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Post Info TOPIC: PRK With X Linking


Senior Member

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Posts: 124
Date: Tue Nov 13 7:34 PM, 2007
RE: PRK With X Linking
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Evening Yarsky,

I performed the treatment(Topoguided PRK and Crosslinking) combined together.This approach is the best.The epi is going off one time,the cornea hasnt crosslinked until topo-PRK is performed and then the xlinking is taking place right afterwards.Thats the treatment with a few words.

Before this approach,we had first the collagen crosslinking and then WAIT 6 months for the topographies to show the stop of kc and then perfoming the limited topography guided PRK.

Since the results are all stable 5-6 years now the first method gives better visual results.I know all this stuff from my doctor.So,thats why i perfomed both of them at the same visit and not wait six months.Its your choice though.

I wouldnt do AND I AM SAYING IT AGAIN,it wouldnt cross my mind to do this procedures NOWHERE in the world except from Doctor Kanellopoulos.Believe me Yarksy he knows what is doing and if you are a candidate for this procedure.

Certainly you can perform the limited topography guided PRK if you are a candidate and you dont need to perform again crosslinking my friend because you have already performed it.It all depends from your thickness.

If you want the treatment you need to come here and visit Dr K.I dont think thats a good idea to search elsewhere because simply doctors dont know how to perform the treatment.Dont play with your eyes as i wisely want to say.

Dr Kanellopoulos results and me as i am here and talking with you my experience shows that.Also,Cloudd should speak more to the forum to tell us how he sees now.Come on Cloudd,Come to the forum mate.

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Senior Member

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Posts: 139
Date: Tue Nov 13 7:34 PM, 2007
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Thanks

I guess i made my previous post about prk and crosslinking...it seems it could be good..but i had a few concerns...mainly that scarring might be a contraindication for any treatment other than contacts[as i don't need a graft i am excluding that as a treatment option ]

right now i guess i am going to have to try and find out from my opticien how bad my cataracts and the moderate kc is? I have not got a clue about the thickness of that cornea or if it stable or not[like i said i am not sure if it is cataract or kc causing prescription changes]

Unforutately it may be that i do not have any treatment options other than contact lens in my case...i will look into c3r to see if i am eligible for that to stop kc getting worse[then again if my kc is stable ??/ why bother?] i have so many unknowns that i will have to quite frankly ask my opticien how bad kc and cataracts are

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Executive

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Posts: 437
Date: Fri Nov 16 2:19 AM, 2007
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Dear Zeus, I have no doubts about the fact that it works and the results are positive. My only preoccupation is to understand how does it work, in the most detailed way. As far as I see from the internet articles, the PRK acts on the Bowman layer, as you said. It vaporizes a part of it. Then x_linking is done to fix the whole thing. Bowman layer is very thin, 10µm. If one's deformation is serious, one may need to vaporize much more than 10 µm. So, to me, the outcomes of the procedure are in a direct link with the stage of one's KC. If it is an onset - one may not need the PRK at all, just x_linking; if it is stage 2, then, well, ptobably one may be well better off with the combination of the two. If, now, it is stage 3, the cornea is ruther deformed and PRK correction, if it acts on the Bowamn layer only, may not be enough: to correct it well one would need to prk more layers of the cornea...It is then said that even if more layers are prk'ed, the x_linking guarantees the permanent stability of the treated cornea. Very reasonable to me. But a) I think only corneas with no less than 4-500 µm thickness can profit form the combination of the two treatment (for how thin does the cornea become after PRK? What would the corneal thickness be after the PRK) b) the post op evolution of the corneal morphology is not very well undestood and controled at this moment of history (even if the op itself is wavefront guided), so that the outcome with respect to the vision acuity is a bit arbitrary, even if it is not arbitrary wrt to the general corneal health.

-- Edited by Yarsky at 02:24, 2007-11-16

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yarsky


Ophthalmologist

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Posts: 18
Date: Fri Nov 16 8:23 PM, 2007
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Dear friends:

As an ophthalmologist i will make you some historical comments that can facilitate you to understand how laser refractive corneal procedures biomechanically work.

PRK was the initial form to apply the excimer laser to correct myopia and/or astigmatism in late 80´s. After removing the epithelium, the laser vaporizes ( not reshapes) the Bowmann´s membrane, which is only 10 to 20 microns thick and the superficial stroma ( collagen and stroma dense in keratocytes). The problems were; old wide spot lasers created central islands, ablations were rough and activation of keratocytes induced haze ( scar) if myopia was higher than 4-6 diopters. Biomechanically the cornea was not affected and no report of ectasia was published.

LASIK was introduced in the early 90´s and refractive results improved so much. BUT, we saw that what really keeps biomechanically the shape of the cornea ( I simplify the words for better understanding) and prevents the ectasia ( bulging) is the residual bed left after the excimer laser ablation.

So PRK results in a "thicker" effective cornea to prevent ectasia. If in a cornea of 500 microns you perform an ablation of 75 microns with PRK, you´ll have an "effective" residual cornea of 375 ( 500-50 microns of epithelium-75= 375) If you perform the LASIK technique ablating the same amount of tissue but 110 microns deeper ( using for example a femtosecond laser to create a 110 microns flap) you will have an effective residual cornea of 315 microns ( 500-110-75= 315) With LASIK you preserve the Bowman´s and the superficial keratocytes, so you don´t have haze, but you weaken the corneal structure more than with PRK.

That´s why ectasias started to appear 10 years ago. We didn´t know which were the limits of LASIK ( despite Barraquer described 60 years ago the limits for the old keratomileusis procedure saying that the minimum residual bed was 250 microns...) Now we don´t treat more than 9 diopters of myopia.

There have been a lot of research on corneal ectasia after LASIK. You know that refractive surgery is a huge global busisness today and a lot of money have been invested in make it safer and safer. We all agree that the most important risk factor for developing ectasia after LASIK is having an undiagnosed keratoconus, which could be in its initial stages and not diagnosed yet. That´s why a lot of research in the keratoconus field has been made, fortunately for KC patients that, until then, had been only treated with CL or corneal grafting.

Seiler was the first in publishing a paper about ectasia and I´ m sure he developed crosslinking for treating this terrible complication of LASIK surgery. KC patients have benefit of the advances and the better understanding of the complications in refractive surgery as you can see.

PRK ( now called ASA advanced surface ablation) is coming back. We´ve seen the LASIK problems the last ten years and the we prefer now to perform PRK,with better flying spot lasers than before, in patients with low myopia ( I personally perform PRK up to -4, not more) and always discussing with patients the two types of surgery. Some patients prefer LASIK, others PRK. In thin corneas with no KC signs it´s mandatory to use PRK.

That´s why performing PRK in a crosslinked cornea could be an option for patients in which the refraction is not high and the amount of tissue to be ablated is not more than 50 microns, or the residual corneal thickness will not be less tha 400 microns. Crosslinking will make the cornea more rigid and the weakening effect of PRK ( which was initially contraindicated in KC patients) The use of mitomicyn C will prevent the haze formation which is specially higher in KC young patients. Time will elucidate if it´s better to perform the procedure simultaneously or sequentally.

Two days ago a new technique of crosslinking was described in the American Academy of Ophthalmology meeting by Dr Kallenopoulos in which he cuts the cornea with the femtosecond laser creating a pocket 100 microns deep in the corneal stroma WITHOUT cutting the bowmanns ( the femtosecond laser allows to do almost any kind of cut inside the cornea) and therotecally it will increase the penetration of riboflavin and he only uses 15 minutes of UV exposure.

And in response to Geraldine´s problem, if the keratoconus is stable, your age is "older" than 40 or 50 years and you have cataract, there´s the possiblity to correct the refraction performing the cataract surgery implanting a intraocular toric lens which can correct the myopia and the astigmatism created by the conus ( only if your conus is not highly aberrated, obviously) In Germany the can "custom made" Intraocular lenses up to -15 diopters of astigmatism (Micro Sil toric IOL from Dr Schmidt intraocular lenses company).

Hope this long post serves.
Good night



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Juan


Phase Two

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Posts: 484
Date: Fri Nov 16 11:45 PM, 2007
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Juanito, Thanks so much for your very well thought out post and your medical expertise which you kindly share with us. We apprishiate it alot. It's always good to hear from you, you are a loyal friend to these boards and a very much valued member.

Thanks again

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Executive

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Posts: 437
Date: Sat Nov 17 1:45 AM, 2007
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Juanito!!! Your insight is extremly valuable! Thanks a lot!

-- Edited by Yarsky at 01:46, 2007-11-17

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yarsky


Senior Member

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Posts: 124
Date: Sat Nov 17 4:20 AM, 2007
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Hello everyone,

I would like to thank Doctor Juanito for his post.

I misunderstood about the Bowmans layer.In Lasik this membrane or layer is preserved.In PRK this membrane or layer is vaporized.

I want to ask Doctor Juanito: The topography guided PRK treatment is being applied at the periphery of the cornea TECHNICALLY LIKE A HYPEROPIC treatment,NOT CENTRAL,is bowmans layer vaporized?

Because the treatment i had,it is not a straightforward PRK.It is not Wavefront guided,it is NOT CENTRAL.

It is Limited,It is TOPOGRAPHY(NOT WAVEFRONT),it is with FLYING SPOT BEAM and it is made with a special NOMOGRAM.Also, the laser that reshaped my cornea is BUILT FOR ASPHERIC CORNEAS.400hz Wavelight EYE Q ALLEGRETTO flying spot laser.My topography taken out by the PENTACAM and the SCIENTIFIC DATA put it in the software of the laser.

Yarsky my friend i am not a doctor.Your questions are really interesting and at the heart of the PRK issue.All i can say is my experience and the little information i know.Send an Email at Doctors Kanellopoulos Institute.

Dr Juanito,I performed the treatment combined together.Meaning FIRST THE LIMITED PRK and then right afterwards the xlinking.

If i had choose first the crosslinking and then wait 6 months LATER the TOPO-PRK i would have face some barriers and difficulties.Such as:

a)Epithelium taken off twice.
b)With the laser i would have UNDERCUT some of the mechanical STRENGTH-stability which i gave with the CROSSLINKING.
c)More Possilbe Haze because of the rigid cornea.
d)Could NEVER do an enhacement retreatment.

So,considering all the above i think the best approach is TO COMBINE THE TREATMENTS TOGETHER.As my doctor says:You will have gratifying results..

All the best,



-- Edited by Zeus at 04:38, 2007-11-17

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Member

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Date: Sat Nov 17 11:57 PM, 2007
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I´m not sure of the suitability for performing the topography-guided PRK but for me the main concern would be that reduces the integrity of the cornea vaporizing around 30-40microns(not 100% sure of the figure).

Just want to add that for post-lasik ectasia patients, like me, the treatment could still be performed, even with the reduced cornea after the lasik the good news is that the cornea removed will be the one in the flap which doesn´t add any integrity anyway.

epithelium off (50mic) + PRK (30-40mic) < flap (around 100)

Even in kc patients this small amount of tissue removed won´t probably affect at all a crosslinked cornea.

My main doubt about the treatment is if offers better results than INTACS implants. I think it does and that´s why I´m looking forward to do this treatment in the future.

I think is a promising treatment and there are a good margin of improvement over the next years. It seems the development of better screening machines is going fast.

About performing the treatment about the same time my main objection will be that the crosslinking can induce changes in the cornea after the operation that could result in worse visual acuity.

About performing first a crosslinking and then the PRK the main problems for me are to undergo two operations with epithelium removal (minor problem for me) and being able to do the correct PRK in a crosslinked cornea with abnormal rigidity.

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