Effect of On-Axis Incision on Surgically Induced Astigmatism Following Phacoemulsification Cataract Surgery.

OBJECTIVE: To estimate surgically induced astigmatism (SIA) and the flattening effect produced by an on-axis incision in patients undergoing phacoemulsification cataract surgery. STUDY DESIGN: A quasi-experimental study. Place and Duration of the Study: Department of Eye, Combined Military Hospital, Lahore, Pakistan, from May to September 2024. METHODOLOGY: A total of 142 eyes underwent phacoemulsification with a 2.75-mm limbal incision placed on the steep axis. Keratometric (K) readings, including flat K (K1) and its axis, steep K (K2) and its axis, and astigmatism and its axis, were measured by the same technician before surgery and again 6 weeks postoperatively using an optical biometer (Tomey AL 100). Uncorrected visual acuity (UCVA) and corrected distance visual acuity (CDVA) were recorded for all patients preoperatively and postoperatively. SIA was calculated using the ASSORT online calculator, and changes in astigmatism, UCVA, and CDVA were analysed using the Wilcoxon signed-rank test (SPSS version 26), with statistical significance set at p < 0.05. RESULTS: The mean age of participants was 62.9 ± 6.9 years, with 60.6% males. Preoperative astigmatism averaged 0.88 ± 0.52 dioptres (D) and decreased to 0.65 ± 0.48 D postoperatively, representing a mean reduction of 0.23 ± 0.30 D (p < 0.001). The mean SIA was 0.58 ± 0.50 D, and target-induced astigmatism was 0.45 ± 0.45 D. Both UCVA and CDVA improved significantly (p <0.001). Nearly 70% of eyes gained three or more Snellen lines of corrected vision. CONCLUSION: A 2.75-mm on-axis limbal incision during phacoemulsification produces low and predictable SIA, a statistically significant reduction in corneal astigmatism and substantial improvement in visual acuity. This approach provides a practical, cost-neutral option for astigmatism management in cataract surgery. KEY WORDS: Phacoemulsification, Astigmatism, Cataract extraction, Cornea/surgery, Visual acuity.