Effects of pterygium on corneal spherical power and astigmatism

Objective: To evaluate prospectively the corneal refractive status before a nd 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 remo val surgery. Main Outcome Measures: corneal spherical power, astigmatism, surface regula rity index (SRI), and surface asymmetry index (SAI) before and after surger y, and the preoperative pterygium size. Results: Before surgery, pterygium size significantly correlated with spher ical power (Pearson's correlation coefficient, r = -0.370, P < 0.001), asti gmatism (r = 0.600,P < 0.001), SRI (r = 0.367, P < 0.001), and SAI (r = 3.3 87, P < 0.001). The surgery significantly increased spherical power of the cornea, whereas astigmatism, SRI, and SAI were significantly decreased by t he 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 c orrelated with the preoperative pterygium size. Precise prediction of the m agnitude of refractive changes based on the preoperative pterygium size was difficult. Conclusions: The presence of pterygium and its removal significantly influe nce the corneal refraction including spherical power, astigmatism, asymmetr y, and irregularity, with the larger pterygium exerting the greater influen ce. Ophthalmology 2000;107:1568-1571 (C) 2000 by the American Academy of Op hthalmology.