Phacotrabeculectomy versus Phaco with Implantation of the Ex-PRESS Device: Surgical and Refractive Outcomes-A Randomized Controlled Trial

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.

Effect of Trabeculectomy on Mean and Centroid Surgically Induced Astigmatism

This study aimed to investigate the arithmetic mean of surgically induced astigmatism (M-SIA) and the centroid of surgically induced astigmatism (C-SIA) after standard trabeculectomy. We comprised 185 eyes of 143 consecutive patients (mean age ± standard deviation, 67.7 ± 11.6 years) who underwent trabeculectomy and completed at least a 3-month routine follow-up. In all cases, the scleral flap was made at the nasal-superior location. Corneal astigmatism was measured with an automated keratometer. We calculated the M-SIA and the C-SIA using vector analysis and applied the astigmatism double angle plot. The magnitude of corneal astigmatism increased significantly, from 1.17 ± 0.92 D preoperatively to 1.77 ± 1.05 D postoperatively (paired t-test, p < 0.001). The M-SIA was 1.12 ± 0.55 D, and the C-SIA was 0.73 D @64° ± 1.02 D in the right eye group, and the M-SIA was 1.08 ± 0.48 D and the C-SIA was 0.60 D @117° ± 1.03 D in the left eye group. The C-SIA showed an astigmatic shift toward the nasal-superior location of the scleral flap creation. Our results revealed that trabeculectomy induced the SIA in the direction of the scleral flap location and that the C-SIA was much lower than the M-SIA in eyes undergoing trabeculectomy.