Photorefractive Keratectomy (PRK), also known as LASEK, is an alternative laser eye treatment for people with high prescriptions and thin corneas.
PRK is a highly successful procedure that takes about 5-10 minutes per eye, and while it does take a few weeks for your eyes to heal fully, it has the same success rate as LASIK, and almost all patients no longer have to wear glasses or contact lenses.
However, like any other surgical procedure, PRK does have potential complications.
What Are The Risks Of PRK?
PRK risks include unpleasant but short-term, temporary side effects.
In rare cases, PRK carries long-term risks, such as over-correction, under-correction or vision regression, permanent dry eye, corneal haze, infection, scarring, and ectasia.
Fortunately, these risks are rare but can cause permanent damage and vision loss.
All surgical procedures have risks involved and come with the possibility of complications. Your eye surgeon will explain these before the surgery and note that short-term effects and longer-term risks are involved.
Your surgeon should also explain post-operative care to help you avoid these risks.
First, it’s helpful to understand what happens during PRK so that the risks make sense.
Why Does PRK Involve Risks?
Laser surgery was developed to correct refractive problems of the eye.
Refractive problems occur if your eyes don’t bend light correctly, and you struggle to focus and see objects clearly. The main part of your eye involved in refraction is the cornea, the clear front window of the eye. The cornea is responsible for two-thirds of your eye’s total focusing power.
There are three primary forms of laser surgery used to reshape the cornea:
- PRK (photorefractive keratectomy), which is also commonly known as LASEK, and
- LASIK (laser-assisted in situ keratomileuses)
- Lenticule extraction (laser brand names include SILK, CLEAR, SMILE, and SmartSight)
PRK and LASIK are the most common procedures worldwide, although you will see lenticule extraction appearing more during the 2020s as the technology develops.
All three procedures have very similar results; however, lenticule is restricted in the kinds of prescriptions it can correct at the time of writing this article (it cannot yet treat long-sightedness or offer customised treatments).
LASIK and PRK are similar laser eye surgeries that use an excimer laser to reshape the cornea to improve vision.
The main difference is the way the laser accesses the cornea.
In PRK, the surgeon removes the surface skin layer of the cornea before performing the laser correction. In LASIK, a flap is created on the cornea’s surface, and the laser reshapes the tissue underneath the flap.
PRK and LASIK risks are the same as any challenges caused by surgery: pain, infection, scarring, and reduced success.
How do these risks manifest with PRK?
Short-Term PRK Risks
As your eyes heal, you risk experiencing short-term side effects. These are not long-term complications: they typically last for several days to months. Almost all patients have resolved any issues by 12 months after treatment.
It may take up to three months to get the full visual benefit from PRK and for your vision to stabilise without needing glasses, whereas the healing time for LASIK is much shorter.
The following short-term PRK risks tend to resolve as your eye heals.
While the procedure is not painful, PRK results in mild to moderate pain for three to five days post-surgery. Your eyes may feel irritated and gritty, and more watery than usual.
Think of how it feels when a scrape is healing on the surface of your skin; PRK has a similar impact on your eye as it has removed the epithelial layer.
The surgeon will usually prescribe pain medication, and a strict regimen of eye drops to ease the symptoms.
If pain and discomfort persist, visit the eye surgeon immediately to rule out infection.
A typical short-term risk of both PRK and LASIK is dry eye, where the eyes are irritated and gritty. You may have the unpleasant sensation of a foreign body in your eye.
A mixture of factors, including pre-existing dryness, increased tear evaporation, poor tear production and inflammation, causes dry eye.
This condition lasts several months and can typically be treated with eye drops. Most cases of dryness have resolved by six months after PRK surgery.
For the first 72-96 hours after PRK, your eyes will be very sensitive to light and remain sensitive while healing.
Exposed nerve endings cause this side effect following the removal of your cornea’s top skin layer (epithelium); this will resolve as the epithelium heals.
Avoid sunlight for the first 72 hours, wearing sunglasses and a wide-brimmed hat. Exposure to bright light can damage your newly formed corneas and cause permanent scarring.
Long-Term PRK Risks
In a small minority of cases, patients experience long-term complications due to PRK.
These can range from annoyance to severe implications such as loss of vision. However, these risks are very rare.
The most common risk associated with any laser refractive surgery is an under-correction.
Under-correction means that as the eye heals, some short-sightedness remains. You will not enjoy the full potential of PRK, and your improvement in vision may not be satisfactory.
The good news is that a second procedure can enhance under-correction. The small amount of short-sightedness that remains can be removed with a secondary laser correction. The original fee usually covers this.
In complex cases, such as where the cornea is thin, some surgeons aim for under-correction, meaning they do not reshape the cornea as extensively as possible.
Another PRK risk is overcorrection.
Overcorrection occurs when the eye heals with a more significant effect than intended. It is often a normal part of the variation within the healing process.
The procedure’s result may be unsatisfactory, and your vision will not improve as you hoped.
Again, as with under-correction, your doctor can usually treat overcorrection with a second laser enhancement procedure. Most ophthalmologists will wait six months or longer, as over-correction may settle and resolve by itself.
A shared PRK and LASIK risk is refractive regression. There can be more regression with PRK than with LASIK for larger prescriptions.
Refractive regression means that your vision improves and is initially clear. However, after about six months to a couple of years, some of the attempted correction is lost. Usually, most of the benefit remains as regression tends to be partial.
The following could cause regression:
- Rapid changes in young people’s eyes
- Corneas that underwent a high level of correction
- An abnormal healing process
- Pregnancy or endocrinal changes
- Biomechanical changes in the cornea
These causes are beyond the surgeon’s control and are not caused by an error during PRK.
Topical steroids and an enhancement procedure can treat regression, but some cases of refractive regression cannot be prevented entirely. Very high prescriptions tend to get some deterioration over the years.
ICL can be a better treatment for high degrees of short-sightedness.
In mild regression cases, glasses or contact lenses may help restore vision.
Permanent Dry Eye
Dry eye is a typical short-term side-effect of laser surgery. Unfortunately, there is a risk with PRK and LASIK that the eyes remain irritated and dry for extended periods.
In rare cases, dry eye is severe. It can be permanent, with eyes remaining dry, irritated, gritty, and intermittent tearing, resulting in blurred vision.
This condition usually develops in people with pre-existing dry eye conditions or lid disease.
Tear supplements and eye drops can ease symptoms.
Your vision can be blurred, cloudy, and hazy after PRK or LASIK. You may see haloes, glare, and starbursts, especially at night.
This condition is mainly caused by irregularity in the healing epithelial skin layer during the first days to weeks.
A much rarer condition is called corneal haze, a fine opacity near the surface of your cornea. It is caused by the production of a fine sheet of scar tissue in the weeks or months following treatment.
Corneal haze is usually triggered by exposure to ultraviolet light from the sun during the healing phase.
Corneal haze is usually mild and temporary, lasting two to 12 months until the cornea heals.
Corneal haze is very rarely seen these days, as many ophthalmologists will apply mitomycin C (MMC) during the PRK procedure. MMC has virtually eliminated corneal haze as a post-operative problem in PRK.
If corneal haze persists, see your opthalmologist, as further laser treatment can often remove surface scarring.
Ophthalmologists are not sure why people develop this condition but have identified the following risk factors for developing long-term corneal haze:
- High level of myopia or astigmatism being treated
- Pre-existing autoimmune conditions
- Overuse of anti-inflammatory drugs
- Exposure to UV radiation (e.g., not wearing protective eyewear in the sun).
While short-term corneal haze can be treated with topical steroids, and most cases spontaneously resolve, late-onset corneal haze can be tough to treat, and in extreme cases, it can lead to visual impairment.
A serious PRK risk is an infection, which fortunately only occurs in 1 in 7,000 cases. It is even rarer with LASIK, at about 1 case per 20,000 procedures.
An infection will show up within a week of surgery and can lead to scarring of the cornea and loss of vision.
Any pre-existing condition, such as dry eye syndrome, blepharitis (inflamed eyelids), or inflamed tear ducts should be treated before laser surgery.
Infection can also occur after surgery because of the following:
- Overuse of corticosteroids
- Improper application of antibiotics
- Exposure of the eye to unsterile water
- Traumatic event to the eye (e.g., something hitting the patient in the face).
Contact your doctor immediately if there are any signs of infection, such as inflammation, redness, swelling, pus, or fever.
Antibiotics can eradicate almost all cases of infection.
Infection usually leaves behind a small scar. The visual impact will depend on the scar’s location.
Peripheral scars will not affect vision, but central corneal scars can cause severe deterioration in the patient’s sight.
Please note that corneal scars are far more common from contact lens-related infections than from laser eye surgery.
Corneal scarring is a dangerous PRK risk, where scar tissue develops on the cornea. Fortunately, this is a rare complication.
Corneal scarring can be caused by surgery or by an infection.
Healing after PRK means that the epithelial cells grow back, which usually takes a week. However, in some cases, scar tissue and lesions can develop, obscuring the patient’s vision.
Symptoms of corneal scarring are blurred and cloudy vision, red, gritty, watery eyes, vision changes, and intense pain. These symptoms may initially be the usual side effects of laser surgery, but they should not persist for more than a week.
You can get prescription glasses or contact lenses to correct your vision, depending on how bad the corneal scarring is.
Further laser surgery can sometimes remove some scar tissue, so long as it is shallow. However, a corneal transplant will be necessary in extreme cases where the scarred cornea is replaced with healthy donor tissue.
A rare risk of PRK is corneal ectasia, where the cornea becomes uneven, alternately bulging and thinning, worsening the patient’s vision.
Fortunately, ectasia is now very rare due to improved scanning technology. 3D scanners allow doctors to detect even very minor tendencies to corneal weakness, usually genetically acquired, known as keratoconus.
In the UK, keratoconus occurs in around 1 in 400 people.
Symptoms of corneal ectasia include blurred and distorted vision, sudden worsening of vision, light sensitivity, and itchy eyes.
The treatment for keratoconus and corneal ectasia includes prescribing rigid, gas-permeable contact lenses, fitting intracorneal rings to reshape the cornea, and corneal cross-linking treatment. In severe cases, the patient will require a corneal transplant.
Collagen cross-linking has revolutionised the treatment of corneal ectasia and keratoconus, and corneal transplants for ectasia have become much less common.
Like all surgery, PRK carries risks.
Most patients experience temporary pain and discomfort post-surgery with PRK, but more serious risks include over-correction, under-correction, vision regression, permanent dry eye, cloudy vision, or infection.
These risks may cause scars, a misshapen cornea or, in extremely rare cases, loss of sight. However, you should be aware that vision loss is more common with contact lens use than laser eye surgery, so the risks need to be balanced.
If you’re considering PRK, schedule your free telephone consultation, and a member of our team will be in touch with you to discuss the potential risks of the procedure and advise you in more detail.