Anterior Corneal, Posterior Corneal, and Lenticular Contributions to Ocular Aberrations

Abstract

PURPOSE. To determine the corneal surfaces and lens contributions to ocular aberrations.METHODS. There were 61 healthy participants with ages ranging from 20 to 55 years and refractions À8.25 diopters (D) to þ3.25 D. Anterior and posterior corneal topographies were obtained with an Oculus Pentacam, and ocular aberrations were obtained with an iTrace aberrometer. Raytracing through models of corneas provided total corneal and surface component aberrations for 5-mm-diameter pupils. Lenticular contributions were given as differences between ocular and corneal aberrations. Theoretical raytracing investigated influence of object distance on aberrations.RESULTS. Apart from defocus, the highest aberration coefficients were horizontal astigmatism, horizontal coma, and spherical aberration. Most correlations between lenticular and ocular parameters were positive and significant, with compensation of total corneal aberrations by lenticular aberrations for 5/12 coefficients. Anterior corneal aberrations were approximately three times higher than posterior corneal aberrations and usually had opposite signs. Corneal topographic centers were displaced from aberrometer pupil centers by 0.32 6 0.19 mm nasally and 0.02 6 0.16 mm inferiorly; disregarding corneal decentration relative to pupil center was significant for oblique astigmatism, horizontal coma, and horizontal trefoil. An object at infinity, rather than at the image in the anterior cornea, gave incorrect aberration estimates of the posterior cornea.CONCLUSIONS. Corneal and lenticular aberration magnitudes are similar, and aberrations of the anterior corneal surface are approximately three times those of the posterior surface. Corneal decentration relative to pupil center has significant effects on oblique astigmatism, horizontal coma, and horizontal trefoil. When estimating component aberrations, it is important to use correct object/image conjugates and heights at surfaces.

Variation of axial and oblique astigmatism with accommodation across the visual field

“…We lacked a method for measuring topography of the posterior cornea and therefore included posterior corneal aberrations in our measure of internal astigmatism. This posterior corneal contribution appears to be small, however, according to a recent empirical study (Atchison, Suheimat, Mathur, Lister, & Rozema, 2016) reporting that the posterior cornea compensates less than 5% of anterior corneal lateral astigmatism. That conclusion agrees with our theoretical analysis (Liu & Thibos, in press) indicating the posterior cornea contributes less than 7% to the compensation of the oblique astigmatism of anterior corneal surface.…”

Corneal aberrations after small-incision lenticule extraction versus Q value-guided laser-assisted in situ keratomileusis

“…[25] There are two main sources of wavefront aberrations in human eyes: the cornea and the lens. [26] During the design of the present study, several reasons led us to choose corneal anterior surface aberrations to evaluate the effect of refractive surgery on corneal morphology and visual quality. First, corneal anterior surface aberrations account for nearly 80% of all aberrations of the eye and significantly influence visual quality.…”

Corneal aberrations after small-incision lenticule extraction versus Q-value-guided laser-assisted in situ keratomileusis

“…the cornea and 2.) the lens [13]. In the experimental design stage, several reasons led us to choose corneal anterior surface aberrations to evaluate the effect of refractive surgery on corneal morphology and visual quality: 1.)…”

“…In the experimental design stage, several reasons led us to choose corneal anterior surface aberrations to evaluate the effect of refractive surgery on corneal morphology and visual quality: 1.) corneal anterior surface aberrations accounts for nearly 80% of the total aberration of eye ball and significantly influences visual quality [13,14]; 2.) corneal refractive surgery mainly modifies the corneal anterior surface shape and does not modifies the lens shape; 3.)…”