Kate asked:

Hi,

I’ve been to consults at two clinics, one that does PRK, and the other LASIK (with a blade). Both clinics offered a similar quote and both said I was an ideal candidate for the surgery (I’m a healthy 23 year old female with mild astigmatism and the same prescription of -1.5 in both eyes since I’ve had glasses (2001). The only thing a out of the norm is that my corneas are a little steep (46). Is there going to be a benefit to me choosing one surgery over the other?

Cheers, Kate

Omar asked:

Good Afternoon Mr Allamby,
I’m considering getting some treatment on my eyes, but am very worried about the long-term effect cutting the cornea can have. As i get older and my eyesight deterioates. will the my eyesight be worse off than if i had just kept wearing glasses?

Omar, I think this is one of the most common worries that prospective candidates have when considering laser eye surgery be it LASIK or PRK. It is just over 20 years since we first performed PRK for short-sight, and just under 20 years for LASIK, so we have considerable experience of long-term results.

The long-term outcomes have been excellent to date. Regression is seen in the London PRK study in 1-2% of patients, with a partial return to myopia, but not as bad as the vision had been before without glasses.

Cutting the cornea (e.g. to create a flap or flap disc) has been around for decades. Lamellar cuts were made in the 50s, and the first mechanical keratome was first used in 1963. No long term problems were seen, except when too little thickness was left in the cornea. At my clinic, we use a high safety standard of leaving 300 microns in the corneal bed, after creating the flap with a femtosecond laser and using the excimer laser to reshape the cornea.

The main worry is in excessive weakening of the cornea. However, the incidence of bending of the cornea through weakness in post-LASIK patients is the same as the incidence of bending from a disease known as keratoconus (KC). So in normal LASIK where all the safety parameters are observed, we are not sure if LASIK actually contributes to corneal bending post-operatively.

The key here, as always, is rigorous screening pre-operatively and visiting a centre where you get sufficient time for your consultation. Some clinics do consultations in 30 minutes, or even less. Others (mine included) spend much longer. Focus consultations take at least 2 hours.

Choose carefully.

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Sandor asked this question on Lasik flap healing:

Dear Dave,
Is it true that corneal flaps never heal completely after Intralasik? What is the chance of dislocation during the rest of the patients life?
Thank you in advance, Sandor

Sandor, it’s an important question. It is true that thicker (e.g. blade, keratome) flaps never fully heal. They can be surgically lifted many years after. However, thin flaps such as are created with femtosecond lasers (around 100-110 microns) appear to heal significantly more strongly.

The healing in the uppermost layers of the cornea is different from deeper down. Collagen fibres are more wavy and heal much better when cut with a thin flap. I have found a couple of patients where I have tried to lift femtosecond flaps, and they were fully bonded down and impossible to lift after a year post-op. This has never been the case with keratome blade cut flaps which I have always been able to lift, even many years later.

IntraLasik is just the brand name for flaps made with the Intralase American made femtosecond laser. Using the Swiss Ziemer laser it is called Z-LASIK.

The key question first is the depth at which a flap was cut. One of the major reasons why many clinics have invested in femtosecond lasers over the much cheaper keratomes (10x more expensive for a femtosecond) is being able to cut predictable accurate thin flaps, with their better healing.

If it was a thin flap, e.g from a femtosecond laser (Ziemer, Intralase, Visumax, Femtec), I expect the lifetime chance of dislocation will be zero.

Here are the answers to one of today’s questions:

From Ian, who said:

A fantastic site, very informative.  A quick (but naive) question.  I am very excited about the prospect of having intra Lasik to correct a minus 5 prescription.  However, I have read some scare stories on US web sites which suggest that it is possible that the cornea can be irreparably damaged during the flap creation process.  How often have you seen this happen?

Thanks Ian. Correcting a -5.00D prescription is quite routine and should give you no problems. You mentioned IntraLASIK, which is a brand name when the Intralase femtosecond laser is used to create a Lasik flap. I don’t know whether you refer to femtosecond Lasik in general or you are looking at the Intralase machine for treatment. Manufacturers AMO now refer to iLasik rather than IntraLASIK. Other version are Z-LASIK when the Ziemer femtosecond laser is used, and Visumax and Femtec systems from other companies.

The femtosecond lasers have replaced the blade-cut keratome Lasik procedures in many clinics. One of the reasons to do this is to eliminate the possibility of a seriously damaged flap from a keratome, which I have seen happen (although it’s occurrence is rare). I have never seen this occur with a femtosecond laser and it is not possible to ‘mangle’ a flap with these technologies, so added safety.

Here is a recent question I was asked on whether LASIK is suitable for thin corneas:

“Dear David, I wrote a while ago to ask whether Z Lasik gave greater scope to those of us with thin corneas for having Lasik as opposed to Lasek or PRK. At the time, I didn’t know what my actual measurement was – I have since had my notes from my previous check and they read L 465, R 473. However, reading recent posts on your blog I see that you do not recommend any ‘flap cutting’ to anyone with a corneal thickness measurement of under 500. I suppose what I’m asking, is if that is completely set in stone? Does Z Lasik not allow you to consider previously borderline cases?“,

And another question on the same topic:

Hi Dave,
I have myopia of -6.5 and -2 for astigma. I have a corneal thickness of 490 micron. I went for 2 different consultations. One surgeon recommend that i should do PRK because he said that it is safer than iLasik (intralase) due to zero flap create. The other doctor recommended me to go with Intralase because he said that it is possible. I know that both procedures are safe. But i am just a bit concern in the long term. Also, what is the down side of having intralase over PRK or the other way around?

Average central corneal thickness is 530-540 microns. Many surgeons, myself included, don’t cut LASIK flaps in corneas less than 500 microns, although there are surgeons who will. In the first question, this person had very thin corneas (465 and 473 microns) and in my opinion should NOT have LASIK. In the second, the corneas are thin at 490 microns, but not excessively so.

It is true that being able to create very accurate LASIK flaps with the new femtosecond lasers (e.g. Ziemer, Intralase, Zeiss) leaves more tissue behind and so allowing larger treatments. More on this topic in my next post.

IMPORTANT NEWS for those people considering having LASIK laser eye surgery.

There appears to be a fundamental difference between LASIK flaps cut either with a blade or created with a laser. Laser created flaps mean a safer surgery as the results are more accurate, so fewer enhancements needed, and the eye is left stronger.

Making a replaceable flap is the first part of the LASIK procedure, just prior to reshaping the cornea to correct vision. Until recently (and still in many clinics) the flap was made by a physical cut with a very sharp razor blade contained within a precision device. However several clinics and the major three chain operators have invested in femtosecond lasers to create the corneal flap without the need for a blade.

This is known as blade-free LASIK, dual laser LASIK, Z-LASIK or IntraLASIK depending on which clinic you are talking to.

We know that thicker flaps cut with a blade do not fully heal and can be lifted up surgically even many years later. Traditional blade flaps are thicker and cut deeper into the cornea. However laser flaps are thinner and leave the eye stronger afterwards.

However a key difference highlighted by Professor John Marshall in London is that because these very thin laser flaps pass through near the surface of the cornea where the collagen is different from deeper down, they actually heal down and are not able to be lifted later on. This means the eye regains strength again with a laser flap, but not with a blade flap.

Newer blade machines have been introduced in 2008 and 2009 that cut thinner flaps to compete with the thin femtosecond laser flaps which should benefit from the better healing seen in sub-120 micron flaps

My recommendation to you when choosing a clinic is to be able to select to have a femtosecond laser procedure at a clinic that has that technology. They are more expensive than blade procedures (expect to pay around £300 more per eye) but well worth the likelihood of a long-term increase in safety.

I recently received this email with a couple of great questions:

My name is Carlo and I have recently discovered this great blog. I would like to ask a couple of questions regarding eye surgery:

a) Can the creation of a flap in the eye potentially lead to problems? Should PRK and LASEK be better in the long run for patients?
b) Is it true that the LASIK procedure has not been approved for air-force pilots and astronauts in the US but PRK and LASEK has?

There is a lot of confusion on the web about those issues. Could you spend some time clarifying that?

Let’s look at the first question now and I will address the second in a subsequent posting.
The majority of surgeons use the LASIK technique, where a thin flap is created in the top part of the cornea before applying the vision correction laser. More than 90% of laser eye surgery procedures are LASIK rather than surface laser treatments (PRK or LASEK).

There has not been any research to show signifiant differences in results between LASIK and PRK for short sight so whichever you choose to have, the final outcome will be the same. However, for long sight or reading vision correction, LASIK appears to give a more stable results and this is my preferred method for these types of prescription.

But let’s stay with short sight for the moment, where the vision and stability are not affected by the choice of procedure. It then comes down to safety. I personally used to prefer PRK over LASIK due to the small but measurable complications arising from using a blade to cut a flap. At that time, when I asked myself which procedure I would have, it would have been PRK.

However, with the arrival of the very safe and predictable laser flap makers (femtosecond lasers) I no longer subscribe to that view and would personally now choose to have all-laser LASIK. The femtosecond lasers create a very predictable and thin flap time after time, with greater precision and safety than the mechanical keratomes could. Early research also shows improved vision results, especially in reaching the very high target of better than 20/20 vision.

You still need an expert surgeon and a very thorough examination and consultation because there are points we can detect which do predict a bigger chance of having a problem in the long term. Such patients need to be screened out of the LASIK or PRK process and should not have surgery.

So choose an expert centre with an expert surgeon and you will have a safe and predictable experience and result. You can comfortably opt for LASIK over PRK/LASEK without worries for the long term.

Certainly, patients much prefer LASIK as vision is very good within a few hours (even quicker with our Z-LASIK approach) and they can be back at work the next day, rather than needing to take several days off work. Also, most patients find PRK or LASEK to be a pretty painful experience for 2-3 days after correction (the procedure itself is painless).

I get asked about the so-called ‘femtosecond‘ lasers now being used in LASIK laser eye surgery, and what these devices do. OK, here are the answers.

First of all, LASIK eye surgery is a laser procedure with two parts. First we have to make a thin flap from the top part of the cornea, basically a thin hinged layer we can temporarily fold to the side (painlessly!).

Next we use an ‘excimer‘ laser to reshape the exposed cornea to correct the vision focusing problem. The laser will polish away certain areas, depending on your prescription, to bring back clear vision.

The flap is put back in place and heals over very quickly. The eye feels gritty or scratchy for about 3-4 hours only. OK, so far so good.

For the first stage, making a flap, we have used a mechanical device called a keratome (or microkeratome). Keratomes have been around for 50 years and use a blade to make a controlled cut. This stage is where significant complications can occur, so we have been looking for a way to make this corneal flap but without the need for a blade.

Along come femtosecond lasers.

The eye lasers use ultra-short infra-red low energy pulses to create microscopic bubbles at a precise depth below the surface of the cornea. If you do this millions of times, you can create a super precise separation as a sheet, and hence a near-perfect corneal flap, which you can now fold to the side ready for vision correction with a second laser.

The femtosecond laser means we no longer run risks from using a blade to cut a flap. This means safer LASIK eye surgery.

You can watch a video of femtosecond laser eye surgery here.

More on femtosecond lasers coming soon.

Definition for femtosecond:

(This definition follows U.S. usage in which a billion is a thousand million and a trillion is a 1 followed by 12 zeros.)

A femtosecond is one millionth of a nanosecond or 10^-15 of a second and is a measurement sometimes used in laser technology. So that’s one billionth of a millionth of a second! As a comparison, one femtosecond to a second is like one second to 32 million years.

For comparison, a millisecond (ms or msec) is one thousandth of a second and is commonly used in measuring the time to read to or write from a CD-ROM player.

A microsecond (µs) is one millionth (10^-6) of a second.

A nanosecond (ns or nsec) is one billionth (10^-9) of a second and is a common measurement of read or write access time to random access memory. A picosecond is one trillionth (10^-12) of a second, or one millionth of a microsecond. An attosecond is one quintillionth (10^-18) of a second and is a term used in photon research.

[tags] LASIK, femtosecond, laser eye surgery, safety, risks, compications [/tags]

 We have been using the Ziemer LDV for 3 weeks now with great results. Vision results and flap creation have been excellent and without any complications.

For eyes with pre-existing corneal scars there has always been a question mark over the ability of femtosecond lasers to create LASIK flaps as the scar tissue may prevent the laser from passing through the tissue. Intralase users report that they found an inability perform LASIK to treat eyes that have pre-existing moderate to dense corneal scars.

Unlike the Intralase (American made femtosecond eye laser), the Swiss-made LDV will pass through even fairly dense corneal scars without a problem. So far the LDV has created excellent flaps in these cases. I will keep you updated on our progress.

[tags] laser eye surgery, complications, femtosecond, flap, Intralase, LASIK, risks, safety, Z-LASIK, Ziemer [/tags]