Comparison of different topographers and keratometers for the purpose of IOL calculation after LASIK

Session Details

Session Title: Pseudophakic IOLs: Depth of Focus. Cataract Surgery Equipment

Session Date/Time: Monday 07/09/2015 | 16:30-18:30

Paper Time: 18:08

Venue: Room 16

First Author: : L.Zumhagen GERMANY

Co Author(s): :    P. Hoffmann   M. Abraham   A. Kotouza   P. Preussner           

Abstract Details

Purpose:

IOL calculation after LASIK is still a challenge. Raytracing software can potentially deliver good results but is dependent on the input data. We evaluated calculation quality with different topographers and keratometers.

Setting:

Augen- und Laserklinik Castrop-Rauxel, Deutschland / Germany

Methods:

We evaluated 13 IOL calculations after myopic/astigmatic LASIK or PRK. Biometry was carried out with the Haag-Streit Lenstar and Zeiss IOLMaster V5. Topographic data was generated with the Oculus Pentacam Hires, Tomey TMS-5 and Ziemer Galilei G-6 and imported into the Raytracing software Okulix 8.93. The difference between manifest refraction after surgery and predicted refraction (prediction error) was analyzed. Outliers were defined as an absolute prediction error ≥ 1 D.

Results:

Prediction error of raytracing power calculation was –0.40 ± 0.60 D (3 outliers) for the Pentacam, +0.28 ± 0.68 D (1 outlier) for the TMS-5 and +0.09 ± 0.75 D (2 outliers) for the Galilei. IOLMaster with Haigis-L algorithm yielded –0.84 ± 0.80 D (6 outliers), Lenstar with Shammas algorithm –0.42 ± 1.01 D (4 outliers). Raytracing with averaging all three topographers yielded –0.06 ± 0.60 D (1 outlier).

Conclusions:

Considerable differences between topographic data sets do exist and lead to different results in raytracing IOL calculation. While those differences seem to be quite small in normal corneae, they seem to enlarge in post LASIK cornea. Averaging all three topographers yields surprisingly good results. Tweaking keratometric radii like the Haigis-L or Shammas algorithm yields considerably higher unsystematic errors. Topographic data quality is of paramount importance. Great care must be taken in eyes with eccentric ablations as the numeric IOL power calculation may be very wrong. A visual check of the simulated retinal image is helpful in these tough cases.

Financial Interest:

One of the authors gains financially from product or procedure presented