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An Ectasia Risk Factor Score System developed by researchers at Emory University appears to be a valid method for identifying patients at risk for ectasia after LASIK, according to a retrospective review of 171 cases of post-LASIK ectasia and 186 controls with normal postoperative courses.
The model was developed based on analysis of data collected in a retrospective review of 171 cases of post-LASIK ectasia and 186 controls with normal postoperative courses. When applied to that cohort, the scoring system identified 98% of controls as being at low risk for post-LASIK ectasia and 93% of the patients with ectasia as high risk.
Subsequently, the model was tested and validated in a novel LASIK patient population consisting of 50 ectasia cases and 50 controls. In the validation study, the predictive ability of the risk scoring system was nearly identical to that observed in the initial population, said Dr. Randleman, assistant professor of ophthalmology, Emory University, Atlanta.
"Our aim in conducting this research was to evaluate the validity of the purported risk factors for postoperative ectasia and to try to create a model to identify better at-risk patients who should be excluded from surgery," he continued. "We believe the scoring system we created represents a significant improvement upon previous screening techniques. However, surgeons should be aware its validity has been tested for identifying eyes at risk for post-LASIK ectasia and has not been established for use in screening patients for surface ablation."
The 171 ectasia cases included in the initial study were identified from records of patients seen at Emory University who had post-LASIK ectasia and through a literature search. All controls were operated on at Emory University. To be included, the control eyes needed to have at least 1 year of follow-up available, and all eyes needed complete preoperative data, including patient age, gender, manifest and cycloplegic refractive spherical equivalent, corneal thickness, best spectacle-corrected visual acuity, and topographic patterns. Other data extracted included predicted residual stromal bed (RSB) thickness.
For the study, the topographic patterns were divided into three major categories-normal/symmetric, suspicious, and abnormal, with the suspicious category including two subcategories.
"The definitions were based on Placido-based imaging because that was the type of technology used in the majority of our cases," Dr. Randleman said.
Normal topography was defined as round, oval, or symmetric bowtie patterns. Suspicious topography included eyes with either an asymmetric bowtie pattern or an inferior steep or skewed radial axis. Eyes with keratoconus, pellucid marginal corneal degeneration, or forme fruste keratoconus were categorized as having abnormal topography.
Through multivariate logistic regression analysis, factors identified as being most important in differentiating the ectasia cases from control were (in descending order) abnormal topography, predicted RSB, young age, and low preoperative corneal thickness. The topography pattern, RSB thickness, age, preoperative corneal thickness, and preoperative mean refractive spherical equivalent were used to develop a risk factor stratification model in which each parameter is assigned a point value (range, 0 to 4) and the cumulative score determines the patient's risk level as low, moderate, or high risk.
According to the model, an eye with a total score of 0 to 2 is considered low risk and acceptable for undergoing LASIK. Moderate risk is defined by a score of 3.
"For these eyes, we believe it is all right to proceed with LASIK with caution and that it would be prudent to consider a more specific informed consent along with other possible predisposing factors, such as refractive stability, eye rubbing, and family history," Dr. Randleman said.
Eyes with a cumulative score of 4 or more are considered at high risk for post-LASIK ectasia. The management recommendation for these eyes would be to exclude them from LASIK.
"Our study does not establish the safety of PRK for patients at either moderate or high risk of postoperative ectasia because we did not have enough data to analyze that outcome," he said.
The risk assessment study recently has been published (Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology. 2008;115:37-50).