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.

The best age to have LASIK

So, young, middle, or old? What's the best age?

Is there a best age to have LASIK? I get asked this question quite often when patients enquire about this surgery and the short answer is yes, with some caveats.

I suppose when we decide to have something done (eg surgery), or even when we buy something, we want to get the best that we can get for what we pay. In other words, value. Even more importantly for surgery of course, we want to get a good outcome, and we want to ensure quality and safety, but value is a common factor that pervades many aspects of our lives.

LASIK is somewhat different from other types of surgery, because what you get out of it is influenced by the age when it is done. Let's take a few scenarios.

A typical patient in their 20s comes for LASIK. In such a situation, both eyes are corrected for distance, so everything is clear after surgery, whether it is something far away or something close up that is being looked at. However, when this patient gets to his/her early forties, they are just like any other patient who does not wear glasses for distance, ie near vision for reading slowly starts to get blurry, and they find they have to start holding things further away. This condition is called presbyopia. At some point, reading glasses are needed for comfortable close work like reading.

When a patient comes for LASIK and they are already in their forties or older, presbyopia is an issue that needs to be considered straight off, at the time of the pre-LASIK consultation. This is because LASIK cannot 'cure' presbyopia as such. The usual option offered to patients who desire spectacle independence is monovision, with its attendant compromises. PresbyLASIK is unfortunately unpredictable in its effects, and so far corneal inlays have also shown problems relatively commonly.

Having said this, many presbyopes are very happy with monovision LASIK. The important thing is to allow a trial period of monovison adaptation to see if patients can tolerate it. This simulation is best done with contact lenses. If a patient does not tolerate monovision with contact lenses, then if LASIK is done both eyes should be corrected for distance and then reading glasses worn for near. Therefore it can be seen that LASIK after the age of 40 or so does not provide as much clarity of vision for all distances compared with when it is done earlier, and also involves some compromises, whether it be monovision or reading glasses for near work.

The next group of patients to consider are those 60 and above. Generally speaking, age is associated with an increased incidence of cataracts, especially with those above 60 years of age. The issue with cataract development is that once a patient has cataracts, then they are no longer suitable for LASIK, since the cataract will blur vision even if LASIK is performed. Furthermore, doing cataract surgery is also a way to correct spectacle power, giving an effect like LASIK. In some ways, you could consider cataract surgery as having the ability to reset the power of the eye, therefore, this is the point where the effects of the LASIK surgery are 'lost'.

To cut a long story short, the best age to have LASIK in my opinion is the early twenties, once spectacle power has stabilized and remains unchanged for more than a year. Patients above 40 will still benefit from LASIK, but one might want to consider certain compromises to avoid reading glasses. Generally, patients above 40 who do get LASIK done avoid progressive/bifocal spectacles, which many people find difficult to get used to. Glasses, if needed, tend to be reading glasses, or occasionally distance glasses for monovision patients who drive a lot at night.

Can spectacle power return after LASIK?

LASIK changes the power of the eye by changing the shape of the cornea, the clear window at the front of the eye. Besides transmitting light, this window is also responsible for much of the focusing power of the eye, giving doctors a great opportunity to 'build a contact lens' into the eye itself.

LASIK works by removing minute amounts of corneal tissue from the surface of the eye. By doing so, certain parts of the cornea can be flattened, and other parts steepened. For example, in shortsighted patients the central part of the cornea is flattened, the amount of flattening corresponding to the spectacle power of the patient.

Back to the question: Can spectacle power return after LASIK? The short answer is yes. This can happen for a few reasons:
1. The corneal shape slowly regresses towards its original shape (It can never regain its original shape, but the 'healing' process sometimes causes the corneal curvature to become a little more like how it was before the LASIK)
2. The eyeball changes in length, usually by becoming longer in very shortsighted people
3. Some other unrelated eye disease, such as cataract

The higher the spectacle power of the eye to begin with, the more likely this is to happen. However, overall the risk is low as has been shown in a number of studies.

Am J Ophthalmol 2008;145:46–54. 

The above graph from an article in the American Journal of Ophthalmology shows that even after 10 years, the average spectacle power of the eyes of a group of patients was only about 50 degrees, or 0.50 dioptre of shortsightedness.

If the spectacle power returns, what next?

It depends on how much power has come back, how much cornea is left, and how keen the patient is on having a LASIK enhancement/adjustment.

Generally speaking, an enhancement is not recommended if the residual spectacle power is 50 degrees or less than targeted. Some patients are also quite happy if the power is higher than that, and there is no need to repeat surgery for all these patients.

When the power gets to 75 degrees or higher though, more and more people find that it affects their daily activities. They may need glasses, for example, when driving. If so, the inconvenience may drive them to seek an enhancement. This can be considered if the remaining cornea is thick enough.

In recent times it has been found that a LASIK flap can be lifted again many years after the original surgery. As such, an enhancement surgery is very much 'half an original LASIK operation', since it does not involve making another flap. Using topography guided techniques, enhancements can be done not only to correct residual short/long sightedness and astigmatism, but also aberrations like spherical aberration and coma. The picture below shows topographies (corneal maps) of a patient who had coma and residual shortsightedness before (left most map) and the subsequent healing after enhancement. Note how the blue area has shifted from the right side (left map), over to the centre (right map).

If the cornea under a LASIK flap is already too thin for further treatments, alternative techniques would include PRK on the flap, or even ICL surgery if the anterior chamber of the eye is deep enough.

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.

LASIK surgery-Spectacle freedom with precision laser treatments

Around the world, millions of people have undergone LASIK surgery. It is a very effective procedure, which uses a laser beam to reshape the transparent covering at the front of the eye called the cornea. LASIK was introduced in the late 1990s, and essentially involves creating a very thin ‘corneal flap’, and then using a special ‘excimer’ laser on the cornea under the flap.

The LASIK procedure

Although LASIK is a very successful procedure, many people are concerned about undergoing surgery. Some patients have reported problems such as difficulty seeing at night and dry eyes after surgery. There is the potential of leaving behind some of the spectacle power that was to be treated, and a very small risk of infection.

Before Surgery

Such issues are of foremost importance at Jerry Tan Eye Surgery. Prospective patients undergo a comprehensive assessment to check their spectacle power, corneal shape and general health of the eye. Spectacle power is checked both without and with special eyedrops which relax the muscles of the eye so that the reading is as accurate as possible. Once the assessment is complete, careful planning of the procedure is performed.

The LASIK Procedure

Surgery at Jerry Tan Eye Surgery is normally performed one eye at a time. This enhances safety because there is no chance of infection in both eyes at the same time, even though the risk of this happening is extremely small. Furthermore, it allows fine adjustment of the treatment for the second eye, for a more accurate result.

The traditional method of creating a corneal flap made use of a special blade called a ‘microkeratome’. However, the corneal flap that was created was sometimes uneven, resulting in less optimal outcomes. At our clinic, most cases now have their corneal flaps made by a special laser - the femtosecond laser. It creates a series of bubbles in a perfectly uniform plane in the cornea. This allows a flap to be lifted, much like how a stamp can be torn in a straight line. The resulting flap is much more even in thickness and diameter. Older femtosecond lasers worked very slowly, but the iFS laser at Jerry Tan Eye Surgery creates corneal flaps in 10-15 seconds, minimizing patient discomfort while ensuring better vision after surgery.



How a femtosecond laser creates a corneal flap

The iFS femtosecond laser





After a corneal flap is created and lifted, an excimer laser is used to reshape the cornea. Modern lasers work very fast, and the new Schwind Amaris laser at Jerry Tan Eye Surgery works at 750 times a second. This means that 100 degrees of short-sightedness is corrected in 1.5 seconds. The Amaris laser also tracks eye movements at 1050 times a second in 6 dimensions, ensuring very accurate placement of the laser treatment. For most patients, the actual surgery takes a surprisingly short time in comparison to the time spent on assessment and planning.

Our Results

LASIK results

 At Jerry Tan Eye Surgery our results show that for patients with between 100-700 degrees of shortsightedness, 89% achieved perfect vision (6/6) or better. 55% achieved better than perfect vision.  After LASIK, 84% achieved refraction within 25 degrees of 0, and 97% were within 50 degrees of the intended final power.

Customised PerfectShape® LASIK

In order to avoid night time glare and haloes after surgery, we have developed ‘PerfectShape®’ LASIK at Jerry Tan Eye Surgery. In most traditional ways of performing LASIK, the cornea becomes more curved at the sides after treatment, and this causes poor focusing of light in the dark, when the pupils of the eye become big. PerfectShape® LASIK preserves the natural corneal contour as much as possible while using special corneal maps to guide the laser to smooth out any unevenness of the corneal surface. With PerfectShape® LASIK, night vision was the same or better after LASIK in 90% of our patients, which is remarkable considering that only a few years ago standard LASIK was causing glare and halos in many patients. In fact, PerfectShape® LASIK can be used to reduce night vision problems in many patients who had their LASIK done with older lasers.

A common problem encountered by LASIK patients after surgery is dry eyes. This is related to a disturbance of the eye’s surface caused by surgery. While it normally improves over several months as the eye heals, it can cause blurred vision and eye irritation. In our practice, this problem is less serious because we temporarily plug one of the tear drainage channels. This helps preserve the patient’s own tears on the surface of the eye.

Patients who are older than 40 years of age and undergo LASIK will have good vision for things far away, but near vision is not as good. This is due to presbyopia or ‘old sight’ (rabun tua). This cannot be cured by LASIK. We believe that the best way to reduce the need for reading glasses is ‘monovision’, which means that the LASIK is performed so that some shortsightedness is purposely left behind in one eye. Although with monovision only one eye has clear vision for distance and the other eye has clear vision for near, when both eyes are open all distances are generally sharp.

In summary, LASIK as a method for correcting vision continues to be refined, leading to better outcomes and fewer side effects for patients. Femtosecond laser corneal flaps and customised excimer treatments with the latest excimer lasers bring us closer to the goal of giving perfect vision to all our patients. The future of refractive surgery will bring further innovations, however, they will have to be compared to the gold standard which is current LASIK surgery.

Improving visual quality after previous LASIK

About 2 months ago I saw a patient who had LASIK done in another clinic a few months previously. His vision when measured on the reading chart was actually very good-it was 6/6 without glasses in both eyes. However, he was very disturbed by his vision at night. He was unable to recognize faces when the surroundings got a little dark, and vision in such situations was just generally blurred. Before his LASIK, his power was only about 500 degrees short-sighted.

When we did his corneal maps (topography), it was obvious why he had such problems. The previously treated zone was small, and it was also slightly decentered upwards. Our aberrometer shows clearly his predicament. When his pupil is 3mm in diameter (in bright light), you can see the image of the 'E' is sharp. When his pupil enlarges to 6mm, all you see is a shapeless smudge.

Last week I performed topography guided enhancement LASIK for his left eye. A comparison of the pre and post-operative corneal topographies shows that the central blue/green area is now larger. Subjectively, his night vision is much improved and best of all, his daytime vision also improved to 6/4.8 without glasses.

This case highlights an important aspect of LASIK which is often overlooked, sometimes because of the limitations of technology at a particular clinic. And that is-the quality of vision, on top of the spectacle power issues. In this day and age, we aim not just for minimal spectacle power after LASIK, but also the best quality of vision in all situations. There are limitations, such as for those with very high powers, because there will be issues with corneal thickness. But customizing a 'perfect shape' cornea should be possible for all those with low to moderate degrees of shortsightedness and astigmatism, such as in this case.

Wavefront-guided and topography-guided customized LASIK: What do they mean and what's the big deal?

In recent years, the word 'customized' has become ubiquitous in LASIK treatments. If you're not doing customised treatments, if you're only doing standard treatments, you're out. But aren't all treatments customised, since they're customised according to the refractive error you have? Let me explain.

There are 2 things that so called customised treatments aim to control for, that so called standard treatments do not. One is ocular 'aberrations'. Most of us know that vision is affected by short or long sightedness, or astigmatism. But our vision is also affected by other irregularities of the cornea and lens, called aberrations. The chief ones which cause problems are 'coma' and 'spherical aberration'. When present in large degrees, they can cause glare and halos especially when the pupil is large at night. So these 'customised' treatments aim to treat the particular aberrations of the individual eye.

Now, when most people talk about 'wavefront-guided', they are talking about 'whole eye' wavefront. But whole eye wavefront is affected by a few different things. It is affected by pupil diameter, it is affected by the state of focus of the eye (accomodation), and it constantly changes as the eye ages, primarily due to changes in the shape of the lens. Furthermore, most measuring systems for whole eye wavefront only measure several hundred points at most through the pupil.

Topography-guided LASIK, or more precisely 'corneal wavefront guided' LASIK, is LASIK based only on measurements of the cornea.This is advantageous, because the cornea does not change as much in shape throughout life-definitely less so than the lens. It does not change in response to pupil shape, nor does it change in response  to accommodation. Topographers measure corneal shape right out to the periphery, and typically measure in excess of 20,000 points. In most cases, corneal aberrations account for a majority of whole eye aberrations. It would thus appear that topography or corneal wavefront guided LASIK is the way to go.

Customised treatments also take your corneal curvature into account when delivering the treatment. Why is this important? Well, imagine yourself standing in the sun at noon, at the equator. Your shadow would be tiny, directly under yourself. If you were standing in London in winter at noon, your shadow would be much longer, because the sun's rays are coming at an angle. In a similar way, the laser's rays strike the cornea at an angle at the periphery of the cornea. If a cornea is of relatively standard shape, that's not a problem, because the laser has been programmed to treat relatively 'standard' eyes. However, if your cornea is more curved than normal, ie steeper at the sides, then the laser would strike your corneal periphery at a larger angle than normal and work less effectively. You could end up with a smaller optical zone than expected. You could end up with lots of night glare and halos.

So, go for customized LASIK if you can. Better still, go for Topography Guided/Corneal Wavefront Guided LASIK for best visual quality.