Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening

Abstract

Purpose: To validate the Ectasia Risk Score System for identifying patients at high risk for developing ectasia after laser in situ keratomileusis (LASIK).

Design: Retrospective case-control study.

Methods: Fifty eyes that developed ectasia and 50 control eyes with normal postoperative courses after LASIK were analyzed and compared using the previously described Ectasia Risk Score System, which assigns points in a weighted fashion to the following variables: topographic pattern, predicted residual stromal bed (RSB) thickness, age, preoperative corneal thickness (CT), and manifest refraction spherical equivalent (MRSE).

Results: In this series, 46 (92%) eyes with ectasia were correctly classified as being at high risk for the development of ectasia, while three (6%) controls were incorrectly classified as being at high risk for ectasia (P < 1 x 10(-10)). Significantly more eyes were classified as high risk by the ectasia risk score than by traditional screening parameters relying on abnormal topography or RSB thickness less than 250 micro (92% vs 50%; P < .00001). There was no difference in the sensitivity or specificity of the Ectasia Risk Score System in the population from which it was derived and this independent population of ectasia cases and controls.

Conclusions: The Ectasia Risk Score System is a valid and effective method for detecting eyes at risk for ectasia after LASIK and represents a significant improvement over previously utilized screening strategies.

Figure 1. Comparison of Screening Results Utilizing the Ectasia Risk Score System and Traditional Screening Parameters for Identifying Patients at High Risk for Developing Ectasia after LASIK

Ectasia screening comparisons for ectasia cases utilizing the Ectasia Risk Score System (Ectasia Risk Score) and (Traditional Parameters). The Ectasia Risk Score System correctly identified a significantly greater percentage of eyes than traditional screening methods (abnormal topography or residual stromal bed less than 250 microns) that ultimately developed ectasia (92% vs. 50%, p<0.00001) with very few false negatives (8%).

Figure 2. Ectasia Risk Score System Score Comparisons Between the Ectasia and Control Populations from This Study and Previous Study for Identifying Eyes at High or Low Risk for Developing Ectasia after LASIK

Eyes from the previous study population* were labeled as Ectasia 1 and Control 1, and eyes from this study were labeled Ectasia 2 and Control 2. There were no significant differences between ectasia cases from the two populations or controls from the two populations in percentage of eyes identified as low or high risk. *Previous study population was reported in Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk Assessment for Ectasia after Corneal Refractive Surgery. Ophthalmology 2008; 115: 37-50.

Figure 3. Receiver Operated Characteristic (ROC) Curve Comparing Sensitivity and Specificity for the Ectasia Score System in This Study and Previous Study Populations in Screening for Eyes at High Risk of Developing Ectasia after LASIK

The steep rise in both curves demonstrates high sensitivity and specificity for both populations, the previous study (Series 1) and this study (Series 2), and there are no significant differences between the two groups.

Figure 4. Distribution of Ectasia Risk Score Points by Category for Ectasia Cases Using the Ectasia Risk Score System for Determining Eye at High Risk of Developing Ectasia after LASIK

This graph demonstrates the percentage of ectasia cases that scored each point values for each parameter evaluated in the Ectasia Risk Score System. RSB = Residual stromal bed thickness CT = Preoperative corneal thickness MRSE = Preoperative spherical equivalent manifest refraction