Eyeworld

JUN 2017

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

Issue link: https://digital.eyeworld.org/i/831102

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8 EW ASCRS NEWS June 2017 Dr. Koch noted that even in normal corneas, errors in estimating total corneal power can be as high as 0.5 D due to variations in the poste- rior to anterior ratio. "Then you have corneas for which this extrapolation creates much larger errors—atypical cor- neas, after refractive surgery, after keratoplasty, ectasia, and the use of toric IOLs," Dr. Koch said. Two ways to accurately measure the posterior cornea are tomogra- phy and the Cassini (i-Optics, The Hague, the Netherlands). Tomogra- phy—using Scheimpflug technology and OCT devices—measures the pos- terior cornea on an elevation-based method. Direct measurement of the second Purkinje is done with a Cas- sini, which uses color light-emitting diodes for anterior corneal curvature and white LEDs to measure posterior curvature. Dr. Koch's research comparing posterior corneal power with earlier software versions of the Galilei and the Cassini show a large range in corneal power among post-LASIK and post-PRK corneas. "We have to do better," Dr. Koch said. Companies are aware and making progress. Formulas' role The posterior cornea is difficult to measure because of the small differ- ence in the refractive index between the cornea and aqueous. Another Inaugural continued from page 3 Steinert Refractive Lecture at Refractive Day

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