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Mohamed Abou Shousha , MD, 1,2 Osama S. Ibrahim, MD, PhD 2

Discrepancy Between Scheimpflug and Placido-Based Topographies and Correlation with Astigmatism After Scheimpflug Topography-Guided LASIK. Mohamed Abou Shousha , MD, 1,2 Osama S. Ibrahim, MD, PhD 2 1. Bascom Palmer Eye Institute, University of Miami, Miller School of Medicine, FL, USA

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Mohamed Abou Shousha , MD, 1,2 Osama S. Ibrahim, MD, PhD 2

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  1. Discrepancy Between Scheimpflug and Placido-Based Topographies and Correlation with Astigmatism After Scheimpflug Topography-Guided LASIK Mohamed AbouShousha, MD,1,2 Osama S. Ibrahim, MD, PhD 2 1.Bascom Palmer Eye Institute, University of Miami, Miller School of Medicine, FL, USA 2. Faculty of Medicine, University of Alexandria, Alexandria , EGYPT The authors have no financial interest in the subject matter of this poster.

  2. Purpose To compare • Keratometry (K) readings • K reading axes • Topographic astigmatism obtained by: Scheimpflug- based topographer & Placido-based topographer Then correlating presence of discrepancies to: postoperative astigmatism after Scheimpflug topography-guided LASIK

  3. Methods Retrospective non-randomized study 40 eyes of 20 patients who underwent Scheimpflug topography-guided LASIK (Oculink) for the correction of primary ametropia. • Scheimpflug (ALLEGRO Oculyzer) and Placido-based (ALLEGRO Topolyzer) • topographies were obtained. • Adjusting the head position to avoid head tilt was done in all measures. • K readings, their axes and topographic astigmatism obtained from the two topographers were compared • Presence of discrepancy was correlated to postoperative astigmatism after Scheimpflug topography-guided LASIK (Oculink).

  4. Results: K readings • In 50% of eyes (n=20), the two topographers showed more than 0.5 Diopter (D) difference in K readings, while in 5% of eyes (n=2) the difference was more than 1 D. • In 95% of those eyes (n=19), the K readings obtained from the Scheimpflug topographer were steeper.

  5. Difference in AvgK is 1.2 D, Steeper by Scheimpflug topographer Difference in K astigmatism is 0.8 D, more astigmatism by Scheimpflug topographer Placido-based topographer Scheimpflug- based topographer Avg K: 42.1 D Astigmatism: -3 D Axis: 23.8 Avg K 43.3 D Astigmatism: -3.8 D Axis: 16.8

  6. Results: Topographic astigmatism • In 15% of eyes (n=6), there was more than 0.5 D difference in topographic astigmatism between the two topographers. • In 67% of those eyes (n=4) it was more in the Scheimpflug topographer.

  7. Difference in K astigmatism is 0.8 D more astigmatism by Scheimpflug topographer Placido-based topographer Scheimpflug- based topographer Avg K: 44.7 D Astigmatism: -0.4 D Axis: 2.8 Avg K: 44.9 D Astigmatism: -1.2 D Axis: 179.6

  8. Results: K readings axes • In 12.5% of eyes (n=5), there was more than 10 degrees difference • In 7.5% of eyes (n=3) there was more than 20 degrees difference in K readings axes.

  9. Difference in Axes is 10.5 Difference in Avg K is 0.1 D Difference in K astigmatism is 0.2 D Scheimpflug- based topographer Placido-based topographer AvgK: 42.2 D Astigmatism: -2.8D Axis: 178 AvgK: 42.3 D Astigmatism: -3 D Axis: 168.5

  10. Difference in Axes is 22.3 Difference in Avg K is 0.1 D Difference in K astigmatism is 0.3 D Scheimpflug- based topographer Placido-based topographer Avg K: 42.1 D K astigmatism: -0.3 D Axis 164.4 Avg K: 42.9 D Astigmatism: -0.6 D Axis: 6.7

  11. Results: Scheimpflug topography-guided LASIK (Oculink) • Postoperative astigmatism of more than 1 D was present in 30% of eyes (n=12). • 75% of those eyes (n=9) showed discrepancies between the two topographers with regard K readings, their axes and/or topographic astigmatism.

  12. Conclusion: • Discrepancies exist between Scheimpflug and Placido based topographers with regard K readings, their axes and topographic astigmatism. • Cases that showed discrepancies had a higher incidence of postoperative astigmatism after Scheimpflug topography-guided LASIK.

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