Determining spherocylindrical correction using four different wavefront error analysis methods: comparison to manifest refraction

Purpose: To evaluate methods that determine refractive correction from wavefront data that best matches the manifest refraction.

Methods: Wavefront data in the form of Zernike polynomial coefficients from several VISX US Investigational Device Exemption studies were used to calculate the spherocylindrical distance correction using four methods: full pupil second order, central curvature, reduced aperture, and 4-mm pupil. The data were analyzed in two groups, preoperative (3686 measurements, 882 eyes) and 6-month postoperative (2570 measurements, 797 eyes). Differences were formed between values found with each method and the manifest refractive values for the spherical equivalent (dSE), cylinder power (dCc), and axis power (dAc). The wavefront spherical equivalent values were corrected for chromatic shift, lane length, and vertex.

Results: Values derived using the reduced aperture and 4-mm pupil methods corresponded with manifest spherical equivalent values for both preoperative (x(-) = -0.03 diopters [D], x(-) =0.95 D) and postoperative (x(-) = -0.36 D, x =0.65 D) data. The full pupil second order method results corresponded best with manifest data for the astigmatic variables for both preoperative (x(-) dCc=0.15 D, σ dCc=0.31 D, x(-) dAc = 0.02 D, σ dAc =0.22 D) and postoperative data (x dCc=0.25 D, σ dCc=0.33 D, x dAc=0.01 D, σ dAc=0.21 D). However, all methods did well on these variables.

Conclusions: The Zernike coefficient set as measured best calculates the astigmatic correction. The Zernike coefficient set resized to a 4-mm pupil is best in determining spherical equivalent.