What is Myopia (short-sightedness)? The usual cause is that your eyeball is too big: rather like a tennis ball compared with a golf ball! The cornea is the transparent window over the front of the eye. It is even more important than the lens in focusing light on the visual layer (retina) which lines the back of the eye. In Myopia light is focused in front of the retina.
How does the Excimer Laser Help?
It reduces the amount of your Myopia by shaving off a very thin portion of your cornea, thus making your cornea flatter and less powerful. Light will no longer be focused too far forward, but on your retina.
What is Hyperopia (far-sightedness)?
This is the opposite of Myopia. Your eyeball is too small.
How is Hyperopia Dealt With?
Your cornea is sculpted by the laser. More tissue is removed peripherally than centrally, which has the effect of steepening the central cornea and making it more powerful. Light is focused on the retina, and not behind it as was formerly the case.
What is Astigmatism? How is it Treated?
In this condition, there is a difference in the steepness of the cornea up-and-down compared to left-and-right. To take our sports ball example a little further, similar to a side-on rugby ball compared to a soccer ball!
Back to Top
Home
When Were PRK and LASIK First Performed?
Many millions of patients have now been treated with PRK throughout the world, since this was introduced in 1987. The idea was in developmental stages from the early 1980's, however. LASIK is a newer procedure introduced in the early 1990s but there have been many millions of patients treated with LASIK also.
What Are the Differences Between PRK, LASEK and LASIK ?
The excimer laser can be either applied to the surface of the cornea after the epithelial layer has been wiped off (PRK); or at a slightly deeper level, after a disc-shaped, hinged flap of cornea has been mobilized with a surgical instrument called a microkeratome (LASIK). The flap can also be produced by a laser (Intralase). The stronger your prescription, the more likely LASIK is to be recommended. LASEK is a modification of PRK in which the epithelial layer is softened with 20% alcohol solution before being laid back as a flap that is replaced at the end of the laser treatment
Is My Prescription Suitable For Laser Treatment?
Any glasses prescription can now be treated, but the two general rules are that the weaker the initial prescription the better the result, and the treatment of Myopia is more predictable than that of Hyperopia and Astigmatism. LASIK has greatly enhanced the results of more complicated treatments, however.
There are certain associated eye or whole-body diseases which mean that you cannot be treated, but those will be searched for during your pre-treatment consultation.
The very best results are obtained for Myopia of up to -6.00, unassociated with Astigmatism; there is a 97% chance that you will be allowed to drive without glasses, and a 78% likelihood of you reading the bottom line of the eye test chart There is in any case nearly a 100% chance of your final glasses prescription being better than that which you had before PRK, LASEK or LASIK. If the initial treatment does not fully eliminate your need for glasses, re-treatment (enhancement) is possible. However, enhancement is not usually necessary.
Back to Top
Home
Are PRK, LASEK and LASIK Problem-free Procedures?
Few things in life are problem-free! Here are some of the advantages and disadvantages or PRK versus LASIK:
- The surface treatment of PRK leaves the cornea inflamed. This results in a ‘healing haze’, which usually lasts for three to six months. The stronger the prescription being treated the greater will be the haze, and the more unpredictable the results, because haze leads to laying down of tissue and partial reversal of the treatment. The haze is not usually bad enough to impair vision, but can produce glare when driving at night. It is important to mention that Glasses and Contact Lens wearers also experience night glare, however. LASIK results in quicker visual rehabilitation because the deeper corneal treatment is not associated with healing haze. LASEK can be associated with healing haze because it is a surface corneal procedure, but probably less so than is the case with PRK.
- Haloes around lights are also possible with both PRK, LASEK and LASIK, but have nearly been eliminated by the larger treatment zones of recent years.
- The surgical procedure itself is more uncomfortable and also lasts longer with LASIK compared with PRK; but there is almost no pain after a LASIK procedure, whereas the pain after PRK is usually described by patients as mild to moderate (the treatment of post-PRK pain is very effective). LASEK post-operative pain is commonly greater than that associated with LASIK, but not as significant as that associated with PRK.
- Because LASIK is a more complex surgical procedure than PRK or LASEK, there are more possible complications directly related to the surgical procedure (such as surface epithelium growing under the LASIK flap). However, LASIK surgical complications are rare.
- It takes longer to completely recover from PRK and LASEK compared with LASIK, which means that more follow-up visits are likely to be required than PRK.
- Visual improvement is almost immediate with LASIK, but takes a week to two weeks to occur after PRK and LASEK.
- LASIK is sometimes found not to be possible at the time of surgery, and under these circumstances PRK or LASEK will be performed instead.
- Other complications are possible, but rare.
Back to Top
Home
I Cannot Decide! Would you Recommend That I Choose LASIK, rather than PRK or LASEK, Doctor?
Here are some guidelines for you based on your initial glasses prescription. It must be stressed that these are only guidelines:
- In Myopia and Hyperopia, LASIK will be recommended, usually, rather than PRK or LASEK. This is especially true for Hyperopia....
- ....however, there are some situations in which PRK or LASEK will be the better choice, such as if your corneas are unusually thin.
- The larger your Astigmatism, the higher the chance that LASIK will be recommended.
Back to Top
Home
PRK, LASEK or LASIK Can Correct My Distance Vision, But Can They Also Worsen My Reading Vision?
Unfortunately, yes, if you are in your mid 40’s or older because the lens in the eye becomes unable to change focus about that time. This is the case for anybody and not just for those who have an Excimer Laser procedure done; that is why you see people wearing Bifocals or Reading Glasses. You may be happy to be able to throw away your Distance Glasses in exchange for Reading Glasses; or you may prefer to have one eye purposely corrected for reading (which will leave you with somewhat blurry distance vision in the eye) so that you can use one eye to read whilst using the other eye for distance vision. The state of having one eye for distance vision and the other for reading is called ‘Monovision’.
If you are younger than 40-45, you do not have to consider the above information, unless you like to plan ahead – in which case you could have your second eye corrected for reading. Another consideration is having a further Excimer Laser procedure when you reach 40-45 to steepen one of your corneas to give you a reading eye again.
My Present Glasses Prescription Has Had to Be Strengthened Recently. Does This Matter?
This means that your eye has not yet finished growing. As PRK, LASEK and LASIK do not prevent further lengthening, you should wait until the prescription stabilizes before being treated with Excimer
Laser. On the other hand, a changing prescription does not absolutely prevent you from going ahead, because PRK, LASEK or LASIK can be repeated.
Back to Top
Home
I Wear Contact Lenses. Do I Have To Stop Wearing Them For a Period Before My Pre-Treatment Consultation or Treatment?
Yes, please do not wear Hard (PMMA) Contact Lenses for at least 12 weeks. Do not wear Hard/Rigid Gas Permeable Contact Lenses for at least 4 weeks. Do not wear Soft Contact Lenses for 1 week.
Should I Bring Someone With Me at the Time Of My Laser Treatment?
Yes, because you could be drowsy after the treatment, there will be some discomfort, and you will not instantaneously get used to your new vision.
Back to Top
Home
What Does the Laser Treatment Involve?
It is done in a consulting room style rather than hospital operating room setting. No form of anaesthetic other than eye drops is necessary because the eye treatment is so superficial. You lie flat on your back looking up into an operating microscope. The size of the laser is about that of a large desk from which an overhead arm delivers the laser beam through the microscope as you look at a fixation light. The whole PRK procedure lasts about 15 minutes, with the laser beam being fired usually only about twice for 30 seconds on each occasion. LASEK usually lasts about 20 minutes, and LASIK is usually completed within 30 minutes.
Your other eye will have a shield placed over it during the treatment to protect it, and the procedure takes place so close to the treated eye that you cannot see clearly what is being done. If you have both of your eyes treated at the same time, the shield will be repositioned over the treated eye when the second eye is treated. You will be told when to expect the sound of the laser firing.
Although you will feel no pain during PRK, the first 24 to 48 hours afterwards are painful (mild to moderate pain) until the surface cells have healed again over the defect produced by the laser. Bandage soft contact lenses are usually used to assist PRK and LASEK pain. The pain after LASEK is often intermediate between that after PRK and LASIK. You will be given eye drops and tablets to relieve the pain; these are very effective. LASIK patients rarely experience any significant post-treatment pain.
When Can I Drive?
You should not do so until you no longer need pain medications and until you are beginning to get used to the change
in vision. Most people refrain from driving for about a week. You also should not drive for at least 24 hours if you have had to take a long-acting sleeping tablet on the first night.
Back to Top
Home
Can I Get My Second Eye Done?
If the eyes are to be treated separately, it is usual to wait several weeks for PRK and LASEK, and a couple of weeks for LASIK before treating the second eye. During this interval you may choose to wear a Contact Lens in the untreated eye, or to have a zero power lens put in your glasses for the treated eye. However, if you have an initial prescription stronger than about -3.00 or +3.00, it is likely that a zero power lens will make you see double because of the different image sizes in the 2 eyes, so it is not recommended in these circumstances... You may prefer just to enjoy the vision in your treated eye and go without correction for the eye awaiting laser treatment.
However, especially with LASIK, it is possible to have both eyes treated at the same time and will usually be offered as the better option.
Back to Top
Home
Copyright ©2009 Dr. Paul Cherry
This page last revised: March 19, 2009
One of the most experienced Excimer laser surgeons worldwide, having performed nearly 15,000 laser surgeries for the correction of mild, moderate and severe myopia or hyperopia with or without astigmatism. Has treated patients not only from Canada, but also from as far afield as the USA, Iran, the Canary Islands, Ireland, Finland, Luxembourg and Britain. In addition to PRK, performs LASIK, the procedure of choice for most patients.
