Ocular Residual Astigmatism, Posterior Corneal Astigmatism, and Anterior Corneal Irregularities in Virgin Eyes Undergoing Topography-guided LASIK

Purpose: To identify the factors that contribute to the arithmetic difference between refractive astigmatism (RA) and anterior corneal astigmatism (ACA), particularly the potential roles of ocular residual astigmatism (ORA), posterior corneal astigmatism (PCA), and anterior corneal irregularities (ACI). Methods: This retrospective study included 360 eyes of 360 consecutive patients undergoing topography-guided LASIK. Preoperative examinations included refraction, topography, and aberrometry. Preoperative corrected distance visual acuity (CDVA) was collected. RA was obtained through manifest refraction. Total corneal astigmatism (TCA), PCA, and ACA were collected from the SIRIUS device (CSO). Patients were grouped into those who met the U.S. Food and Drug Administration (FDA) criteria (FDA+ group) and those who did not (FDA– group) based on the RA–ACA discrepancy. ORA was calculated as the vectorial difference between RA and ACA. ACI was assessed using higher order aberrations and para-central zone astigmatism. Results: Patients were grouped as FDA+ (140 eyes) or FDA– (220 eyes). The FDA+ group exhibited significantly higher RA but lower ORA values than the FDA– group. No significant differences were observed in the corneal astigmatisms (TCA, ACA, PCA) between groups. The ACI difference, assessed by higher order aberrations and paracentral zone astigmatism, was minimal between the two groups. Conclusions: ORA, defined as the vectorial difference between RA and ACA, was the primary contributor to the RA– ACA discrepancy preoperatively, whereas PCA and ACI made minimal contributions.