PRK eye surgery: How photorefractive keratectomy differs from LASIK
PRK (photorefractive keratectomy) is a type of laser refractive surgery to correct myopia (short-sightedness), hyperopia (long-sightedness) and astigmatism.
PRK was the first type of laser eye surgery for vision correction and has been performed longer than LASIK which has now surpassed PRK in popularity. Though it takes a bit longer to recover from PRK than LASIK, PRK 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 without glasses or contact lenses.
The main difference between PRK and LASIK is the first step of the procedures.
In LASIK, a thin flap is created on the cornea with a microkeratome or a femtosecond laser. This flap is lifted to expose the underlying corneal tissue and is replaced after the cornea is reshaped with an excimer laser.
In PRK, the thin outer layer of the cornea (epithelium) is removed and discarded prior to reshaping the underlying corneal tissue with an excimer laser. After the surgery, the epithelium repairs itself (grows back over the corneal surface) within a few days .
PRK versus LASIK
Results of PRK surgery are comparable to LASIK outcomes, but initial PRK recovery is slower because the epithelial cells need 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 following PRK surgery.
LASIK patients generally have less discomfort, and their vision stabilises more quickly, whereas vision improvement with PRK is gradual and the final outcome can take several weeks.
PRK does, however, offer some distinct benefits.
As no LASIK-style corneal flap (which contains both epithelial and the deeper stromal tissues) is created during PRK, more corneal thickness is available for treatment. This is beneficial if your corneas are too thin for LASIK. There's also no risk of flap complications and the risk of removing too much of the cornea with the excimer laser is reduced.
The PRK procedure
There are three steps to a PRK procedure:
A central area of corneal epithelium is removed with an alcohol solution, a "buffing" device, or a blunt surgical instrument.
An excimer laser is used to precisely reshape the curvature of the cornea. This computer-controlled, highly specialised laser delivers pulses of cool ultraviolet light that remove microscopic amounts of tissue in a precise pattern.
A soft contact lens is placed on the cornea to protect the eye while new epithelial cells grow on the corneal surface. This process takes about four or five days, after which the contact lens is removed by your optometrist.
What to expect
Before PRK
You must first choose an eye surgeon experienced in PRK surgery. You will then undergo a thorough eye examination 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 topographer, (a mapping device) to precisely measure the contours of the front surface of your eye.
The thickness of your corneas.
Your optometrist will assess your general health and medical background, as well as any medications you are taking, to determine if you are a suitable candidate for PRK.
If you wear contact lenses, you may need to stop wearing them for a period of time before your eye test, as contacts can change the natural shape of your cornea. Consult your optometrist for details.
During PRK
PRK eye surgery generally takes only 15 minutes for both eyes. You will be awake during the procedure, but your eye surgeon may give you a mild oral sedative to help you relax.
Anaesthetic 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.
Your surgeon covers the treated cornea with a bandage contact lens. Within a few days, new epithelial cells grow back, and the bandage contact is removed.
Immediately after PRK
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, minimise any swelling and expedite healing.
You will need to attend frequent follow-up appointments with your doctor over the next several weeks to monitor the healing process.
Full recovery from PRK
It takes longer for your vision to recover after PRK compared with LASIK surgery. It may be days or a couple of weeks before you are satisfied with your visual acuity, and even longer for your vision to fully stabilise.
Most PRK patients usually can resume driving a car one to three weeks after surgery, but it can take up to three months before your vision is completely clear and stable.
Long-term PRK outcomes
Outcomes of PRK and LASIK are very similar. Most people achieve 6/6 vision (20/20) after PRK surgery, and nearly all patients achieve 6/12 (20/40) visual acuity or better.
If sensitivity to light is a problem after PRK, spectacles with photochromic lenses often can provide relief. Also, if you have minor residual refractive error after surgery, low-power prescription lenses with an anti-reflection coating often can sharpen your vision for activities like night driving.
PRK and LASIK complications are rare and can include infection and glare (starbursts or halos that are most noticeable when you're viewing lights at night, such as while driving).
While unlikely, you may need additional or enhancement surgery to improve your vision further or to correct a gradual worsening of your eyesight over time.
Progressive lenses will likely be required after PRK surgery once you hit your 40's, due to an age-related loss of near vision called presbyopia.
Page published on Wednesday, 18 March 2020
