Effects of pterygium on corneal spherical power and astigmatism.

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.