Purpose: To assess the changes in corneal curvature indices following pterygium surgery and its correlation with total, triangular(corneal) part, trapezoidal (bulbar conjunctival) part of area of pterygium.

Background: Pterygium, a fibrovascular growth on the ocular surface, frequently induces change in corneal curvature leading to astigmatism. This effect is due to mechanical traction and tear film pooling. (10). This induced astigmatism increases with increase grade of pterygium. (11) It was our observation that in the same grade of pterygium there is substantial variability in corneal curvature changes, which suggests that some other factor which can induce traction on the corneal surface is also responsible for pterygium induced astigmatism. Hypothetically we thought of surface area of pterygium may have effect of mechanical traction the corneal surface. Therefore, this study was conducted to evaluate effect of surface area of anatomical subdivision of pterygium, corneal triangle as well as conjunctival trapezoid to induce corneal astigmatism by measuring this area and co relating with postoperative corneal curvature changes (induced astigmatism) in patients undergoing pterygium excision.

Methods: A cross-sectional, non-interventional study was conducted on 80 patients with primary pterygium. Surface area was calculated using standard geometrical formulas for triangular (corneal) and trapezoidal (bulbar conjunctival) regions. Keratometric readings (K1 and K2) were obtained preoperatively and three months post pterygium surgery. Data were statistically analyzed to assess correlations between both surface area and keratometric changes.

Results: The mean increase in K1 and K2 values showed a statistically significant progressive trend with increasing pterygium grades (p<0.05). However, both total surface area and its anatomical parts demonstrated significant correlations with keratometric increases. Specifically, higher total area, triangular area, and trapezium area were associated with greater postoperative keratometric shifts (p<0.001 in most subgroups).

Conclusion: The extent of change in corneal curvature in pterygium is not only affected by grade of the pterygium but surface area of pterygium its variables as total, corneal triangular and conjunctival trapezoid anatomical subdivisions also play a vital role in inducing astigmatism. Both the triangular and trapezium components contribute significantly to astigmatic refractive changes. Quantitative area of pterygium assessment should complement grading to assess amount of induced astigmatism.