When is a Cornea Too Thin for LASIK?

Femtosecond Lasik Flap CreationHere 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.

Filed Under: LASIKSafety

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About the Author: Mr. Dave Allamby FRCS FRCOphth is a leading London-based laser eye surgeon. You may have seen him on the This Morning TV show with Phillip Schofield and Fern Britton or read one of several articles in the national press, recently for treating Denise Van Outen, rock giant Rick Wakeman and broadcaster Paul Ross. David is Medical Director at Focus Laser Vision, known as a world-leading clinic in the treatment of presbyopia, or age related loss of close vision. Focus Laser Vision is also London's only clinic to offer next-generation Z-LASIK laser eye treatment for short sight, long sight or astigmatism.

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  1. Hi dave,i have recentley had a consultation with optical express,and was told that i am suitable for lasik acv Ifs surgery,my perscription is -7.50 in both eyes and both corneas are 515 microns,after researching about the procedure i am concerened that my corneas are to thin and i am worried about my eyes developing a bulge or swelling long term,just need some reasurance…thanks mandy

    • Dave Allamby says:

      Hi Mandy
      A fewf points here. You have to check the calculation at your clinic for how much thickness will remain in the cornea after the flap is made and the laser performed. We call this the “bed thickness”. You want to make sure that the bed is at least 300 microns thick after treatment. Some clinic use the older thinner standard of leaving down to 250 microns residual thickness. Did they discuss this with you?
      Secondly, you want your clinic to confirm what is called the ablation depth, ie how many microns they will remove to treat your full prescription. Some lasers do remove more than other, so it is worth checking when you want to preserve the maximum strength afterwards. Especially for large prescription like yours. I can let you know what our WaveLight laser would remove if you give me the full prescription, which is usually the lowest of all the lasers out there.
      Thirdly, your risk of your corneas weakening afterwards is primarily linked to the appearance of the topography scans, ie the shape of your corneas pre-op. It is looking for pre-existing signs of corneal weakness or disease, and such patients should not be offered LASIK. I would want to see my own scans before I could comment on that, ie coming to see us for a consultation.
      Hope that helps!
      David

  2. Petrina Durant says:

    Dear David

    I went for an appointment with focus vision about three years ago and was refused treatment because my corneas were considered too thin. The optometrist recommended I try ultralase but advised against lasik. I recently went to ultralase and they are happy to perform the surgery they’ve said that new technology means they can cut a very thin flap. My prescription is -5.25 and my corneas are about 460 microns. My prescription is not suitable for lasek. The alternative is ALI implants. I haven’t spoken to my surgeon yet but I am in constant contact with the optometrist who has emphasised that they wouldn’t peform the surgery if it was unsafe. I’d welcome your thoughts. I have large pupils – not sure if that’s relevant and I’m going for the ‘lasik ultra elite’ option with monovision.
    Petrina

    • Dave Allamby says:

      Hi Petrina, At 460 corneal thickness I would certainly not recommend LASIK. We can also cut thin femto flaps, as can most clinics, but we only perform PRK/LASEK for thinner corneas. For LASIK, most specialists would want to leave a residual thickness of 300 microns or more after the flap has been made and following the (thinning) laser correction, as they believe this is safer. We also have a limit of 300 for safety. With your numbers for LASIK, even with a thin flap, you do not have enough tissue for a full correction without going thinner than 300 microns. So for me that is two strikes against performing LASIK.
      Also, what was the reason for not being suitable for PRK/LASEK?
      thanks, David

      • Petrina says:

        Many thanks for your response. If my prescription was lower say -4 they would perform lasek. they’ve said that I would suffer from halos (perhaps the large pupils?) and would need to take MMC which they described as a powerful drug to combat this. Focus vision also said they wouldn’t treat me for lasek but said to try ultralase. ultralase have said the other option is the ALI implant. I’m not sure what that’s about. I was all set to go ahead with my surgery next week but I’m going to cancel it. I am disappointed as I’m finding lenses less tolerable and my optician says they’re running out of options. Anyway better to be safe. Thanks again. This is an excellent site.

  3. prabhjot dhody says:

    hi….i have cornea thickness of 480…and have been advised for bladless lasik surgery ….please advise is it safe or is my cornea too thin

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