Topography-Guided Refractive Astigmatism Outcomes: Predictions Comparing Three Different Programming Methods

Abstract

Purpose: To identify the laser programming strategy that will achieve optimal refractive outcomes of LASIK with a topography-guided laser for eyes with a disparity between cylinder measured by manifest refraction and cylinder measured by topography.

Setting: Six surgeons at 5 clinical sites in the USA.

Design: Retrospective data review.

Methods: Preoperative, treatment, and postoperative data on 52 eyes that underwent topography-guided LASIK with the WaveLight EX500 Contoura® Vision excimer laser ablation profile in which the vectors representing the preoperative refractive cylinder and the cylinder measured by the WaveLight® Topolyzer™ VARIO Diagnostic Device (Vario cylinder) differed by >/= 0.50D and/or >/= 10 degrees of orientation were analyzed retrospectively. Data were contributed by six surgeons using the laser at 5 different clinical sites. Vector analysis of postoperative cylindrical refractive error and the actual laser programming strategy was used to calculate the cylindrical correction that would, theoretically, have completely eliminated postoperative refractive cylinder. This was compared to expected results using the preoperative manifest cylinder, the topographic cylinder, and the Phorcides Analytic Engine (Phorcides LLC, North Oaks MN; Phorcides). For analysis, subjects were stratified on the basis of the vector difference between Manifest and Topo cylinder (High, >0.75 D; and Low, ≤0.75 D).

Results: The poorest calculated theoretical outcomes were obtained with the manifest refraction (centroid: -0.43, 0.22; mean calculated error vector: 0.56 ± 0.42 D; p=ns). Better outcomes were obtained with the topographically measured refraction (centroid: 0.37, 0.02; mean calculated error vector: 0.47 ± 0.33 D; p=ns). The best outcomes were obtained with Phorcides (centroid: -0.15, 0.06; mean calculated error vector: 0.39 ± 0.28 D; p=ns). The mean error vector magnitude in the Phorcides Low group was significantly lower than for the Manifest and Topo Low groups (0.26 D vs 0.48 D and 0.33 D; p<0.01). The mean error magnitude in the Phorcides High group was nearly 0.25 D lower than for the Manifest High group (0.48 D vs 0.70 D; p<0.01), but was the same as for the Topo High group (0.48 D vs 0.48 D).

Conclusion: Our study suggests that using the topographically measured cylinder or the cylinder selected by Phorcides will produce more desirable refractive outcomes than entry of the preoperative refractive cylinder as the basis for correction of myopia and myopic astigmatism with the WaveLight Contoura Vision excimer laser.

Keywords: LASIK; PRK; astigmatism; excimer; laser; topography.

Conflict of interest statement

Drs Durrie, Potvin, Stonecipher, Stulting, and Krueger are consultants to Alcon. Science in Vision (Potvin) received funding for data analysis and manuscript preparation. Dr Lobanoff was the developer of the Phorcides Analytic Engine and has a financial interest in Phorcides, LLC. He is also a paid consultant for Alcon and has a patent pending on the technology behind the Phorcides software. Drs Stulting, Potvin, Krueger, and Stonecipher report grants from Alcon. Dr Daniel S Durrie helped organize the study for Alcon and is a consultant for J&J that has competitive equipment to the Alcon equipment used in the study. Dr Motwani reports grants from Alcon, Inc, outside the submitted work. In addition, Dr Motwani has a patent relating to the use of topographic guided ablation/Contoura for the creation of uniform corneas. The authors report no other conflicts of interest in this work.

© 2020 Stulting et al.

Figures

Figure 1

Treatment planning page for the WaveLight Contoura® Vision laser.

Figure 2

Cumulative uncorrected visual acuities at 3 months.

Figure 3

Change in corrected distance visual acuity from preoperative exam to the 3-month postoperative exam.

Figure 4

Error vectors: difference between calculated Manifest and Best outcomes. Ellipses are the centroid ± SD for the low () and high (- - -) groups.

Figure 5

Error vectors: difference between Topo and Best outcomes. Ellipses are the centroid ± SD for the low () and high (- - -) groups.

Figure 6

Error vectors: difference between Phorcides and Best outcomes. Ellipses are the centroid ± SD for the low () and high (- - -) groups.