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Effects of pterygium on corneal spherical power and astigmatism
A Tomidokoro1, K Miyata, Y Sakaguchi
1Department of Ophthalmology, Omiya Red Cross Hospital, Saitama, Japan. Miyata Eye Hospital, Miyazaki, Japan. tomidokoro@mse.biglope.ne.jp
Objective:
To evaluate prospectively the corneal refractive status before and after pterygium surgery and its relationship with preoperative pterygium size.
Design:
Prospective, nonrandomized, comparative (self-controlled) trial.
Participants:
One hundred thirty-six eyes undergoing primary pterygium removal surgery.
Main Outcome Measures:
Corneal spherical power, astigmatism, surface regularity index (SRI), and surface asymmetry index (SAI) before and after surgery, and the preoperative pterygium size.
Results:
Before surgery, pterygium size significantly correlated with spherical power (Pearson's correlation coefficient, r = -0.370, P < 0.001), astigmatism (r = 0.600, P < 0.001), SRI (r = 0.367, P < 0.001), and SAI (r = 0.387, P < 0.001). The surgery significantly increased spherical power of the cornea, whereas astigmatism, SRI, and SAI were significantly decreased by the surgery (P < 0.01, paired t test with Bonferroni's correction of P value for multiple comparison). Surgically induced changes in spherical power (r = 0.598, P < 0.001) and astigmatism (r = 0.653, P < 0.001) significantly correlated with the preoperative pterygium size. Precise prediction of the magnitude of refractive changes based on the preoperative pterygium size was difficult.
Conclusions:
The presence of pterygium and its removal significantly influence the corneal refraction including spherical power, astigmatism, asymmetry, and irregularity, with the larger pterygium exerting the greater influence.