Excimer laser programming of refractive astigmatism vs. anterior corneal astigmatism in the case of ocular residual astigmatism (ORA)

Summary Purpose To determine whether manifest refractive astigmatism (RA) or anterior corneal astigmatism (CA) is the best value for excimer laser programming in cases of ocular residual astigmatism (ORA). Patients and methods Patients who had undergone LASIK surgery with a disagreement between manifest refractive and corneal cylinder (ocular residual astigmatism ORA) > 0.75 D were included retrospectively in this study. We calculated target induced astigmatism vector (TIA), surgically induced astigmatism vector (SIA), difference vector between the astigmatism correction programmed in the excimer laser and refractive astigmatism (DVRA), difference vector between the astigmatism correction programmed in the excimer laser and corneal astigmatism (DVCA) and difference vector between TIA and SIA (DV), by the Alpins method. Vectorial differences between DV and DVRA, and between DV and DVCA, were then calculated to determine whether RA or CA was closest to the ideal cylinder for laser programming. Results Of a total of 104 eyes undergoing LASIK, 22 eyes of 12 patients (21.1%) had an ORA > 0.75 D and were included. Mean ORA was 0.9 ± 0.2 D and mean postoperative subjective cylinder was 0.45 D. The DV-DVRA difference vector was 0.57 ± 0.2 D, and the DV-DVCA difference vector was 0.86 ± 0.4 D (P = 0.02). RA was closer than CA to the ideal astigmatism correction. Conclusion In cases of discrepancy between manifest astigmatism and corneal astigmatism, correction of manifest refractive astigmatism seems to give a better refractive result.