Surgery Related Questions
Who is eligible for surgery?
A patient's refractive error must be stable for at least a year. For most people this happens between the ages of 18 and 21.
Children should never undergo LASIK or PRK surgery because they are still developing physically. Their astigmatism and short-sightedness are likely to be still increasing. Also, a child's healing response is likely to be more aggressive than an adults. This could lead to scarring or regression, especially in the case of PRK.
What are some conditions which prevent you from undergoing LASIK?
If you suffer from severe eye-related conditions such as myopic degeneration, macular degeneration, total retinal detachment and glaucoma you should not undergo LASIK.
What are some eye problems LASIK cannot treat?
One condition that cannot be treated by LASIK is cataract. Cataract is caused by the clouding of the lens of the eye. A cataract extraction with intraocular lens implantation is required.
Keratoconous, a very uncommon eye disease due to an irregularly thinned cornea, is another problem which prevents LASIK correction. Although Keratoconics essentially have normal-looking eyes, a corneal topography will reveal this unusual eye disease. Keratoconics suffer poor spectacle vision, frequently distorted by high astigmatism. They only obtain good vision with Rigid Gas Permeable (RGP) contact lenses. Many people suffering from this condition are likely to seek LASIK treatment.
What if I have small, deep-set eyes or any other condition that will obstruct the laser?
It is possible for all patients with small deep set eyes to have LASIK performed on their eyes. Some patients may require minor procedures to be done to make the eye suitable for LASIK surgery. Your doctor should discuss these procedures with you.
The new IntraLase® Femtosecond laser allows safer surgery for those with small, deep-set eyes.
What range of short- and long-sightedness can be treated using LASIK?
LASIK can be performed for powers ranging from 0.50 to 30.00 diopetres (50 to 3,000 degrees) for myopes and 0.50 to 6.00 dioptres (50 to 600 degrees) for hypermaetropia.
Correction is usually unnecessary for powers below 1.00 diopetres (100 degrees).
What factors determine the range and accuracy of treatment possible?
There are 3 main factors which affect how much and how accurate the treatment is.
The first factor is the thickness of the patient's cornea. The thicker the cornea is, the greater the amount of correction that can be achieved. Usually the remaining corneal bed must be at least 200 to 250 microns thick.
The second factor is the size of the patient's pupil in the dark. Larger pupils require deeper and wider treatments.
The flap does not contribute to the strength of the cornea. Most experienced LASIK surgeons try to make the flap as thin as possible. However if a flap is made too thin, it can buttonhole and the LASIK procedure has to be aborted. A thin flap maximizes the remaining cornea bed available for treatment.
Finally, the higher the power, the less accurate the correction. This is because more correction requires a larger amount of tissue to be ablated and a longer time of treatment.
Can I have both eyes treated at the same time?
Theoretically it is possible. Some surgeons do perform surgery on both eyes at the same time. Often this is for the surgeon's convenience.
However, doing one eye at a time (sequential surgery) allows a doctor to learn about patient's individual response to treatment, and this makes the second treatment more accurate, as shown in clinical research studies.
Although it may seem like a good idea to LASIK both eyes at the same time, it is necessary to consider things like infection. There is always a risk of bilateral infection when 2 eyes are operated on simultaneously.
At Jerry Tan Eye surgery, Dr Tan has never done bilateral simultaneous LASIK since he started performing LASIK in 1996. He believes in your safely first!
When can my second eye be treated?
If the first eye is of a low power, the second eye can be treated within one or 2 weeks after the first surgery. For eyes with moderate power, LASIK can be performed 2 to 3 weeks after the first surgery. For high myopes, visual stability must be achieved (usually around 4 weeks) before proceeding for the second surgery.
What is over-correction and under-correction? How can it be rectified?
As with any form of refractive surgery, there is a possibility of under- or over-correction in LASIK treatment. Individuals have different responses to the laser ablation, however most patients respond very similarly.
A specific amount of tissue removal is usually required to correct a specific amount of refractive error. The amount to be removed is derived from a surgeon's experience, laser calibration as well as collated statistics of LASIK procedures worldwide, and assumes that the patient follows the normal healing response.
An over-correction would mean that the patient has over-responded to treatment. This would mean that myopes (short-sighted) may become slightly hypermaetropic (long-sighted) and vice versa. An under-correction would mean that the patient under-responded to the correction. This would mean that the person's myopia or hypermaetropia may still exist but albeit in a much smaller amount.
Over- and under-correction can occur to anyone whose healing response may vary from the norm. Fortunately, these conditions can be rectified via enhancements.
Enhancements can be performed up to 6 months after the initial surgery and after this period, the flap will seal back to its original bed and usually can no longer be opened.
What happens during enhancements?
When an enhancement is performed, a special instrument is slipped below the flap and the flap is lifted without the need for cutting. Correction of residual refractive error is then performed.
Enhancements tend to be more accurate because of the lower powers involved. Similar to LASIK, enhancement requires good technique and experience.