PRK is PhotoRefractive Keratectomy, a form of laser refractive surgery in which the shape of the cornea is changed using an excimer laser. The laser ablation is done on the surface of the cornea rather than under a flap as in LASIK. This is often called surface ablation and there are a variety of names and acronyms used depending on how the surface cells of the cornea (the epithelium) are removed to do the procedure. Transepithelial PRK is performed with the Schwind Amaris 1050 laser by using the laser itself to remove the epithelium. This results in faster healing and recovery times as well as making the procedure itself easier.
PRK is used rather than LASIK if someone’s cornea is too thin, if there are problems with the surface of the cornea, if there are superficial scars present, or for those doing serious contact sports. The vision results are as good as with LASIK but the postoperative recovery is slower and more time off work is required.
Modern laser refractive surgery is very safe and effective, with most people being extremely happy with the results. We commonly hear that it is the best thing people have ever done and that they wished they had done it years ago. It usually makes a huge difference to people’s quality of life.
You do need to be aware, however, that it is not perfect, despite what you may have seen or heard. Even though we use the most up-to-date technology and lasers there is some variability in the results and not everybody’s vision is perfect afterward. This is mostly because the procedure is performed on living tissue. Corneas are different in ways we cannot measure and react to the laser variably. Also, the healing responses afterward can alter results slightly.
What this means is that your unaided vision after PRK may not be quite as good as it is now with your glasses or contact lenses and it may not be possible for us to make it that good. Almost always the vision in one eye will turn out to be slightly better than the other when tested individually but most people are not aware of this with both eyes open.
We do expect to be able to make you able to function very well in most situations without glasses. People with high prescriptions may need to wear glasses in some situations, such as for driving at night. Those older than 45 years or so will still need glasses for near vision unless they have a monovision correction.
PRK is used rather than LASIK if someone’s cornea is too thin, if there are problems with the surface of the cornea, if there are superficial scars present, or for those doing serious contact sports. The vision results are as good as, if not slightly better than, with LASIK.
Not everybody can have, or should have, laser refractive surgery.
You may not be suitable if your spectacle prescription measurements are out of the range that can be corrected, or if your corneas are too thin, or have abnormal topography. There may be other issues with your eyes that may mean that it is not a good idea to have the surgery, for instance: severe dry eye, glaucoma, or retinal problems. We will usually not perform refractive surgery if one eye is significantly amblyopic (lazy). If there is any sign of cataract (opacity in the lens inside the eye) then it is not sensible to have laser refractive surgery. It does not work as well for long-sightedness (hyperopia) as it does for short-sightedness (myopia).
If you are very young or have a high correction we may advise waiting to be sure your refraction is stable. We will generally not treat those younger than 20 years and may advise waiting for those older than that depending on individual circumstances.
The surgery may not be able to achieve what you want it to do – most commonly this relates to being unable to improve near vision for people older than 45 years.
If you cannot accept that your vision may not be perfect afterwards then you should probably not do it. It is important that you have a reasonable expectation of what can be achieved so that you are happy with the result.
The laser procedure is performed as an outpatient procedure at Lions Eye Institute. You will be here for 1-2 hours. You will have some oral sedation and analgesia and will need someone to drive you home and to bring you back again the next morning.
PRK is basically the same as LASIK but without cutting a flap in the cornea, so it is easier to have done. It is more painful afterwards than LASIK and recovery of vision is slower. The laser part of the procedure is exactly the same as with LASIK, though.
The PRK procedure takes about 10-15 minutes and is performed with local anaesthetic eyedrops (the same as we use in the clinic). You will be lying down with your head in a shallow rest and a sterile drapes will be placed around the eye. The anaesthetic drops stop you feeling the need to blink and your eyes will be held open so that you cannot blink. The surface cells of the cornea (epithelium) are removed over an 8-9mm diameter area either directly with the laser or by loosening them with some fluid. The refractive change is then made directly on the surface with the Schwind Amaris 1050RS laser. This will take between 5 and 45 seconds. The laser tracks your eye movements during the treatment but it is important to keep as still as possible. A bandage contact lens is placed on the eye and stays for 3-10 days until the surface has healed.
The procedure is usually not painful but there are some unpleasant sensations, including some pulling and stretching of the eyelids and bright lights. Most people say it is not as bad as they expected.
These acronyms refer to different methods of dealing with the corneal epithelium during the procedure. There does not appear to be any significant difference in outcome between these various methods. The laser part of the procedures and recovery is the same.
At the end of the PRK procedure you will be able to see but not very well. Vision is very variable in the first few days to a week while the surface heals and usually gets worse at about 3 to 5 days as the surface heals in the middle of the cornea but then gradually improves over the next few weeks.
The contact lens is left in for 3 to 10 days until the surface has healed. You do not have to do anything with the lens, it just stays in there. Often, vision will be worse again briefly after the contact lens is removed as it takes some time for the new surface to smooth out.
You will probably need 1-2 weeks off work, depending what you do. It is more difficult if you have to do a lot of computer work, especially if you are working in an air-conditioned environment. This will all be worse for people who are older than 40 years.
The local anaesthetic we use wears off within an hour after the procedure and then your eyes will start to feel irritable and very light sensitive. You will find it very difficult to keep the eyes open and they will water for several hours afterwards. It is best to go home and rest with them closed for a few hours. You will be given some analgesic tablets (we use Panadeine Forte, so tell us if you cannot take codeine) and can take more of these, or any analgesic you are comfortable with, later. We advise taking regular Nurofen and/or Panadol regularly to keep ahead of the pain as it is often worse in the 2 days after the procedure.
There is not a great deal of restriction on your activity. It is fine to exercise but be careful about rubbing your eyes if you are sweating. Do not swim or use a spa for at least 2 weeks as this could introduce infection.
It takes 3 to 6 months for your refraction to completely stabilise after the procedure but most of the change happens in the first month. After this you should not be aware of any change in distance vision for a long time. The effect of the PRK surgery does not wear off but your eyes can continue to change with age. This is more likely the younger you are when you have it done, or for those who are very short-sighted to begin with, or for hyperopic (long-sighted) corrections. If your eyes do change then it may mean that glasses, or another laser treatment, may be necessary years down the track. This is less likely for those with lower levels of short-sightedness. In the very long run there will be changes in the lens inside your eye that may alter the focus when cataracts start to develop. That may then require cataract surgery.
Near vision usually starts to deteriorate in mid-to-late 40’s. When that starts it will be necessary to use glasses for near vision in some circumstances and the need for these will gradually increase as you get older. At present, we have no way of fixing this (presbyopia) completely.
PRK is a very safe procedure but there is a small risk of having problems either during the procedure or afterwards. These problems may just be a nuisance but some could permanently affect your vision or comfort:
It is possible that you might end up being over or under-corrected as far as the focus of one or both eyes is concerned. If you are aware of this and are uncomfortable with it then this can be retreated with more laser if everything else is satisfactory and there is enough thickness in the cornea. We generally wait for at least 6 months for the focus to be stable. Overall, about one in forty will need a retreatment but this is more likely for higher level corrections. There is no charge for this in the first year after the procedure.
Surface healing problems
The corneal epithelium usually heals within 3-5 days but in some cases this may take longer. The bandage contact lens may need to be replaced and left for longer. This may increase the time that it takes for vision to improve.
Everybody’s eyes are drier after the laser procedure. This is because the reflex production of tears is reduced by cutting through the nerves in the cornea. These nerves take 1-2 years to regenerate. Most people will not be aware of any problem with this but those who have dry eyes to start with and those who are older than 40 years are more likely to have some symptoms of dryness. It is more bothersome for people who use computers a lot and who work in air-conditioned offices. It may be necessary to use lubricating drops for some time after the procedure. It may help to take omega-3 fatty acid supplements (fish oil or flaxseed oil, 3,000mg daily, or Lacritec 3 capsules daily). If you have had any dry eye issues before then it helps to start using lubricating drops and omega-3 supplements before the laser treatment.
Haze and scarring
In some people the healing response in the cornea is overactive and haze can develop just beneath the surface. This is more likely with high level corrections. Usually this can be dealt with by using steroid drops for longer after the procedure. Rarely, the response can be so strong that a scar develops that limits vision. In that case further treatment may be required to remove the scar.
We use a drug called mitomycin C to inhibit the overactive healing response that causes scaring. This is applied to the surface of the cornea briefly after the laser treatment. The use of mitomycin reduces the chance of developing haze and scarring significantly. There are some potential problems of using mitomycin, though. It rare cases is can lead to thinning or perforation of the cornea or sclera and the very long term implications of using mitomycin are not known.
Haze is more likely to occur with exposure to high levels of ultraviolet light (at the beach, on water, or at high altitude such as when skiing). You should wear good sunglasses when outside, especially during the summer months.
It may help to take vitamin C as the antioxidant effect may reduce haze formation. Take 1 gram of vitamin C daily.
Infection can occur but is very rare and is usually treatable with the appropriate antibiotics. It could lead to scarring that would require corneal transplantation.
This refers to the cornea warping out of shape if it is made too thin by the laser procedure. If that happens then hard contact lenses are required to obtain good vision as glasses or soft contact lenses do not work well. There are some newer treatments for this problem but in severe cases corneal transplantation may be required. Subtle changes in the shape of corneas may suggest that this is more likely to happen and we look very carefully for any sign of this in your initial assessment. A family history of keratoconus is also a risk factor for this. We generally advise people in that situation not to have laser refractive surgery. This is less likely to occur with PRK than with LASIK.
Loss of best corrected vision
A few people will have poorer best-corrected vision after PRK. This means that the vision at best afterwards is not as good as it was before. Most people are not aware of this but occasionally someone will be aware that the quality of their vision is not as good as it was before. The important thing about this is that it is not correctable with glasses or contact lenses and may not be fixable with laser retreatment. This is more likely to happen with high level corrections.
Night vision problems
This was an issue in the early days of laser refractive surgery and with the old radial keratotomy procedure but it is rarely a problem now. Night vision does take longer to improve after the treatment but usually is as good as it was with glasses or contact lenses before.
There may be other problems that could affect your vision or ocular comfort after LASIK.
Once every year or two we will have a technical problem with one of the lasers on the day of surgery. That may mean that a treatment list, or part of a list, has to be postponed. That is a major nuisance for those affected but is unfortunately unavoidable even with the best regular maintenance.