Is SBK Really on the Market?

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Is SBK Really on the Market?

Postby techn0mad » Thu Dec 06, 2007 1:48 am

I've been researching Lasik casually for some months, and very intensively during the past week.

I've selected a surgeon that I have some level of trust in, and I've been through all of the pre-screening and pre-operative steps. I had a chat with the surgeon today and I explained that my research thus far shows the following: Commercial LASIK is getting increasingly predictable and routine, with respect to the visual/optical outcomes. However, the 800 pound gorilla in the room is the fact that nobody is able to predict how any given individual's eyes will react to being injured (which is how our corneas interpret any kind of refractive surgery). This is why nobody can offer any sort of legitimate guarantee of results for LASIK surgery.

Anyhow, my biggest concerns with conventional LASIK have to with Corneal healing and biomechanics. Slicing the top of the Cornea off (to make the flap) makes it less mechanically stable, and from what I've read, the flap will never completely reattach to the underlying stroma. There are also lots of problems that appear at the wound edge (epithelial ingrowth, etc.). Add to this the potential complications related to neuropathy, like dry-eye and so on and I begin to get uncomfortable.

So my surgeon said "Have you heard of SBK?". I said that I had seen mention of it but I didn't know what it was. He explained that it was a kind of hybrid between PRK and LASIK, where a very thin flap is made, presumably just below the Bowman's layer near the top of the stromal tissue. It is argued that this technique provides the benefits of PRK by disturbing less of the stromal tissue and preserving more of the Corneal posterior at the same time as the benefits of LASIK such as a more comfortable surgery and faster healing.

I then asked if he performs this procedure, and he said that basically all of his LASIK procedures are done this way. I asked how thick the flap he would create would be in my case (I have relatively thick corneas) and he said 110 microns.

I was scheduled to have my surgery tomorrow but I deferred it to next week, partly because I haven't made up my mind completely yet, and partly because I wanted to research SBK some more.

Does anyone know if SBK is being done as a routine procedure these days? From what I've seen, the results of clinical trials have only been published earlier this year, so I'm a bit skeptical of claims that people have this "in production" already. Another issue is the definition. From what I've read, "old school" LASIK with microkeratomes used flaps in the range of 150-220 microns. FS laser keratomes have improved this range, and my surgeon says that he creates a 110 micron flap. Published papers about SBK discuss flaps in the range of 70 microns. So, if SBK is a "thin flap" procedure, what constitutes a thin flap?

My understanding is that state of the art is LASIK using a FS laser keratome followed by an iris tracking, custom wavefront guided excimer laser. Again the question is: If the flap created in such a procedure is thin enough, does this procedure become SBK? If so, how thin does the flap have to be?

Any/all responses appreciated.
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Postby SteveR » Thu Dec 06, 2007 9:35 am

Hi techn0mad,

Just to let you know my LASIK (FS) flap was 120 microns. If you go for something new (i.e. 70 micron flaps) then you'd have to weigh up the pros of going for something possibly better but less well tested versus the devil you know. (For example risk of flap tears, ease of lifting for retreatments, etc). I take it your prescription rules out a surface technique (PRK, LASEK, etc)?
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Postby techn0mad » Thu Dec 06, 2007 7:27 pm

SteveR wrote:Hi techn0mad,

Just to let you know my LASIK (FS) flap was 120 microns. If you go for something new (i.e. 70 micron flaps) then you'd have to weigh up the pros of going for something possibly better but less well tested versus the devil you know. (For example risk of flap tears, ease of lifting for retreatments, etc). I take it your prescription rules out a surface technique (PRK, LASEK, etc)?


Hi SteveR:

My understanding is that the lower limits on the flap thickness indeed include issues like ease of handling the flap, increased likelihood of "buttonholes", and getting too close to Bowman's layer and the epithielium. I presume that the overall idea of SBK is to get the benefits of LASIK and PRK combined.

My prescription does not rule out PRK/LASEK, it's actually reasonably mild (~ -5D). However, my surgeon explained that the potential complications of surface techniques are no less likely than the potential complications of conventional LASIK. He simply says that he is using SBK techniques because they minimize the risk of complications and provide the best balance of results and patient comfort. I certainly like the idea of it simply because it minimizes the biomechanical changes to the Cornea without having to deal with the wound healing complications of surface techniques.

However, my problem is that the term "SBK" is not very well defined yet. I don't know if a 110 micron flap constitutes SBK or not. From what I've read so far, it seems that in the refractive surgery industry, what a term means is often left to marketing people, and that makes me uncomfortable. On top of this, there seems to be a growing PR war between the FS laser folks and the Microkeratome folks, since my understanding is that it is more or less impossible to safely make <100 micron flaps with a mechanical keratome.

One more thing that came to mind: There may be regulatory issues here. I have no idea what the range of flap thicknesses that the IntraLase FS laser is approved for by the FDA. It could be that either the software or the regulations (or both) prohibit using the device to make thinner flaps outside of a clinical research setting.

Cheers,
techn0mad
 
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Postby LasikExpert » Thu Dec 06, 2007 8:06 pm

The term SBK was created as a descripter of thin flap Lasik. There is no specific definition of SBK other than Lasik with a relatively thin flap. One of the early developers of this term recently stated that about 100 microns would be SBK. He also stated that SBK can be acheived with a femtosecond laser such as the Intralase or a traditional mechanical microkeratome.
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Postby techn0mad » Thu Dec 06, 2007 8:12 pm

LasikExpert wrote:The term SBK was created as a descripter of thin flap Lasik. There is no specific definition of SBK other than Lasik with a relatively thin flap. One of the early developers of this term recently stated that about 100 microns would be SBK. He also stated that SBK can be acheived with a femtosecond laser such as the Intralase or a traditional mechanical microkeratome.


Hi Glenn:

Can you provide a reference to where this statement was made?

P.S. Thanks for providing such a great resource for LASIK customers (actual and potential).
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Postby SteveR » Thu Dec 06, 2007 8:43 pm

Actually on my rereading your post it seems that your surgeon is going for a 110 micron flap, rather than a potential 70 microns (my bad). 110 microns is well with the range I recall being informed of at my consultation (I think it was between 90 and 120 microns), so my feeling is that the 110 microns earmarked for you is pretty bob-standard, and the term “SBK” a bit redundant, at 110 Microns. I don’t know why I ended up at the top of my quoted range at 120 microns (I had relatively thick corneas though), and I doubt many all-laser (FS/intralase) LASIK flaps are in the 150-220 microns range.

Good luck!
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Postby techn0mad » Thu Dec 06, 2007 9:06 pm

SteveR wrote:Actually on my rereading your post it seems that your surgeon is going for a 110 micron flap, rather than a potential 70 microns (my bad). 110 microns is well with the range I recall being informed of at my consultation (I think it was between 90 and 120 microns), so my feeling is that the 110 microns earmarked for you is pretty bob-standard, and the term “SBK” a bit redundant, at 110 Microns. I don’t know why I ended up at the top of my quoted range at 120 microns (I had relatively thick corneas though), and I doubt many all-laser (FS/intralase) LASIK flaps are in the 150-220 microns range.

Good luck!


Hi SteveR:

I guess that was part of the whole question in my initial post. I agree with you that 110 microns is not a particularly thin flap, so my surgeon is pulling my leg when he says that he "does" SBK. This does not help with my feeling of not getting the whole picture from him...

Cheers,
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Postby LasikExpert » Thu Dec 06, 2007 10:46 pm

The reference was presented a few weeks ago as part of an open free paper presentation at the annual conference of the American Academy of Ophthalmology in New Orleans. The presentation was sponsored by Allergan, which has no direct interest in SBK.
Glenn Hagele
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Postby techn0mad » Thu Dec 06, 2007 11:00 pm

LasikExpert wrote:The reference was presented a few weeks ago as part of an open free paper presentation at the annual conference of the American Academy of Ophthalmology in New Orleans. The presentation was sponsored by Allergan, which has no direct interest in SBK.


Thanks Glenn!
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