Role of Percent Tissue Altered in Post-LASIK Ectasia in Eyes With Suspicious Topography
Purpose
To investigate the association of a novel metric, Percent Tissue Altered (PTA), with the occurrence of ectasia after laser in situ keratomileusis (LASIK) in eyes with suspicious corneal topography and to compare this metric with other recognized risk factors.
Methods
This retrospective case-control study included 58 eyes with suspicious preoperative Placido-based corneal topography that developed ectasia after LASIK (Ectasia Group) and 20 eyes with suspicious preoperative Placido-based corneal topography that underwent LASIK and are stable with 3 years of postoperative follow-up (Control Stable group). The following metrics were evaluated: age, preoperative central corneal thickness (CCT), residual stromal bed (RSB), ectasia risk score system scores, and percent tissue altered PTA, derived from [PTA = (FT +AD)/CCT] where FT = flap thickness, AD = ablation depth, and CCT = preoperative central corneal thickness.
Results
Mean values of PTA (36.9 ± 6.1 vs 31.8 ± 4.1, p = 0.0003) and RSB (333.7 ± 45.1 vs 367.3 ± 24.9, p = 0.002) were significantly different between ectasia and stable control groups respectively. Mean values of CCT (528.7 ± 34.9 vs. 537.8 ± 19.7, p = 0.197) and Age 34.6 ± 9.0 vs. 34.5 ± 11.5; p = 0.964) were not significantly different between the groups Stepwise logistic regression revealed the PTA as the single most significant independent variable (P < 0.0001) identifying ectasia risk.
Conclusion
This aggregate analysis provides evidence that Percent Tissue Altered (PTA) at the time of LASIK was significantly associated with the development of ectasia in eyes with suspicious preoperative topography and was a more robust indicator of risk than all other variables in this patient population.