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.

Conclusion: 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.