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The contribution of the posterior corneal surface to total corneal astigmatism

Session Details

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     

Abstract Details

Purpose:

To evaluate the contribution of the posterior corneal surface to total corneal astigmatism.

Setting:

SynsLaser clinic, Tromsų, Norway

Methods:

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.

Results:

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).

Conclusions:

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.

Financial Interest:

NONE