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Accuracy of spherical equivalent using standard keratometry compared to new true keratometry mesasurement using posterior cornea surface curvature

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Session Details

Session Title: Pseudophakic IOL Power Calculation: Photic Phenomena after IOL Implantation

Session Date/Time: Sunday 08/10/2017 | 16:30-18:00

Paper Time: 17:18

Venue: Room 3.4

First Author: : O.Findl AUSTRIA

Co Author(s): :    N. Hirnschall   T. Buehren   M. Trost              

Abstract Details


Standard keratometry does not include measuring the posterior surface of the cornea. Yet research has shown selecting intraocular lenses (IOLs) based on anterior corneal measurements alone may result in refractive surprises due to the negligence of posterior corneal astigmatism. This study compares spherical IOL calculations with traditional keratometry to IOL calculations obtained with True Keratometry (TK), which utilizes both, the anterior and posterior corneal surface to provide total corneal astigmatism.


Hanusch Hospital, Vienna, Austria


Standard keratometry and TK were performed on cataract surgery patients using a swept-source optical coherence tomography-based optical biometer (ZEISS IOLMaster 700, Carl Zeiss Meditec). Patients underwent implantation of the CT ASPHINA 409MP (Carl Zeiss Meditec) and were measured preoperatively as well as 4 weeks postoperatively. Predicted spherical equivalent (SE) was compared between both traditional keratometry and TK utilizing the Haigis; Holladay II and SRK/T formulas. Mean standard keratometry was compared to mean TK.


Mean SE error of 49 eyes of 49 patients was 0.0D +/- 0.46D using the Haigis, 0.0D+/-0.52D using the Holladay, and 0.0+/-0.6 using the SRK/T formula. For TK, the mean SE error was 0.0D +/- 0.46D, 0.0D +/-0.50D, and 0.0D+/-0.58D respectively.The mean absolute error (MAE) for standard keratometry was 0.39D for Haigis, 0.43D for Holladay, and 0.48D for SRK/T. For TK the MAE was 0.37D, 0.42D, and 0.48D respectively. Using standard keratometry, SE error was 0.75D or less in 87.8% of cases for Haigis, 87.8% for Holladay, and 79.6% for SRK/T. Using TK, the values were 87.7%, 89.8%, and 83.7%.


Taking into account the anterior and posterior corneal surface, TK improves IOL outcomes with Haigis, Holladay, and SRK/T formulas compared to use of standard anterior surface keratomety.

Financial Disclosure:

is employed by a forNONEprofit company with an interest in the subject of the presentation, receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented

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