Repeatability of posterior and total corneal curvature measurements with a dual Scheimpflug-Placido tomographer

J Cataract Refract Surg. 2015 Dec;41(12):2731-8. doi: 10.1016/j.jcrs.2015.07.035.


Purpose: To evaluate the repeatability of the Galilei G4 dual Scheimpflug analyzer in measuring simulated keratometric, total, and posterior corneal curvature in normal and post-refractive surgery eyes.

Setting: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA.

Design: Prospective evaluation of diagnostic technology.

Methods: A single observer performed 3 consecutive measurements in 1 eye of each subject. The following were evaluated in both eyes and in eyes that had previous myopic excimer-laser surgery: (1) simulated keratometric corneal power and astigmatism, (2) total corneal power and astigmatism, and (3) posterior corneal power and astigmatism. Repeatability was assessed by calculating the within-subject standard deviation (Sw), coefficient of variation (CoV), and intra-class correlation coefficient (ICC).

Results: The study evaluated 41 normal eyes and 36 post-refractive surgery eyes. In normal eyes, the Sw was 0.08 diopters (D), 0.10 D, and 0.03 D for simulated keratometric, total, and posterior corneal power, respectively. The CoV ranged from 0.16% to 0.40%, and the ICC was 0.992 or more (P < .001) for all corneal powers. In post-refractive surgery eyes, the Sw was 0.09 D, 0.09 D, and 0.02 D for simulated keratometric, total, and posterior corneal power, respectively. The CoV ranged from 0.19% to 0.32%, and the ICC was 0.990 or more (P < .001) for all corneal powers. For posterior corneal astigmatism, the ICC was 0.814 and 0.886 for normal and post-refractive surgery eyes, respectively.

Conclusions: In normal corneas and corneas that had undergone myopic excimer laser ablation, the dual Scheimpflug analyzer showed high intra-observer repeatability for simulated keratometric, total, and posterior corneal power measurements and moderate repeatability for posterior corneal astigmatism.

Financial disclosure: Drs. Koch, Weikert, and Wang received research support from Ziemer USA, Inc. No other author has a financial or proprietary interest in any material or method mentioned.

Publication types

  • Evaluation Study

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Astigmatism / physiopathology
  • Cornea / pathology*
  • Diagnostic Techniques, Ophthalmological*
  • Female
  • Humans
  • Keratomileusis, Laser In Situ / methods*
  • Lasers, Excimer / therapeutic use*
  • Male
  • Middle Aged
  • Myopia / physiopathology
  • Myopia / surgery*
  • Photography / instrumentation
  • Photorefractive Keratectomy / methods*
  • Prospective Studies
  • Refraction, Ocular / physiology
  • Reproducibility of Results
  • Tomography / instrumentation
  • Visual Acuity / physiology
  • Young Adult