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 astigmatism case 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.    iranian journal of ophthalmology 201224(3):52-56 © 2012 by the iranian society of ophthalmology