Discrepancy Between Scheimpflug and Placido-Based Topographies
and Correlation with Astigmatism After
Scheimpflug Topography-Guided LASIK
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, USA2. Faculty of Medicine, University of Alexandria, Alexandria , EGYPT
The authors have no financial interest in the subject matter of this poster.
PurposePurpose
To compare
Keratometry (K) readings K reading axes Topographic astigmatism
Scheimpflug- based topographer
Then correlating presence of discrepancies to: postoperative astigmatism after Scheimpflug topography-guided LASIK
Placido-based topographer
obtained by:
&
MethodsMethods
Retrospective non-randomized study 40 eyes of 20 patients who underwent
Scheimpflug topography-guided LASIK (Oculink) for the correction of primary ametropia.
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).
Scheimpflug (ALLEGRO Oculyzer) and Placido-based (ALLEGRO Topolyzer) topographies were obtained.
Adjusting the head position to avoid head tilt was done in all measures.
Results: K readingsResults: 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.
Avg K: 42.1 DAstigmatism: -3 D
Axis: 23.8
Avg K: 42.1 DAstigmatism: -3 D
Axis: 23.8
Avg K 43.3 DAstigmatism: -3.8 D
Axis: 16.8
Avg K 43.3 DAstigmatism: -3.8 D
Axis: 16.8
Difference in Avg K is 1.2 D, Steeper by Scheimpflug topographer
Difference in K astigmatism is 0.8 D, more astigmatism by Scheimpflug topographer
Difference in Avg K is 1.2 D, Steeper by Scheimpflug topographer
Difference in K astigmatism is 0.8 D, more astigmatism by Scheimpflug topographer
Placido-based topographerPlacido-based topographer Scheimpflug- based topographerScheimpflug- based topographer
Results: Topographic astigmatism 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.
Avg K: 44.7 DAstigmatism: -0.4 D
Axis: 2.8
Avg K: 44.7 DAstigmatism: -0.4 D
Axis: 2.8
Avg K: 44.9 DAstigmatism: -1.2 D
Axis: 179.6
Avg K: 44.9 DAstigmatism: -1.2 D
Axis: 179.6
Difference in K astigmatism is 0.8 Dmore astigmatism by Scheimpflug topographer
Difference in K astigmatism is 0.8 Dmore astigmatism by Scheimpflug topographer
Placido-based topographerPlacido-based topographer Scheimpflug- based topographerScheimpflug- based topographer
Results: K readings axesResults: 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.
Avg K: 42.2 DAstigmatism: -2.8D
Axis: 178
Avg K: 42.2 DAstigmatism: -2.8D
Axis: 178
Avg K: 42.3 DAstigmatism: -3 D
Axis: 168.5
Avg K: 42.3 DAstigmatism: -3 D
Axis: 168.5
Placido-based topographerPlacido-based topographer Scheimpflug- based topographerScheimpflug- based topographer
Difference in Axes is 10.5
Difference in Avg K is 0.1 DDifference in K astigmatism is 0.2 D
Difference in Axes is 10.5
Difference in Avg K is 0.1 DDifference in K astigmatism is 0.2 D
Avg K: 42.1 DK astigmatism: -0.3 D
Axis 164.4
Avg K: 42.1 DK astigmatism: -0.3 D
Axis 164.4
Avg K: 42.9 DAstigmatism: -0.6 D
Axis: 6.7
Avg K: 42.9 DAstigmatism: -0.6 D
Axis: 6.7
Placido-based topographerPlacido-based topographer Scheimpflug- based topographerScheimpflug- based topographer
Difference in Axes is 22.3
Difference in Avg K is 0.1 DDifference in K astigmatism is 0.3 D
Difference in Axes is 22.3
Difference in Avg K is 0.1 DDifference in K astigmatism is 0.3 D
Results: Scheimpflug topography-guided LASIK (Oculink)
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.