FEB 26, 2018
This retrospective study compared vector planning to manifest refraction planning in patients undergoing LASIK for myopic astigmatism.
The study included 85 treatments based on manifest astigmatism and 79 treatments based on vector planning, which incorporates both manifest refraction and corneal topographic shape. All patients received LASIK with an aberration-neutral profile centered on the visual axis considering 70% of the pupil offset toward the corneal vortex. The treatments used were based 60% emphasis on refractive astigmatism and 40% emphasis on corneal astigmatism.
Only patients with a preoperative ocular residual astigmatism (ORA) of greater than 0.75 D were included. The ORA is defined by the vector difference between the manifest and corneal astigmatism.
Overall, there were no significant differences in postoperative refractive astigmatism, corrected distance visual acuity or uncorrected distance visual acuity between the groups.
The 6-month postoperative mean spherical equivalent favored the vector group, although the minimum level of detection versus the absolute differences in the mean suggested inadequate sample size to confirm these findings. Postoperative ORA and corneal toricity also favored the vector group.
There were no differences in target-induced astigmatism and achieved surgically induced astigmatism, correction index or HOAs (higher order aberrations).
Patients were required to have normal keratometry reading and topography, so this may have limited applicability to cases with the highest ORA.
Performing LASIK for myopic astigmatism with the vector planning approach yielded comparable visual outcomes as manifest refraction planning.