Tuesday, September 10, 2013


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. 
EpiLASIK blade cleaves corneal epithelium from the stroma

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.
The Artemis ultrasound biomicroscope

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.

Thursday, September 5, 2013

Eye doctor trivia

In Ophthalmology, as in many other fields, "innovation" is always regarded as a golden word and there are countless doctors/researchers at any time looking for better ways to treat a given eye condition. True innovation requires a number of qualities on the part of the "innovator", and perhaps it's as good a time as any to re-visit the stories behind some of the greatest inventions of the twentieth century.

He came from a family of doctors and clergy, and once was a lapchild of Florence Nightingale.

His father was an ophthalmologist, and following a distinguished stint in medical school received the FRCS (Fellowship of the Royal College of Surgeons) at the tender age of 25. Even around this time, before formal training in eye surgery, he had begun discussing the possibility of replacing crystalline lenses after cataract surgery with his father and close associates.

In 1940, Flight Lieutenant Gordon Cleaver was returning from a sortie in his Spitfire. In his haste to get into the plane that morning, he had forgotten his flight goggles, so when a bullet smashed through the canopy of his fighter, bits of perspex plastic from the canopy were blown straight into his eyes. In the end, he underwent 18 operations on his eyes and face, many of which were performed by this doctor.

It used to be said (something to the effect of) 'Thou shalt not have a foreign body in the eye'. And yet, it was quite clear in this particular patient that some of the remaining plastic pieces in the eye were not causing any problems even years after the original injury.

So this young doctor spoke with some spectacle manufacturers and eventually a small perspex disc similar in shape to the original crystalline lens was produced. This was implanted into the eye of a patient on 29 November 1949. It wasn't long before he felt the full force of hostility (and some might say jealousy) from his peers. For several decades, the topic was not even given a section for presentation and discussion at conferences. By the 1970s, though, the unquestionable benefits of implants over thick aphakic glasses were apparent and with improving lens designs, better results were also being seen around the world.
The first intraocular lens implant

Today, it is the unusual patient who does not get a lens implant. The question has become 'why didn't this patient get an implant?' rather than the other way round. And of course, this was the story of Harold Ridley and the intraocular lens implant, which has revolutionised eye surgery in fundamental ways.

He was a bit of a maverick, but a persistent one at that.

Finding himself unable to get into medical school in the United States, he applied and got accepted into the University of Geneva Medical School in Switzerland, where for a time he was spending more time composing music than on his medical studies. But fortunately for all of us, graduate he did, and became heavily involved with research into better ways of doing cataract surgery.

In the mid 1960s, he was given US$299,000 to find a way to remove cataracts through a small incision (cut). Going through more than 40 different ways of doing so, including a meat grinder (!) type of device, he failed every single time and was close to despair. " I thought I might face defeat better if I looked better, and so I prepared," this doctor wrote in his 1985 autobiography Through My Eyes. "The haircut came first, then a shoeshine, and finally, the dentist." 

At the dentist's, he was very taken with the then also new method of removing calcified plaque with an ultrasonic cleaner. After many hundreds of modifications later, including refinements in technique from many other surgical experts, we now have almost one day visual rehabilitation, with many patients achieving better than 6/9 vision on the first day after surgery.

The first phacoemulsification machine

Of course, I'm talking here about Charles Kelman, the legendary inventor of phacoemulsification, which is the gold standard for cataract surgery nowadays.

A common thread that runs through these innovators seems to have been a long standing conviction that something was not quite right and could be done a whole lot better. Although it seems so obvious to us nowadays, it took long and winding roads before conviction was translated into innovation. But for serendipity, sometimes, nothing might have come of it.

It has been said (on Ming Thein's blog and perhaps others) that he who tries 99 times and fails is seen as a fool, while success on the 100th time is a sign of great persistence in the face of adversity. Perhaps the frustration and fear of failing just before success is as good a motivating force as any!

For all the success that we see sometimes, I think the respect we accord to these pioneers should include a great dose of not just awe for their genius and intellect, but also their willingness to risk everything (peer respect and sometimes even careers) and to persist in the face of great adversity. In fact, it seems like the greater the uproar created, the greater the invention! The ability to think laterally and to find uses for seemingly unconnected things is also priceless. And to this end, I have viewed the increased sub and sub-sub specialization of the medical specialties with some concern, since the narrower world view could discourage cross-discipline exchange of ideas and methods.

As always, it is the devil in the details, finding the right balance between craziness of an idea and potential for success, and decisions regarding the distribution of limited funds, that will determine the success or failure of future endeavours.