plastic shield resembling a pair of safety glasses will be applied to prevent you from rubbing your eyes, or in case you get bumped accidentally. Pay careful attention to your doctor’s detailed instructions regarding additional drops to use at home and when to return for your first follow-up visit.
You will need someone to drive you home. When you get home, you should take a long nap. When you awaken, you will notice a dramatic improvement in your vision, which will most likely get even better within a few days as your eyes continue to heal. You should expect to feel some mild “grittiness,” as if a little sand or dust has gotten into your eyes. This is normal and should last a few days. As your eyes heal, it is normal to be a little sensitive to light, and perhaps to see some glare or even haloes around lights at night. This too will diminish as your eyes heal. Three to four days after PRK surgery, you will return to your eye doctor so he or she can remove the bandage contact lens. Typically, the epithelium will have regenerated by this time. Additional healing tips after PRK surgery include:
- Avoid touching or rubbing your eyes
- Avoid getting water in your eyes
- Follow your doctor’s instructions correctly for all medication doses
- Rest for the remainder of day after surgery, and possibly for the next 48 hours following surgery to ensure proper healing of the epithelium
- Avoid strenuous exercise for up to one week
- Call your doctor immediately if problems or complications arise
Photorefractive Keratectomy Candidates
Those best suited for photorefractive keratectomy are people with moderate levels of myopia, hyperopia, or astigmatism who have corneal abnormalities—such as a thin cornea—that make them unsuited for LASIK. Up to 95 percent of myopic people qualify for PRK surgery. Still, there are several criteria that must be met:
- At least eighteen years old
- Normal ocular health
- Not pregnant or breastfeeding at time of surgery
- Realistic expectations of final results
- Between -1.00 to -12.00 diopters of myopia
- Stable refractive error correctable to 20/40 or better
- Few or no allergies, especially ones that may lead to dry eye (e.g., pollen)
Certain medical or ocular conditions and medications may prevent PRK from being performed safely. These include:
- Certain medications such as Accutane (isotretinoin)
- Autoimmune conditions such as lupus or rheumatoid arthritis
- Severe corneal thinning, dry eyes, or irregular corneal surface
The Cost of PRK Surgery
The cost of PRK surgery is comparable to the cost of LASIK eye surgery ($1,500 to $2,500 per eye). Unfortunately, photorefractive keratectomy surgery is considered an elective procedure, and as such is usually not covered by vision insurance. However, many people are able to lower the cost of their PRK surgery by setting up a Health Savings Account (HSA) through various programs offered by banks or employers. Financing programs may also be available through the refractive surgeon performing the surgery. Talk with your eye care professional about such plans to help you reach your vision goals.
Photorefractive Keratectomy Advantages
PRK has several advantages over other types of laser eye surgery. These include:
- Better for thin corneas
- Good for mild to severe myopia, hyperopia, or astigmatism
- Good for people in restricted areas of military service
- Almost all myopic patients qualify for this procedure
- Approximately 90 percent of PRK patients come out with 20/20 vision and do not need eyeglasses or contact lenses one year after surgery; 95 to 98 percent have 20/40 vision or better without eyeglasses or contacts
Photorefractive Keratectomy Disadvantages
Depending on the patient’s overall health and degree of refractive error, disadvantages of PRK surgery may include:
- Longer healing time
- Longer time before results become apparent
- One to three days of discomfort following surgery
- High cost
- In rare cases medicated drops may need to be used for up to six months following surgery to prevent or reduce corneal haze or scarring
Complications of PRK Surgery
Possible complications of PRK surgery may include:
- Dry eyes
- Infection following surgery
- Corneal haze or scarring
- Incomplete or inaccurate vision correction
- Vision problems such as blurry vision, halos, or glare
Talking to Your Eye Doctor
Photorefractive keratectomy has become less common because of the success of LASIK. However, it is still used when LASIK is not the best choice. As with all laser surgery, there is risk, and side effects like light sensitivity and halos may not go away. It is important to talk with your eye care doctor about the risks in your specific case. Here are some questions to ask your eye care professional about PRK:
- After the surgery, what complications should I watch for that may indicate healing is not going well?
- Which do you think would be better for me, PRK or LASIK?
- What do you like about PRK compared to other types of eye surgeries?
- Am I a good candidate for this procedure? If not, what are my treatment options?
- How long will I need to rest following the procedure? When will I be able to drive and resume my normal activities?
- Will you be performing the procedure or do I need a referral?
- M. Beers, MD “The Merck Manual of Medical Information” Second Home Edition (Pocket Books, 2003) 1289
- J. Weizer, MD, J. Stein, MD, MS “Reader’s Digest Guide to Eye Care” (Quantum Publishing Ltd, 2009) 41-42
- E. Burns, MD “Collins Medical Dictionary and Health Guide” (HarperCollins Publishers, 2006) 291
- Refractive Surgery News, PRK Laser Eye Surgery: LASIK Without a Flap http://www.lasiksurgerynews.com/news/PRK-photorefractive-keratectomy.shtml