Laser Vision Correction
Refractive error is when the light from an object you are looking at does not focus accurately on the retina. There are 4 types of refractive error and you can have more than 1 type at the same time.
Short sightedness (myopia) is when the light rays focus too close, which means near objects are seen clearly but distance are not.
Far sightedness (hyperopia) means the light rays focus too far back, meaning distance vision is better than close, and with age distance vision becomes difficult as well.
Astigmatism means the eye has 2 focal points because the cornea is shaped liked a rugby ball instead of a soccer ball. This means vision is not clear at any distance.
Presbyopia is progressive hardening of the eye’s internal focusing lens which usually occurs in our mid to late 40s. It will affect everyone sooner or later, and results in the need for reading glasses in people who have normal distance vision.
While many people may be happy to wear glasses or contact lenses there are also plenty who are not. Modern refractive surgery is able to correct most refractive errors to allow high quality vision without glasses, but the best sort of procedure depends on numerous factors, including the refractive error, the anatomy of your eye, your age and the presence of any other medical conditions.
Laser Assisted In Situ Keratomileusis (LASIK) is the most popular refractive procedure in Australia. A paper thin flap is created on the front of the cornea (the glassy window at the front of your eye) and then an excimer laser is used to precisely and safely change the shape of your cornea in a matter of seconds. For myopic corrections the cornea is flattened and for hyperopic corrections it is steepened. The flap is then repositioned allowing minimal pain and extremely rapid visual recovery. Most people can begin to see within minutes of the procedure and almost everyone can drive the next day.
Originally the flap was created with a microkeratome, a precise oscillating blade, which passed across the cornea. For the last 10 years the preferred technique has been to create the flap with a femtosecond laser as this is significantly safer and results in better visual outcomes.
LASIK is able to treat a very wide range of refractive error, from +6 to -12 and 6 diopters of astigmatism.
LASIK treatments are usually painless and take approximately 5 minutes per eye to complete. Most people will achieve high quality vision by the morning following treatment. The most common downside is dry eyes, which is usually temporary and the occasional need for re-treatments, or enhancement which is needed in 3% of cases. Vigorous exercise should be avoided for 4-5 days and no contact sports should be played for 4 weeks, but by 4 weeks the flap is rock solid strong and there are no long term restrictions in activities.
Photorefractive Keratectomy (PRK) is when the same excimer laser used in LASIK is directed to the front surface of the cornea once the transparent skin (epithelium) has been removed. Epi-LASIK and LASEK are variations of PRK which are not widely used any more.
The advantage of PRK over LASIK is excellent strength of the cornea straight away. This is particularly useful for highly active people and those involved in contact sports or jobs with high risk of trauma (military, police etc). PRK is usually cheaper than LASIK as only 1 laser is required instead of 2.
The downside to PRK is slower visual recovery. Most people won’t be able to drive for 4-5 days, and while vision is quite good after 1 week it may be as long as 2-3 months until final sharpness is achieved. PRK is also best for relatively low scripts, up to about -3.0 myopia with low astigmatism. It is generally not recommended for hyperopic or high myopic/astigmatic corrections.
The latest laser vision correction technique is Small Incision Lenticule Extraction (SMILE). This uses the same femtosecond laser used to create modern LASIK flaps to complete the whole treatment internally with only a 2mm keyhole incision, instead of the near circumferential incision of a LASIK flap. This allows virtually instant near normal strength, so there is no restrictions in activities following a SMILE treatment. Because the corneal surface is less disrupted there is also a lower incidence of long term dry eyes than LASIK or PRK, but it can still occur.
The downside to SMILE is that the laser interface is more complicated, so it is a more expensive treatment. It may also be more difficult to perform an enhancement if required, though it is still possible. Vision may be slightly slower to return to normal than with LASIK, but much faster than PRK. More corneal thickness is needed for a SMILE treatment than LASIK or PRK, and it does not work as well for very low or high shortsightedness and it is unable to correct hyperopia.
The final visual outcomes for all these laser treatments is essentially the same, and the safety profiles are similar and excellent for all of them as well. The choice of best treatment depends on personal preference, desired speed of return to physical activities and individual factors such as corneal thickness and correction required.
Not everyone is suitable for laser correction, usually due to degree of refractive error, age or individual corneal variations. There are excellent alternative treatments available for many people who are unable to have laser vision correction.
Phakic Lens Implant
For young people whose refractive error is too high or whose corneas are too weak for a laser correction a phakic lens is usually the preferred option. There are several varieties available, but for most people an Implantable Collamer Lens (ICL) is the best. As long as you are under 45 years of age and you have adequate anterior chamber depth an ICL has an excellent chance of giving you a great result. The best thing about ICLs is that they give high quality vision no matter how bad your refractive error. They are not dependent on corneal thickness, are reversible and have less effect on dry eyes. The downside is that they are relatively expensive and there is a risk of significant complications such as cataract and glaucoma which you do not get with laser correction. These risks are very low, but because the surgery is inside your eye there are more things that can go wrong than with laser which is on the outside of your eye. If you have a high prescription, tin corneas or significant dry eyes though the results are usually amazing, and the fact the procedure is reversible is comforting to many people.
For hyperopes over the age of 45-50 and myopes over the age of 55 a laser correction can be very effective but is usually temporary. It is possible for the improvement in vision to last as short a time as 2-5 years before glasses or another surgery is needed. For this reason a lens replacement surgery is generally preferred. This is called a cataract surgery if you have cataracts and a clear lens extraction if you do not. This involves removing the natural lens of your eye and replacing it with a plastic lens which also corrects for your glasses. The main benefit of this is that the result is permanent. There are multiple lens options available (see here for a discussion of intaocular lens choices) and the usual result is a permanent improvement in vision, no risk of developing cataracts in later life and the option of multifocal lenses which means no distance or reading glasses should be needed. The downside is that this is a more invasive irreversible procedure. Complications are rare but potentially serious. Once done though most people will have permanently improved vision that they do not need to worry about as they get older and most people should never need glasses ever again.