Comparison of Surgically-induced Astigmatism using Topography and Keratometry in Patients undergoing Phacoemulsification and Small Incision Cataract Surgery: A Prospective Interventional Study

Abstract

Introduction: Topographic measurement of corneal astigmatism is the current standard of care because, in addition to measuring corneal astigmatism, it identifies irregular astigmatism, which may limit optimum surgical results. The present study focuses on the use of topography to measure Surgically Induced Astigmatism (SIA), which is not a routine practice in most institutions, and compares it with keratometry values of corneal astigmatism. The present study highlights the accuracy of topography in the measurement of astigmatism, with its additional benefits being the measurement of irregular astigmatism and assessment of tear film status. Aim: To compare SIA using topography and keratometry in patients undergoing phacoemulsification and Small Incision Cataract Surgery (SICS). Materials and Methods: The present study was a prospective, interventional study conducted in the Ophthalmology Department of Bharti Vidyapeeth (deemed to be University) Medical College and Hospital, Sangli, Maharashtra, India for 18 months (November 2019 to April 2021). A total of 100 cases (100 eyes) with cataracts were randomly divided into Group-A (n=50) and Group-B (n=50), respectively, underwent Phacoemulsification and SICS. Before the surgery, the astigmatism of each patient was noted by both topography and keratometry. On the 45th postoperative day, patients’ Uncorrected Visual Acuity (UCVA), Best Corrected Visual Acuity (BCVA), automated keratometry readings, and corneal topography readings were taken, based on which SIA was calculated by SIA calculator version 2.0. The mean SIA in both groups was calculated and compared. An unpaired t-test was used to compare the mean of different variables in the two groups, Group-A and Group-B. A p-value of <0.05 was considered statistically significant. Results: The majority of cases were in the age group of 61- 70 years, with 23 (46%) cases in Group-A and 27 (54%) in Group-B. In the study, the mean SIA by keratometry in Group-A was 0.43±0.02D and in Group-B was 1.24±0.04D (p<0.0001), and the mean SIA by topography in Group-A was 0.49±0.02D and in Group-B was 1.28±0.03D (p<0.0001), indicating that phacoemulsification causes less SIA compared to SICS. Upon comparing the mean SIA calculated by keratometry and topography in both study groups, it was found that p<0.02 in Group-A and p<0.4 in Group-B, suggesting that both p-values are not significant. This indicates that both keratometry and topography will give similar results and can be used for determining SIA. Conclusion: The study showed that phacoemulsification produces less mean SIA compared to SICS, leading to better visual outcomes and early visual rehabilitation in contrast to the SICS group. The present study also concluded that both keratometry and corneal topography can be used for the calculation of SIA as both give similar results, although topography remains an important tool in the calculation of Intraocular Lens (IOL) power in patients with corneal pathologies and post-refractive surgeries.