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.