J Med Assoc Thai 2003; 86 (1):16

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The Effect of Pterygium on Corneal Astigmatism
Kampitak K Mail

Objective
: To determine the effect of pterygium on corneal astigmatism.
Method
: Two hundred and forty three eyes of 173 patients with primary pterygium were
included in the present study. The extension of pterygium was measured by slit lamp and corneal
astigmatism was measured by corneal topography. Correlation of the data was discussed.
Results
: The size of pterygium extended from 0.50 mm to 8.10 mm (2.11
เธ‘
1.10). The diopter
of corneal astigmatism ranged from 0.10 diopter to 14.60 diopter ( 1.86
เธ‘
2.39). The axis of corneal
astigmatism was found in vertical axis 156 eyes (64.2% ), oblique axis 36 eyes ( 14.8%) and horizontal
axis 51 eyes (21.0% ). The degree of corneal astigmatism significantly correlated with the extension
of pterygium on the cornea (R Square= 0.45, p
<
0.001). When the extension of pterygium exceeded
2.25 mm, there was a chance of developing corneal astigmatism of 2 diopter or more (86.21% of
sensitivity and 80% of specificity).
Conclusion
: The extension of pterygium is significantly correlated with the degree of cor-
neal astigmatism in the positive direction, with the highest percentage of with-the-rule astigmatism.
Pterygium exceeding 2.25 mm of length should be considered within the limits of surgery.
Key word
: Pterygium, Corneal Astigmatism

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