A Comparative Study of Surgically Induced Astigmatism in Straight, Frown and Modified Chevron Incisions in Manual Small Incision Cataract Surgery

Abstract

PURPOSE:To compare the surgically induced astigmatism following straight, frown and modified chevron incisions in MSICS. METHOD: This is a Prospective interventional study conducted in RIO Bhopal during academic session of April 2009 to October 2010 in which 145 eyes of 137 patients were evaluated. Patients with relatively soft nuclei and healthy cornea, adequate anterior chamber and those who could be called up for regular follow up were chosen for the study. Preoperative keratometry was done to determine K-reading in both horizontal and vertical meridians. Astigmatism was graded and classified according to Holmström's gradation 1 37.9% cases were given straight incision, 18.6% cases were given Frown incision. While in the remaining 43.4% cases Modified chevron was made. In majority of cases 71%, 6.5 mm incision was made while larger incision 7mm and 7.5mm were made in 23.4% and 5.5% cases respectively. Post-operative keratometry readings were taken at first post-operative day and at the end of 6 th week following surgery and surgically induced astigmatism was calculated. RESULTS: Post operatively frown incision group's average SIA was 0.68 D. Modified chevron incision group had 1.02 D SIA, Straight incision group had the maximum SIA of 1.15D. However the mean surgically induced astigmatism in all incision types in our study was found to have SIA=1.01 D. CONCLUSION: In our study we observed that Frown incision was the best of all incision types with regards to SIA. KEYWORDS: SIA, Modified chevron incision, straight incision, frown incision. INTRODUCTION:In the developing countries where cost 1 is a major issue, MSICS was developed after the advent of phacoemulsification, and hence it is a relatively younger technique than the latter. Innumerable variations in methodologies of MSICS as well as the utility of MSICS in the day to day practice invoke a great deal of discussion and debate. In MSICS which is based on the concept of scleral tunnel, everything about the wound has to be carefully planned depending on the type of technique, hardness of the nucleus, amount of preoperative astigmatism. 2,3 It has been unequivocally demonstrated that smaller the incision, 4,5 lesser the number of sutures 6,7 and valvular construction of wound would induce minimal corneal curvature change that is astigmatism. The parameters 8 important for the structural integrity of the tunnel are- The self-sealing property of the tunnel.  The location of the wound on the sclera with respect to the limbus, 7,9 and  The shape of the incision. 7,10 Cataract surgery has gone beyond just being a means to get the lens out of the eye. Postoperative astigmatism plays an important role in evaluation of final outcome of surgery. Astigmatic consideration hence forms an integral part of incisional considerations prior to surgery.