All you wanted to know: LASIK FAQs

1. What is LASIK?

LASIK is an operation on the front of the eye, the cornea, to correct spectacle power like shortsightedness and astigmatism.

During this surgery, a thin layer of the cornea (the flap) is partly separated and then an excimer laser is used to reshape the front surface of the eye (the cornea). The flap is then replaced in its original position on the eye.

LASIK Part 1: Creating the LASIK flap with a femtosecond laser

LASIK Part 2: Lifting the flap and performing corneal reshaping with the excimer laser

2. Why go for LASIK?

Glasses and contact lenses actually work very well. But, they sometimes get in the wearer's way. Hmm, going swimming? Better get those contact lenses out first, or gingerly get into the pool and make sure the goggles are fitting well with no leaks.

Fogging of glasses can be annoying...

Spectacles can fog up when going from a colder to a warmer place, or when having a hot drink/meal. Plus, the field of view is limited to the spectacle frame, and strong spectacle lenses can cause distortions at the edge of the lenses. That is why a lot of people with high spectacle powers prefer contact lenses.

Having LASIK done is somewhat like having contact lenses built into the eye, so that one does not have to worry about the daily routine of lens wear, the cost of the lenses, or the dryness and allergies that lenses can cause.

For many patients, the best things after LASIK are waking up in the morning to immediate clear vision on opening the eyes, or going to sleep without having to bother about taking out the contact lenses!

3. What is wavefront LASIK?

Although our corneas and eyes look round and smooth, in fact there are little irregularities that cause us to see starbursts around stars. We call these irregularities aberrations.

Wavefront guided LASIK aims to reduce or correct these aberrations ie to improve the focusing of the eye. The benefits of wavefront guided LASIK are more obvious

1. In people whose eyes already have more aberrations before LASIK
2. When seeing things in the dark/at night after LASIK surgery

Some clinics use the term 'wavefront' loosely, to include wavefront optimized treatments and so on. In fact, wavefront optimized is a kind of standard LASIK that does not take a person's own corneal irregularities into account.

True customized treatments are either (ocular) wavefront guided or corneal wavefront/topography guided. Do clarify with your doctor whether your treatment is 'wavefront optimized' or 'wavefront guided', as the former is a kind of standard treatment and the latter is true customised treatment.

To be fair, not everybody needs wavefront guided treatments. People who are lucky enough to be born with few ocular/corneal aberrations would do just fine with wavefront optimized treatments. Also, wavefront guided treatments usually take more corneal tissue, so sometimes for people with thinner corneas, wavefront optimized treatments may also be more appropriate.

4. What is the difference between epiLASIK and LASIK?

epiLASIK involves surgery that uses a special blade to peel the surface layer of cells off the cornea, then the corneal surface is treated with the laser. In epiLASIK, no corneal flap is made. In LASIK, a corneal flap is made with a special laser called the femtosecond laser.

With epiLASIK, only the layer of epithelial cells is scraped off before laser reshaping. As the cells die and are thrown away, the patient has to wait for them to slowly grow back. 

With LASIK, there is a thicker corneal flap that is replaced at the end of surgery. Repositioning the flap means that there is immediately a healthy layer of cells at the end of surgery, so recovery is much faster than epiLASIK or PRK.

Disadvantages of epiLASIK:

1. Without a flap, epiLASIK patients take much longer to recover than LASIK patients as they have to wait for the surface cells to grow over the cornea. The recovery is like PRK, and vision may take several months to get to its clearest level. In comparison, for LASIK vision is very good the next day and often reaches its best level within 2-3 weeks.
2. Also, with epiLASIK there is a risk that the blade may cut deeper than it is supposed to, resulting in an uneven cornea and permanent blurry vision.

That is why I do not perform epiLASIK. If a patient engages in rough contact sports and prefers not to have a LASIK flap, then I would recommend alcohol-assisted PRK (LASEK) or Transepithelial PRK (TPRK).

5. How do I take care of my eyes after LASIK?

Immediately after LASIK, the eyes may feel mildly irritated and vision is misty.

Remember to put the eyedrops prescribed and use a shield to protect the eyes while sleeping. Sunglasses are useful when going outdoors.

One must not rub the eye at all, and avoid splashing water into the eyes. Swimming is to be avoided in the first month. Other sporting activities can be commenced earlier, for example, going to the gym should be fine after 2 weeks.

6. Is it true that the eye never heals after LASIK?

Although the corneal flap does not stick down and heal to 100% of its original strength, it does heal and after 1 month the flap does not shift even if the eye is accidentally rubbed. In fact the flap is extremely stable after the normal recovery period.

The safety of LASIK is attested to in many ways, for example, athletes like Lebron James in the NBA had LASIK done, and NASA allows people who have had PRK or LASIK to become astronauts:
http://astronauts.nasa.gov/content/faq.htm

There is actually an advantage in this feature of LASIK. If at any point some spectacle power creeps back, the LASIK flap can be lifted, and a minor adjustment/enhancement procedure performed. This can be done provided that the underlying cornea is thick enough.

7. What are the upper limits of spectacle power that LASIK can treat?

Depending on the thickness and original curvature of the cornea,

• the maximum shortsightedness that can be treated is about -11 to -12D (1100 to 1200 degrees), 
• astigmatism -5D (500 degrees), and 
• longsightedness about +5D (500 degrees). 

In exceptional cases, higher powers have been treated, but the risks are of a small optical zone causing halos and other visual disturbances, or of regression ie some of the spectacle power comes back.

8. (Update) Is there a lower limit of spectacle power that LASIK treats?

Generally speaking, the lowest spectacle power that I treat with LASIK is in the region of +/-0.50D. With a lower power than that, most patients are not that bothered by the slight blurring of vision.

In special situations, I may treat lesser spectacle powers than that. This applies to patients with irregular corneas, such as after prior refractive surgery or corneal scars, where the measured spectacle power may be low but the visual quality is poor due to what are called 'higher order aberrations'. These patients need special topography guided LASIK/PRK.

9. Who is suitable to have LASIK?

1. People who are between the ages of 20 and 60 are candidates for LASIK if the spectacle power has been stable (no change of 0.5D/50 degrees or more) for a year or more.

2. Younger ladies who are pregnant or breast feeding should wait until the baby is delivered, or until they stop breastfeeding before having LASIK as the hormonal changes may affect their spectacle power and the long term accuracy of the LASIK correction.

3. Patients going for LASIK should not have other eye conditions such as cataracts or glaucoma.

Above 60 years of age, the issue is the possibility of cataract developing in the next few years after LASIK. Cataract surgery is another way to correct their spectacle power, so the effect of the LASIK procedure may have been only for a few years. Occasionally I do perform LASIK for these patients, but only if the lenses in their eyes look very clear on examination.

With glaucoma, the issue is that LASIK thins the cornea, and this can affect the measurement of the pressure of the eye, which is important in glaucoma. After LASIK, the measurements may show a lower pressure than the actual pressure in the eye, however, as long as the eye doctor is aware that prior LASIK has been done, he can make suitable adjustments and the glaucoma can still be treated.

10. What are the side effects of LASIK?

After LASIK, most eyes become temporarily drier during the healing process. This is helped greatly with artificial tear drops and sometimes with plugging of the draining tear channels. Usually the dryness goes away as the eye heals. By 3 months, about 90% of eyes are no longer dry, and by 6 months >95% of eyes are back to normal.

Halos are common in the early period after LASIK. This is due to slight roughness of the corneal surface (and interface) as it heals. Most of this early halo effect will disappear within a month after surgery. Some halos persist after one month, and these are commonly due to other problems, such as an optical zone that is too small, decentered optical zone, or other aberrations and irregularities. If these are persistent, corneal mapping (topography) should be done to see if specialized topography guided treatment might help.

11. Can LASIK treat presbyopia (Lao Hua)?

LASIK cannot actually treat presbyopia. However, there is the option of 'monovision', which means one eye is fully corrected to see distance clearly, while the other eye is made slightly shortsighted so that it can see clearly at near.

Having 2 eyes with slightly different spectacle powers is something most people get used to, and they do not need glasses for most things. Occasionally they may wear distance glasses for certain activities such as driving at night or reading glasses for really close up viewing.

There are some laser centers and machines that offer 'PresbyLASIK'. There are many other names for this kind of treatment such as PresbyMax or SupraCor. This works by trying to give the cornea a multifocal shape. However, most doctors prefer monovision compared with PresbyLASIK, because

1. The multifocal shape can cause poorer distance vision and side effects such as increased halos
2. The multifocal shape often does not last due to the healing process of the cornea
3. The effect is often modest and many patients still need to wear reading glasses in the end

12. Do LASIK doctors go and have LASIK done themselves?

Doctors (including eye doctors) are just like any other group of people). Some of them wear glasses, others wear contact lenses, and some of them have also had LASIK done. One well known LASIK surgeon who had LASIK done himself is Dr Arthur Cummings, and you can read his account of it here.

http://bmctoday.net/crstodayeurope/2014/02/article.asp?f=why-i-chose-to-have-lasik

13. What is the best age for LASIK?

Please see my previous blog post here.

14. Why did the Taiwanese doctor stop doing LASIK?

In February 2012, Dr Ray Tsai announced that he would stop doing LASIK, because some patients developed poor vision many years after their surgery. While the exact problem was not mentioned, he was probably referring to a problem called 'ectasia'. In the past, doctors were not as aware about the signs of corneal weakness, and with older equipment there was a higher chance of making the cornea too weak. In some patients whose corneas became too weak, the normal pressure in the eye caused the weak cornea to bulge outwards. This causes distorted vision and irregular astigmatism.

A large study conducted by SNEC found that the problem in Singapore was rare, occurring in about 8 out of 30000 cases. The risk is probably even lower nowadays, because:

1. Doctors are more aware of the features that are shown by a weak cornea, and these cases rightly are told they are not suitable and do not get LASIK

2. With newer machines like the femtosecond laser to create LASIK flaps of very precise thickness, the risk of corneas getting too thin is minimized

3. There is now 'LASIK Xtra', a way to strengthen the cornea with vitamin B2 and ultraviolet light at the end of LASIK. LASIK Xtra may also reduce the risk of regression (power coming back) in patients with high spectacle power or those with longsightedness

Even if a patient develops ectasia, the process can be halted or stabilized with cross linking treatment, which is like LASIK Xtra but takes a slightly longer time. The important thing is to catch it early. Therefore, if any patient notices that his/her vision is getting blurry after their LASIK, they should get their eyes checked again by their doctor soon.

EpiLASIK, ICL or LASIK?

In recent years, LASIK has become one of the commonest operations performed. Its popularity and success are understandable, given the good outcomes experienced by the majority of patients. Still, there are potential side effects with any procedure, and LASIK also has its limitations especially for those with very high spectacle degrees. 2 commonly mentioned alternatives are epiLASIK and ICL (implantable collamer lens), and in Singapore these 2 procedures have been marketed quite heavily as well. Some of their proponents would have you consider undergoing these ops rather than LASIK, and in their reading material sometimes emphasise the potential side effects of LASIK. So, what's the deal with these alternatives and are they really to be preferred over LASIK?

There are pros and cons with each procedure. With epiLASIK, the advantage (which is also a disadvantage, as you will see later) is that no corneal flap is created, so theoretically the eye is stronger and perhaps at somewhat lower risk for a complication called corneal ectasia.

Having said that, the vast majority of cases that we do are LASIK rather than epiLASIK. Visual recovery following LASIK is much faster than after epiLASIK. In comparison, vision the second day after LASIK is already pretty good (usually in the region of 6/6 and 6/7.5), but for epiLASIK, to reach a comparable level of vision you might need to wait several weeks. We also take precautions not to go below 250 microns of residual stromal thickness and this avoids ectasia in normal LASIK patients (the risk being in the region of 1 in 5000 cases or so).

The problem with epiLASIK/LASEK/PRK procedures is that the corneal epithelium is removed (see below). Healing of this to provide a smooth surface will take from several weeks up to a couple of months or so. Because the surface is ablated, there is a chance of corneal scarring, but this is much less nowadays since we use mitomycin C at the end of epiLASIK/LASEK/PRK. 

I have grouped epiLASIK/LASEK/PRK together since they are essentially the same procedure. The difference is in how the epithelium is removed. In epiLASIK, a special blunt blade (tissue separator/microkeratome) cleaves the epithelium from the stroma. There is a risk that the blade may cut into the corneal stroma sometimes, resulting in an uneven surface, and because of this risk we don't do epiLASIK in our clinic. LASEK uses alcohol to loosen the epithelium, and this is our method of choice if we decide on surface treatment for a particular patient. The LASEK we do is 'epithelium-off', or 'alcohol assisted PRK' (see below in italics). Traditional PRK used a toothbrush type scrubber and we think the alcohol is gentler to the eye. In our clinic we currently reserve LASEK for patients with corneas that are too thin for conventional LASIK. The number of patients who have this done is probably less than 5%. The others all have LASIK with a 'bladeless' technique ie. using a femtosecond laser to create the flap and then the excimer laser to reshape the cornea.

A little bit of history: Why, might you ask, did people invent different ways to remove the epithelium when it could very easily be rubbed off with any instrument at hand? Well, it turns out that once people realised how long an eye took to recover from PRK, they tried to keep the thin epithelial cell layer intact and replace it at the end of the operation rather than throwing it away. The 2 ways of separating the epithelium while keeping it intact were 1) using alcohol to loosen the epithelium (LASEK) and 2) using a special blunt blade (epiLASIK). It turns out that once the epithelium is peeled away, whether by alcohol or the blunt blade, it dies. If this dead layer of cells is replaced, it slows healing down even more! Therefore, nowadays, usually even when LASEK or epiLASIK is done the epithelium is thrown away rather than replaced. So that makes it identical to PRK, doesn't it? Why spend money on an epiLASIK blunt blade when you can simply peel away the epithelium, perhaps with alcohol to loosen it first? There just doesn't seem to be a role for epiLASIK...and furthermore when you use a blade, even a blunt one, you run the risk of cutting into the stroma when you don't want to...

The ICL (above) is similarly different, with different pros and cons. When LASIK is done for patients with very high spectacle degrees or thin corneas, the area of cornea treated (optical zone) is smaller, so that the cornea does not get too thin. Unfortunately, when the area treated is small, the risk of halos in the dark and poorer quality vision also rises. The good thing about the ICL is that halos, even if present, are usually very mild even when the spectacle power corrected is high. It is also true that after ICL, the eye does not get as dry as after LASIK.

However, potential intraocular (inside the eye) complications exist with the ICL, of which cataracts and glaucoma are the 2 main (but rare) ones. The main thing about reducing complications with the ICL is to achieve accurate sizing, and at our clinic we do 'sulcus to sulcus' measurements for all ICL patients. What is the sulcus? This is the little nook in the eye just behind the iris (coloured part of the eye) and in front of the original crystalline lens where the ICL will sit. If the ICL is too big for this space in a particular eye, it will be 'squashed', bend forwards, and narrow the drainage angle of the eye (increasing the risk of glaucoma). If the ICL is too small for this space, it will sink backwards and touch the crystalline lens, thus causing a cataract. Although there is no perfect way to measure this sulcus diameter down to the last micron, we have found the Artemis VHF ultrasound biomicroscope (above) to be very accurate and allows us to choose an appropriate size ICL. The figure below shows a measurement made by the Artemis.

I would say that for my patients with lower spectacle powers, LASIK provides excellent clarity of vision including night vision (and without the risk of any intraocular complications). I have performed ICL surgery for a number of patients with excellent results, but I think bearing in mind the potential seriousness of problems with the ICL my preference is still an extraocular (outside the eye)  procedure like LASIK in cases where I judge that the outcome will be good. Extraocular means zero chance of causing cataract or glaucoma. Actually, I think the ICL is wonderful, but I prefer to use it for patients with very high powers or thin corneas, where I feel that the risks of intraocular problems are outweighed by the better visual quality that can be obtained with the ICL in such cases compared with LASIK. Although a lens is implanted into the eye in both ICL as well as cataract surgery, an ICL op is quite different from a cataract op, not least because when an ICL is implanted the patient's original crystalline lens/cataract is left alone while during a cataract op the crystalline lens/cataract is removed and is replaced by an intraocular lens implant (IOL). This has implications because there are some doctors out there who perform 'clear lens extractions' to correct high spectacle degrees. If a 'clear lens extraction' (which is like a cataract operation) is done in a younger person less than 45 years old or so, then they will immediately lose the ability to focus for near ie develop immediately the maximum amount of presbyopia/LaoHua. ICL surgery will not affect the development of presbyopia, nor can it cure this problem. ICL surgeons can offer monovision with the ICL, just like with LASIK or contact lenses. On the other hand, if somebody has a cataract then he/she should have a cataract op, not an ICL op. The ICL surgery doesn't do anything about a cataract, which would continue to blur the vision.  Overall I would say, go for LASIK if your cornea is thick enough because the theoretical advantages of epiLASIK probably do not bear out clinically for the majority of patients. ICL surgery is a great option for those who would otherwise be at risk for visual or other side effects from LASIK.