LASIK and Risk for Ectasia: Thin Corneas, No Problem

American Academy of Ophthalmology 2012

William B. Trattler, MD


November 20, 2012

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Risk Factors for Post-LASIK Ectasia

Hello. I am Dr. William Trattler, Director of Cornea at the Center for Excellence in Eye Care in Miami, Florida. Welcome to Medscape Ophthalmology Insights. I am here at the American Academy of Ophthalmology (AAO) meeting in Chicago, and I wanted to share some of the latest developments in refractive surgery.

One of the hottest topics that is still being discussed is the risk factors for post-LASIK ectasia. Which patients should undergo LASIK, and which patients should we inform are not the best candidates for LASIK and should either have another procedure (such as photorefractive keratectomy) or no surgery at all?

The most common and important risk factor to identify is with the corneal topography. Whether we are using Placido disk topography or if we are using Pentacam® (Oculus®; Arlington, Washington) or the GALILEI™ (Zeimer USA; Alton, Illinois), which gives a different type of view, the key is that we are trying to get a good understanding of the corneal shape, to understand the strength of the cornea to predict whether the patient will be a safe candidate for LASIK or whether we should tell the patient to not have surgery at all.

With both topography and Pentacam, for example, we are looking for corneal symmetry. We want both eyes to look exactly the same and have very similar amounts of corneal astigmatism. We want them to be relatively symmetrical. Obviously, no 2 eyes are identical, but if 1 eye has a lot of astigmatism and the other eye has very little astigmatism, or if the axes are very different, you should definitely take a second look to make sure that there are no other warning signs for whether these patients are appropriate candidates for surgery.

Once we confirm that the topographies are normal, we can then look at other parameters to see whether patients are good candidates. Dr. Steve Schallhorn has shared that patients who are younger may be at slightly increased risk for ectasia, even if the topographies are normal, so that is one group we have to be aware of, but in general the risk is very low. He estimates that the risk is about 1 in 2600, so we don't want to exclude all of our younger patients because many are appropriate candidates for surgery.

How Thin Can We Go With LASIK?

The second topic that I want to discuss today is, how thin can we go with LASIK? There is a "myth" that patients who have a corneal thickness of 500 microns or less are not good candidates for LASIK, and, in my opinion, there is no good scientific evidence that this is true. There are peer-reviewed studies in which LASIK has been performed in corneas that are thinner than 500 microns, and they have shown that there is no increased risk for ectasia in that subgroup.

When we look at patients who have developed ectasia, the biggest risk factor is abnormal topography. The second risk factor is younger age, but we don't really see many patients with bilateral normal corneal topographies, that are also thin, who have developed ectasia.

I see no scientific evidence that thinner corneas place patients at increased risk for ectasia if the topographies are normal. That is why I, like many other surgeons, feel that it is appropriate to perform LASIK in patients who have a 460-470 micron corneal thickness, assuming that we also measure the intraoperative pachymetry and that we end up with a normal residual stromal bed. Those patients should be at no increased risk for ectasia compared with another group.

In fact, if you look at patients who have developed ectasia, in my experience about 85% have a corneal thickness of 500 microns or more, so it is much more common to see thicker corneas develop ectasia than thinner corneas.

Everybody wants to do everything they can to avoid ectasia for their patients, and I feel the same way. I want my patients to have a great result and I don't want to see ectasia in my practice, but I truly do not believe that avoiding patients with thinner corneas who have bilateral normal corneal topographies will reduce your risk for ectasia, and that is why I feel very comfortable performing LASIK in these patients. If you look at the scientific evidence, you will feel the same way.

I hope this is a very interesting and informative piece of information about risk factors for ectasia. Thank you for joining us today. I'm Dr. William Trattler for Medscape Ophthalmology Insights.