Disparity between keratometry-style readings and corneal power within the pupil after refractive surgery for myopia

Naoyuki Maeda, Stephen D. Klyce, Michael K. Smolek, Marguerite B. McDonald

Research output: Contribution to journalArticlepeer-review

71 Scopus citations


Purpose. Because keratometry readings may not accurately reflect the refractive changes after keratorefractive surgery for myopia, better methods for the assessment of corneal curvature in the postsurgical cornea are needed. Methods. We developed a procedure to calculate the average central power (ACP) of the cornea within the entrance pupil from videokeratography. Videokeratograph-derived keratometry-style readings (average K; K̄) and calculated ACPs, as well as the differences between the two values, were compared in four groups: normal corneas (n = 30), corneas with regular astigmatism (n = 30), post-radial keratotomy corneas (RK, n = 85), and post- excimer laser photorefractive keratectomy corneas (PRK, n = 63). Intraocular lens (IOL) powers calculated by using K̄ or ACP in the Sanders-Retzlaff- Kraff formula were compared. Results. In the groups with normal corneas or regular astigmatism, none of the eyes showed a difference between K̄ and ACP >0.25 D. However, six (7%) of the RK eyes and 16 (25%) of the PRK eyes had differences >0.55 D; in these eyes, the disparity between IOL powers calculated by using K̄ and IOL powers calculated by using ACP was >0.5 D. Conclusion. These results suggest that basing the calculation of IOL powers on keratometry readings in patients who have undergone RK, PRK, or possibly other refractive procedures may result in a residual refractive error in some eyes. In particular, patients undergoing surgery involving a small optical zone or large attempted correction or both, as well as those with low postoperative keratometry readings, may be at risk for this problem if IOL placement becomes necessary in later years.

Original languageEnglish
Pages (from-to)517-524
Number of pages8
Issue number5
StatePublished - Sep 1997
Externally publishedYes


  • Intraocular lens
  • Keratometry
  • Photorefractive keratectomy
  • Radial keratotomy
  • Videokeratography


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