Wavefront Aberrations in the Posterior Corneal Surface

Abstract

Purpose: : To measure wavefront aberrations in the posterior corneal surface and to test their contribution to the aberrations in the whole eye.

Methods: : A Scheimpflug photography-based system (the Pentacam) was used to measure corneal aberrations in the right eye for 21 young adults (6 males, 15 females, mean age = 26.1±3.6 yrs). 12 Scheimpflug images along 12 meridians for each measurement were exported from the system and processed to derive corneal heights of the anterior and the posterior corneal surfaces at the 12 meridians. After correcting image distortions caused by both projection and refraction, the anterior and posterior corneal surfaces were reconstructed and 35 Zernike aberrations of the two corneal surfaces were derived through MatLab ray-tracing and Gram-Schmidt procedures.

Results: : For the main Zernike terms, the mean posterior corneal aberrations were 0.034±0.125 (oblique astigmatism, Z₂^-2), 0.276±0.120 (main axis astigmatism, Z₂²), 0.016±0.042 (vertical coma, Z₃^-1), -0.047±0.049 (lateral coma, Z₃¹), and -0.064±0.022 (spherical aberration, Z₄⁰). All main posterior corneal aberrations differed from zero significantly (p<0.025) except of the vertical coma which approached to significance (p= 0.08). The mean Zernike aberrations in the anterior cornea were 0.074±0.421 (Z₂^-2), -0.630±0.592 (Z₂²), -0.066±0.186 (Z₃^-1), -0.051±0.163 (Z₃¹), and 0.211±0.112 (Z₄⁰). The posterior aberrations were 45.5% (Z₂^-2) and 92.2% (Z₃¹) of the anterior corneal aberrations and with the same sign, but 43.9% (Z₂²), 25.1% (Z₃^-1) and 30.2% (Z₄⁰) with the opposite sign.

Keywords: aberrations • cornea: basic science • image processing