Korean J Ophthalmol.  2013 Apr;27(2):81-86. 10.3341/kjo.2013.27.2.81.

Changes in Spherical Aberration after Various Corneal Surface Ablation Techniques

Affiliations
  • 1S-Eye Center, Ansan, Korea.
  • 2Kim's Eye Hospital, Seoul, Korea.
  • 3Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea. tikim@yuhs.ac
  • 4Severance Biomedical Science Institute, Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea.

Abstract

PURPOSE
The corneal change induced by refractive procedures influence both the postoperative refractive status and the ocular spherical aberration (SA). We evaluated changes in corneal SA after three types of surface ablation: phototherapeutic keratectomy (PTK), myopic photorefractive keratectomy (PRK), and myopic wavefront-guided laser epithelial keratomileusis (LASEK).
METHODS
Twenty-six eyes (25 patients) were subjected to PTK 26 eyes (14 patients) to PRK, and 34 eyes (17 patients) to wavefront-guided LASEK. Corneal SA was measured with the iTrace in all patients both preoperatively and 6 months postoperatively.
RESULTS
Six months after surgery, mean corneal SA was -0.173 +/- 0.171 micrometer in the PTK group, 0.672 +/- 0.200 micrometer in the PRK group, and 0.143 +/- 0.136 micrometer in the wavefront-guided LASEK group. The mean difference between the preoperative and postoperative corneal SA (DeltaSA) was -0.475 micrometer in the PTK group, 0.402 micrometer in the PRK group, and -0.143 micrometer in the wavefront-guided LASEK group.
CONCLUSIONS
Surgically induced changes in corneal SA vary with procedure. The prediction of the pattern of SA change induced by various surface ablation procedures may be helpful for developing future surgical procedures.

Keyword

Aberration; Laser epithelial keratomileusis; Photorefractive keratectomy; Phototherapeutic keratectomy

MeSH Terms

Adult
Aged
Corneal Dystrophies, Hereditary/*surgery
Corneal Wavefront Aberration/*surgery
Female
Follow-Up Studies
Humans
Keratomileusis, Laser In Situ/*methods
Male
Middle Aged
Myopia/*surgery
Photorefractive Keratectomy/*methods
Prospective Studies
Treatment Outcome

Figure

  • Fig. 1 Distribution of differences between preoperative and postoperative spherical aberration (SA) values (ΔSA). The mean ΔSA of each group is indicated with dotted lines. PRK = photorefractive keratectomy; LASEK = laser epithelial keratomileusis; PTK = phototherapeutic keratectomy.

  • Fig. 2 Output of the iTrace aberrometer showing Zernike coefficients for the corneal wavefronts of patients who underwent three different kinds of surface ablation procedures. (A) A photorefractive keratectomy patient. In this example, Z04 = +0.402 µm, indicating increased corneal spherical aberration. (B) A laser epithelial keratomileusis patient. In this example, Z04 = 0.027 µm, indicating a small amount of corneal spherical aberration; (C) A phototherapeutic keratectomy patient. In this example, Z04 = -0.322 µm, indicating negative spherical aberration. RMS = root mean square; ROC = radius of curvature.


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