Analysis of the relationship between the size of pterygium and induced corneal astigmatism

Objective To study the relationship between pterygium size(extension,width,total area) and corneal astigmatism in eyes with unilateral primary pterygium.Also to determine the critical size for before the occurrence of a significant corneal astigmatism.Methods This study was conducted on 112 eyes of 112 patients with unilateral primary pterygium.The extension and width were measured and the total area was calculated.Automated keratometry and OrbscanⅡ(3 mm zone) was used to determine corneal astigmatism.Results The extension of pterygium ranged from 0.38 to 5.69 mm(mean,2.15±1.12 mm),the width ranged from 1.35 to 8.26 mm(mean,3.27±1.20 mm)and the total area ranged from 1.8 to 20.5 mm2(mean,6.6±4.1 mm2).The mean value of corneal astigmatism was significantly higher in pterygium-affected eyes(3.2±1.9 D) than control eyes(0.26±0.5 D).With-the-rule was the main type of pterygium-induced astigmatism(59.2%),followed by against-the-rule(30.6%) and oblique(10.2%).Pterygium extension had the best correlation followed by total area and width.A stronger correlation was noted between pterygium size and the difference in corneal astigmatism between pterygium-affected eyes and control eyes.Pterygium Induced 2.5±0.9 D of corneal astigmatism when its extension exceeded 2.0±0.3 mm,width exceeded 5.0±0.2 mm,or total vational study performed on patients with unilateral primary area exceeded(6.25±1.9) mm2.Conclusion Pterygium extension and total area have a stronger correlation with corneal astigmatism than with width.Surgical intervention is indicated when pterygium extension exceeded 2.0±0.3 mm,width exceeded 5.0±0.2 mm,or total area exceeded(6.25±1.9) mm2.