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Session Title: Imaging II
Session Date/Time: Monday 07/10/2013 | 16:30-18:00
Paper Time: 17:32
Venue: Main Lecture Hall (Ground Floor)
First Author: : X.Chen NORWAY
Co Author(s): : A. Stojanovic F. Stojanovic J. Wang T. Paaske Utheim
To evaluate the contribution of the posterior corneal surface to total corneal astigmatism.
SynsLaser clinic, Tromsų, Norway
One hundred and three right eyes of 103 patients were divided into three groups according to the amount of anterior corneal astigmatism within the central 3 mm of the axial power map generated by Scheimpflug topography: low (?1 D, 35 eyes), moderate (1.1 to 2 D, 35 eyes), and high astigmatism group (>2 D, 33 eyes). Total corneal effective power was calculated using ray-tracing. The difference between the anterior and the total corneal astigmatism was calculated using vectorial analysis.
The respective values for mean anterior and total corneal astigmatism were: low, -0.61 ± 0.35 D and -0.47 ± 0.21 D (p= 0.001); moderate, -1.44 ± 0.21 D and -1.13 ± 0.23 D (p=0.000); and high, -2.91 ± 0.71 D and -2.41 ± 0.64 D (p=0.000). Vectorial analysis showed that the difference between the anterior and the total corneal astigmatism was 0.26 ± 0.17 D, 0.45 ± 0.07 D, and 0.55 ± 0.03 D. The differences between the three groups were statistically significant, except between the moderate and high astigmatism groups. The mean posterior corneal astigmatism was 0.22 ± 0.12 D, 0.29 ± 0.02 D, and 0.56 ± 0.27 D (p<0.05). There was a positive correlation between anterior and posterior corneal astigmatism in the 103 eyes (r=0.765, p=0.000).
Posterior corneal surface astigmatism compensates for the anterior corneal astigmatism. It appears that the degree of posterior compensation is proportional to the amount of anterior corneal astigmatism.
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