Pterygium Induced Astigmatism Before and After Surgery

INTRODUCTION: Pterygium is a triangular encroachment of the bulbar conjunctiva onto the cornea, a clinical picture recognized from ancient times. It occurs in two forms. A true pterygium is a degenerative and hyperplastic process in which conjunctiva actively invades the cornea. A pseudopterygium is the result of an inflammatory process. When Pterygium remains small, it gives rise to no symptoms, apart from slight irritation in the periods of inflammatory engorgement. The progression of a pterygium onto the cornea can lead to both significant corneal distortion and the development of large amounts of corneal astigmatism. OBJECTIVES: 1. To find out type of corneal astigmatism produced by pterygium. 2. To find out changes in corneal astigmatism after surgery. 3. To determine the difference in mean corneal curvatures before and after pterygium excision. METHODOLOGY: This randomized prospective study was conducted at Coimbatore medical college Hospital, Coimbatore from September 2010 to August 2011. Forty four patients with primary pterygium underwent pterygium excision with conjunctival autograft or simple closure of conjunctiva. Type of surgical procedure selected randomly after estimating grade of pterygium with the help of slit lamp, astigmatism, corneal curvature by manual keratometer, auto refractometer and auto keratometer. The mean and standard deviation were calculated for the corneal curvatures and astigmatism before and after the surgery. Paired sample t-test wasused to compare the corneal curvatures and power of cylinder induced before and after pterygium excision. P-value<0.05 was considered significant. RESULTS: Pre operatively, 81.8% of the patient in conjunctival auto graft group and 68% of patients in pterygium excision with simple closure group had ‘with the rule astigmatism’. In conjunctival auto graft surgery, the preoperative cylindrical error decreased from 3.2± 2.4 D to 1.98 ±1D postoperatively (P<.018). Before surgery, the keratometry readings were 42.15 ± 1.94D in horizontal meridian and 44.55± 1.62 D in vertical meridian. Postoperatively, these values were 44.41±1.4D in horizontal meridian and 46.43 ± 1.8 D in vertical meridian. (p<.000) In simple closure surgery, the preoperative cylindrical error decreased from 2.8± 2.0 D to 1.5 ±1D postoperatively in simple closure surgery (p<.010). The keratometry readings were 44.86 ± 2.74 D in horizontal meridian and 47.14±2.91 D in vertical meridian. Postoperatively, these values were 44.55±0.85 D in horizontal meridian and 46.05 ± 2.4 D in vertical meridian (p < .015). CONCLUSION: Pterygium mostly induces ‘with the rule astigmatism’. Pterygium excision brings a statistically significant change in corneal curvatures, which leads to a decrease in cylindrical correction