It is generally accepted in laser eye surgery that a certain percentage of patients (varying with the type of correction) will be “undercorrected” or “overcorrected” or will “regress”. In many cases this is treated by doing additional laser surgery in attempt to reach the original target.

It is an unfortunate reality that in too many cases the “enhancement” concept is being used like the proverbial hammer in the hands of the man with no other tool: Didn't work? No problem – let's enhance you. This overlooks many factors which may make some patients better candidates for an enhancement than others. A patient's suitability really must be be re-evaluated from scratch, taking into account certain complex factors which were not even part of the picture before the original surgery.

How can YOU be sure an enhancement is right for YOU?

We have prepared several questions for you to consider, which we hope will give you a better understanding of what is involved in an enhancement and what information you and your doctor need before proceeding.
 

1. What IS an enhancement?

First, let's get our terminology straight. “Enhancement” (or worse, “touch-up”) is a naming convention developed by marketers to make the idea of additional surgery more palatable to people like you. Period. Judging from the numbers of people who get it done, it's very effective. (Can you think of any other form of medical surgery where they can do a surgery to fix what they got wrong the first time, and call it an enhancement?)

The proper term is “retreatment.”

So what is a retreatment? A retreatment is any additional laser surgery (LASIK, LASEK, PRK etc.) that you undergo on an eye that has already had one or more such surgeries. Note that retreatments fall into two categories: conventional (using what is called a standard nomogram), or wavefront (sometimes called complex wavefront retreatment, which uses data from a scan of your eye to program the laser with). Here we will discuss only conventional retreatment. In a retreatment context, wavefront is a different animal altogether.

How is it done? It depends on the type of surgery.

In a LASIK enhancement, there are two possibilities. 1) They can re-lift the flap that was cut during the original surgery, and then fire the laser at the tissue underneath; or 2) they can cut a new flap (which may be within the original one – i.e. thinner and smaller – or may be larger and deeper than the original). Then they laser the tissue underneath. Normally, lifting the flap is preferable.

In a PRK or LASEK treatment, they do exactly what they did the first time around: remove the epithelium (“skin” of the cornea), and fire the laser at the tissue underneath.

Why get a retreatment? For the exact same reason as the original surgery: to eliminate or reduce refractive error – that is, the visual defects that make you need glasses. Which leads us to our next question:
 

2. Do glasses (or soft contacts) correct your vision?

If not, an enhancement is not for you.

It's as simple as that.

Why? Glasses compensate for refractive error (myopia, hyperopia, astigmatism). Laser surgery tries to replicate what your glasses do. If glasses don't fix it, neither can an enhancement. (Gulp.)

This is probably where the most mistakes are made in enhancement-land. Patients are understandably disappointed and distressed at getting “almost” there but not quite. They are reassured all they need is a little enhancement. They get it. It doesn't work. Why? In some cases, simply because the cause of their poor vision was NOT refractive error, so it was basically guaranteed to fail.

Don't let this happen to you. Get a full eye examination. While they are doing the refraction (you know, the better 1, better 2? type of test), pay close attention when they find the lenses that provide you with the best vision. That “best” vision with those lenses is pretty much the very best that you can expect with an enhancement, in a perfect scenario. If you do not see as well as you think you should see even through those lenses, you need to ask your eye doctor why. You may want to seek a second opinion.
 

3. Can you spare the tissue?

Most of you will have learned while preparing for your original surgery that the thickness of your cornea is a key factor in the safety of the procedure. (If you've forgotten, see our previous editorial, LASIK Hot buttons, and look at #3 – Corneal thickness.)   If you have had LASIK, it is the tissue remaining under the flap that holds the cornea together after surgery, not the flap (which just sort of sits on top) so it is only the thickness of that under-part, called the stroma, with which we are concerned.

So how much “stroma” have you got? - You may be surprised to know just how difficult it is to get an accurate answer to that question. In fact, without sophisticated diagnostic equipment that the vast majority of optometrists and ophthalmologists do not possess, it is not possible to determine how much stroma you have. When you ask your doctor what your “residual stromal thickness” (RST) is and he says 310, he doesn't know that for a fact. He is assuming that (a) the microkeratome cut the flap exactly the thickness it was programmed to do, and (b) the laser removed just as much tissue as it was programmed to, and he is subtracting those numbers from your original total corneal thickness.

But, you say, that sounds perfectly reasonable! Sure does. That's why so many people rely on it, including most doctors. The only problem is that it's not borne out by the medical literature, which demonstrate amply how poor a track record many popular microkeratomes have in terms of achieving the programmed thickness flap, as opposed to something up to 20% thicker or thinner.

But, more to the point, do you have enough to spare some for more surgery? And just how much IS enough? That is open to debate. The industry “standard” is probably 250µm. Some are comfortable going lower than that. Some say you need at least 280 to be safe. Some say 300. What IS safe? With corneal ectasia – a progressive condition caused by corneal thinning and which if you get it basically means you will eventually need a transplant – on the rise in a big way, this question is directly relevant to the future health of your eyes.

Our recommendations for patients seeking enhancement are that they (a) either get an examination (such as with Artemis) which will accurately determine their RST, or simply assume the flap is 20% thicker than it is to be on the safe side; and (b) always apply the most conservative standard as regards the minimum tissue to be left after the enhancement.
 

4. Do you have a high enough prescription?

Sounds counter-intuitive, doesn't it? After all, it's the fact that it's just a little bit of prescription that makes it qualify as an “enhancement”, right?

Well, the fact is that excimer laser technology is not quite as precise as you may be thinking it is, for a variety of reasons (some biomechanical). That's why there are overcorrections and undercorrections in the first place. These surgeries tend to be accurate to within a dioptre. That means that if you have a residual prescription of -0.50 or -0.75, well, an enhancement just doesn't make sense. If you have a little bit more than that, say 1 to 1.5 dioptres, you need to think very carefully about whether trying for an improvement is worth the risks you will undergo (see Question 6 below).
 

5. Why didn't it work the first time?

Sound silly?

But it's a valid question.

Logically, there are only so many possible explanations for a result that is way off. Either the laser was programmed wrong by the doctor, which is very unlikely, or the laser failed to deliver the correct amount of energy, which is more than a little scary, or... what?

Whether there is another explanation depends on whether you are under- or over-corrected. In an overcorrection, too much tissue is removed. Period. Don't let anyone talk you down with this “your corneas over-responded” baloney if you are seriously overcorrected. Trust me, the molecules in your cornea don't spontaneously combust. If tissue is ablated, it's because the laser did it. A small overcorrection can be explained away without too much trouble as variances in laser fluence or whatever (but then, you don't want to enhance a small overcorrection anyway, for the reasons explained in Question #4). But a large overcorrection is a bit worrying.

Then let's consider undercorrection and regression. Again, it could be the laser.   But then there's also the biomechanical response of the cornea to be considered. Now, what you have to understand about laser surgery is that it assumes your cornea is going to behave a specific way. It assumes that not because it knows that about you personally, but because it has added up how a lot of other people's corneas behaved and then averaged them (more or less).

What? You mean you don't have an industry average cornea? Sorry. You're out of luck, and you're one of X% who are undercorrected or who regressed. Better luck next time.

But what WILL happen next time? I mean, if your cornea has not responded according to the predictions and assumptions made by the technology itself, what makes you think it will the next time around?

Dear oh dear, where are we going with this? At this rate, one would think all enhancements are doomed to failure. Are they? No, of course not. Many are successful. And you may be – so long as you consider all our other questions, set realistic expectations, and are willing to spin the bottle again. Which leads us to our next question:
 

6. Are you motivated enough to incur more risk this time than the first time?

“What do you mean MORE? This is just a touch-up, for Gawd's sake!”

Right?

Wrong.

In LASIK, and assuming the flap will be lifted rather than re-cut, certain complications are thankfully eliminated altogether (specifically, all those which are associated with the microkeratome, the tool used to cut a flap). However, wouldn't you know it, other complications increase to make up for it. One of the worst offenders is epithelial ingrowth, where cells from the epithelial “skin” of the cornea congregate underneath the flap. It's a nasty one, especially if it grows unmonitored. To treat it they have to lift the flap and scrape out the cells. If left untreated, it can cause the flap to “melt”. You don't want that to happen. Trust me.

I recently attended a major industry meeting in Paris. During an instructive course on complications, a prominent American surgeon stated that “Flap lift enhancements have three times the complications rate of primary treatments, if we're honest about it.” I would certainly expect a surgeon to be honest with him/herself, and with me too, when it's my eyes that are at stake.

“Three times” as many may still be a reasonably small number. But you have the right to know that complications are an issue, even in “enhancements”. Informed consent applies to each individual surgery – there is no blanket informed consent which covers additional surgeries. The moment you got the first surgery, everything changed.
 

7. Have you waited long enough?

Which begs the question, how long IS long enough?

As long as it takes for your vision to stabilise. For one person this may be weeks, for another months or even a year or two.

It is generally accepted in laser surgery that it is safe to perform an enhancement three months after the original surgery. That, however, does not mean that it is in your best interests to perform an enhancement three months after the original surgery.

We worry that many patients undergo an enhancement prematurely and largely for reasons of convenience – whether their own, or their clinic's or both. We humbly remind all patients that every surgery removes more tissue which will never grow back. You were blessed with only so much cornea. Once gone, it's gone for good. You cannot keep “enhancing” your eyes forever. If you get an enhancement at 3 months or 6 months and continue to regress, you may find yourself wanting another at 12 months or 15 months. How many surgeries do you think you can have without permanently compromising your vision?

Just get some glasses and wait another six months. Sure, it's not what you envisioned when you went in for surgery. But consider what is at stake. Your vision is too precious to compromise by premature surgery.