Statistical Analysis of Factors Affecting Surgically Induced Astigmatism Following Trabeculectomy

PURPOSE: To objectively evaluate surgically induced astigmatism (SIA) after trabeculectomy with mitomycin C and investigate the relationships between SIA and various factors. PATIENTS AND METHODS: This retrospective study included the right eyes of 66 consecutive patients who underwent standard trabeculectomy performed in the superior temporal quadrant for the first time by a single surgeon. Keratometry recordings made before surgery and 3 months after surgery were collected to calculate the SIA in each patient. The arithmetic mean of SIA (M-SIA) and the centroid of SIA (C-SIA) were determined using vector analysis. The relationships between the magnitude of SIA and the following possible related factors were assessed: age, sex, pre-operative corneal astigmatism, pre-operative intraocular pressure (IOP), 3-month postoperative IOP, pre-operative best-corrected visual acuity (BCVA), 3-month postoperative BCVA, the number of total scleral flap sutures (T-SFS), the number of leftover scleral flap sutures without laser suture lysis at 3 months postoperatively (L-SFS), shape of the scleral flap (triangle or trapezoid), and incision type of the conjunctival flap (fornix- or limbal-based). RESULTS: The mean (± standard deviation) M-SIA was 1.00 ± 0.85 D, and the mean C-SIA was 0.34 ± 1.28 D at 104°. The direction of C-SIA showed a trend of corneal steepening to the superior temporal location, in the direction of the scleral flap location. There were significant correlations of the magnitudes of SIA with the number of T-SFS (P = 0.001) and the number of L-SFS (P < 0.001). CONCLUSION: Trabeculectomy induced SIA in the direction of the scleral flap location, and scleral sutures are significantly associated with the SIA. The scleral suture may play a key role in steepening the cornea toward the scleral flap direction in post-trabeculectomy patients.