Preoperative evaluation key to finding risk of ectasia after LASIK

A new assessment model can effectively assist in selecting patients for refractive surgery, physician says.

PARIS – Careful preoperative assessment of basic parameters can help predict ectasia risk after LASIK in more than 90% of cases, a surgeon said.

Since the first case, described by Theo Seiler in 1998, iatrogenic ectasia has become a big concern for refractive surgeons. However, its actual incidence has never been precisely quantified. It is estimated to be between 0.2% and 0.6%, Thanh Hoang-Xuan, MD,of American Hospital of Paris, said at the annual meeting of the French Society of Ophthalmology.

“Our practice must always be founded on evidence-based medicine,” Prof. Hoang-Xuan said.

When a patient comes for a refractive procedure, caution and an accurate preoperative evaluation are mandatory, he said.

To determine ectasia risk, Prof. Hoang-Xuan said surgeons should critically read and evaluate the studies available in the literature, keep constantly updated with them and rate their credibility on the basis of the methods that were used.

A new ectasia risk assessment model

An article by Randleman et al provides refractive surgeons with a useful ectasia risk assessment model to assist in selecting refractive surgery candidates, Prof. Hoang-Xuan said.

“Dr. Randleman’s system is based on a review of 171 cases of iatrogenic ectasia published since Dr. Seiler’s first report. He listed a series of four preoperative parameters in order of importance: topography, predicted residual corneal bed thickness, age and preoperative spherical equivalent,” he said. “And on the basis of these, he developed a risk score model, assigning a point value to each of these factors, leading to a 0 to 4 stratification of the level of risk for ectasia.”

In the patients at low risk for ectasia (level 0 to 2), LASIK or PRK with mitomycin can be performed. With patients at moderate risk (level 3), the potential hazards of a LASIK procedure must be discussed and a clear informed consent must be signed. In this category, there is also no evidence that surface ablation will be completely safe. In high-risk patients (level 4), LASIK is contraindicated, and because the evidence of safety for surface ablation is not proved, an informed consent is required, Prof. Hoang-Xuan said.

PRK is a low or no-risk procedure

Prof. Hoang-Xuan said Dr. Randleman’s system is a good tool for the refractive surgeon and only requires topography and pachymetry facilities. He told the audience how this system guided him in deciding to perform PRK rather than LASIK in one patient with a risk score of 3 and to abstain from surgery in a risk 4 case.

Other risk factors can be evaluated before suggesting the appropriate treatment, such as preoperative visual stability, a family history for keratoconus and lack of enantiomorphism. Placido and elevation topography maps, as well as aberrometry, will provide additional information, and the ocular response analyzer will add data on elasticity and resistance. Therefore, the risk for ectasia can be minimized.

The 4% incidence of ectasia after PRK is about the same in eyes that did not have any refractive surgery procedure, he said.

“Some of those patients would have developed keratoconus, also, without the refractive treatment,” Prof. Hoang-Xuan said. – by Michela Cimberle

For more information:

Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology. 2008;115:37–50.