Comparison of methods to measure corneal power for intraocular lens power calculation using a rotating Scheimpflug camera

J Cataract Refract Surg. 2013 Apr;39(4):598-604. doi: 10.1016/j.jcrs.2012.11.022. Epub 2013 Feb 9.


Purpose: To assess the accuracy of corneal power measurements provided by a Scheimpflug camera (Pentacam HR) for intraocular lens (IOL) power calculation in unoperated eyes and compare the results with those of simulated keratometry (SimK) performed with a Placido-disk corneal topographer (Keratron).

Setting: Private practice.

Design: Evaluation of diagnostic test.

Methods: Eight Scheimpflug camera corneal power measurements were analyzed: (1) average K, (2) true net power calculated using the Gaussian optics formula, (3) total corneal refractive power at 2.0 mm calculated by ray tracing on a ring and (4) as the average of the zone inside the ring, (5) total corneal refractive power at 3.0 mm on a ring and (6) as the average of the zone inside the ring, (7) the equivalent K reading at 3.0 mm and (8) at 4.5 mm. The IOL power was calculated using the Hoffer Q, Holladay 1, and SRK/T formulas.

Results: No statistically significant differences were observed between any corneal power measurements, including simulated K, in 41 consecutive patients. The latter showed slightly lower mean absolute errors with all 3 formulas (range 0.26 to 0.27 diopter [D]). The Scheimpflug camera gave the lowest median absolute errors with all formulas; that is, the 3.0 mm equivalent K reading with the Hoffer Q formula (0.18 D) and Holladay 1 formula (0.17 D) and the 2.0 mm total corneal refractive power ring with the SRK/T formula (0.18 D).

Conclusion: Corneal power measurements provided by the Scheimpflug camera and Placido disk corneal topographer displayed comparable accuracy in IOL power calculation.

Publication types

  • Comparative Study
  • Evaluation Study

MeSH terms

  • Aged
  • Cornea / physiology*
  • Corneal Topography
  • Diagnostic Techniques, Ophthalmological*
  • Female
  • Humans
  • Lenses, Intraocular*
  • Male
  • Optics and Photonics*
  • Photography / instrumentation*
  • Prospective Studies
  • Refraction, Ocular / physiology*
  • Reproducibility of Results