Evaluation of Role of Age, Residual Stromal Bed, and Percent Tissue Altered in Ectasia Risk Assessment for Patients With Normal Preoperative Topography
Purpose
To evaluate the efficacy of a modified risk formula to assess ectasia risk in patients with normal corneal topography.
Methods
Retrospective case-control study of 30 eyes from 16 patients with bilateral normal preoperative Placido-based corneal topography who developed ectasia after LASIK (Ectasia Group) and 174 eyes from 88 consecutive patients with uncomplicated LASIK and at least 3 years of postoperative follow-up. The following metrics were used to create the modified risk formula: age, residual stromal bed (RSB), and the Percent Tissue Altered (PTA), which is derived from flap thickness plus ablation depth divided by preoperative corneal thickness.
Results
Using the formula with weighted adjustments for age, RSB, and PTA, and assigning the worst score from either eye as the overall patient score for both ectasia and control groups, all ectasia patients were correctly identified as high risk (100% sensitivity), while only7% of controls were misidentified as high risk (93% Specificity).
Conclusion
In patients with normal preoperative Placido topography, a weighted formula incorporating age, RSB, and the Percent Tissue Altered (PTA) yielded good sensitivity and specificity in ectasia risk screening.