Induced Secondary Astigmatism and Horizontal Coma after LASIK for Mixed Astigmatism

Purpose : To describe a distinctive pattern of induced higher order aberration (HOA) after LASIK for mixed astigmatismCase reports : Wavefront-guided LASIK with iris recognition and eye tracking (Excimer laser: Technolas 217z; APT protocol; Microkeratome: Moria CB) was performed in six eyes with moderate to high mixed astigmatism for a nominal optical zone of 6.3 mm. The patients were re-examined beyond 9 months postoperatively.Results : Postoperative uncorrected distance visual acuities (UDVA) equaled preoperative corrected distance visual acuities (CDVA). The cycloplegic cylinder increased an average of about 2.50 D compared with dry retinoscopy. Significant increases in HOAs were detected with pupils dilated, specially in the amounts of secondary astigmatism (mean change=0.41 µm) and horizontal coma (HC) (mean change=0.29 µm). Large kappa angles were detected in all of the eyes studied (mean=7.45̊).Conclusion : The bitoric ablation profile of mixed astigmatism LASIK may induce significant secondary astigmatism which causes a remarkable disparity between dry and wet refraction and manifests as an unusual skiascopic reflex during wet retinoscopy. A large kappa angle may cause tilted ablation and induce HC