Kalanchiarani S, Vinodhini Kannan, Nazeem Farzana Ghouse
BACKGROUND Pterygium is a common degenerative condition seen in the Indian subcontinent. One of the indications for pterygium excision is visual impairment due to astigmatism. Several mechanisms have been suggested to explain the induced astigmatism – a) pooling of the tear film at the leading edge of the pterygium, b) mechanical traction exerted by the pterygium on cornea. Hence this study was done retrospectively to assess the effect of pterygium excision on the induced astigmatism. MATERIALS AND METHODS Records of patients operated for primary ocular pterygium by pterygium excision with primary conjunctival closure/ conjunctival autograft in the age group 18 - 70 years over a 1-year period were analysed retrospectively. Pre-operative and post-operative follow up records of day 1 and 1st month were analysed for changes in corneal curvature and astigmatism using the recorded Automated Refractometry and Keratometry readings. RESULTS Out of the 44 cases analysed retrospectively as 2 groups – pterygium excision with primary conjunctival closure and pterygium excision with conjunctival autograft, majority of them were found to be females (70%), and between 40 - 50 years (90%). Most of the pterygium cases were found to be nasal, and commonly in the right eye and also that the amount of astigmatism increased with the grading of pterygium (p<.000). The most common type of astigmatism noted was “with the rule” astigmatism (75%). The percentage of “against the rule” and oblique astigmatism were 9% & 15% respectively. The decrease in the mean astigmatism after surgery was found to be statistically significant. The difference in t value between the preoperative and one-month postoperative corneal astigmatism was 2.5 D (p<.018). Steepening of both horizontal and vertical meridian was found in conjunctival autograft cases, but in simple closure cases steepening was found only in the vertical meridian. CONCLUSION To conclude, pterygium leads to a considerable effect on corneal refractive status. The common type of astigmatism seen in patients with pterygium is “with-the rule”. There was a positive correlation between the grading of Pterygium and the induced astigmatism. Pterygium surgery effectively decreases this cylindrical error and reverts corneal curvatures towards normality, thus improving subjective visual acuity.
