FEB 05, 2019
Investigators compared refractive outcomes of topography-guided LASIK treatment based on anterior corneal astigmatism (ACA) versus manifest refractive astigmatism.
This retrospective analysis included 1,274 consecutive eyes with primary myopic astigmatism that underwent LASIK; 905 eyes had manifest refractive astigmatism axis treatments and 369 had Wavelight Contoura-measured ACA axis treatments (Alcon). The cohort was divided into those with a discrepancy of 5° to 20° (small-angle group) or 21° and 45° (large-angle group)
In the small-angle discrepancy group, the efficacy index of eyes treated on the refractive astigmatism and ACA axes were similar (0.98 vs. 0.97; P=0.84).
In the large-angle discrepancy group, the postoperative unilateral UDVA within the refractive astigmatism-treated group was superior compared with the ACA-treated group, resulting in a lower efficacy index and 15.3% more eyes that had a worse postop UDVA by 1 or more lines than preoperative CDVA. Refractive astigmatism results and cylinder vector analyses were also superior in the manifest refraction axis treatments, especially when the discrepancy in the axis was large.
Eyes with naturally occurring irregular astigmatism and asymmetrical topographies on keratometric maps were not excluded
Though there is a small benefit in eyes treated based on the refractive astigmatism axis; the efficacy, accuracy and safety of topographic axis treatment is comparable when the axis discrepancy is between 5° and 20°. However, in eyes where the axis discrepancy was between 21° and 45°, topographic axis treatments showed statistically significant inferior outcomes, and a greater excimer laser retreatment rate.
These findings suggest that the measurement of exclusively anterior corneal astigmatism is not sufficient for refractive surgical procedures, confirming the role of other components of the optical system such as posterior corneal astigmatism. Though in cataract surgery there is 1 less variable of lenticular astigmatism, these findings can also be extrapolated to toric IOL positioning by considering a manifest refraction axis placement.