Comparison of Surgically Induced Astigmatism After Glaucoma Filtering and Implant Procedures

Abstract

Purpose: To compare keratometric surgically induced astigmatism (SIA) at 3 months after trabeculectomy (LEC), EX-PRESS shunt (EXP), PRESERFLO MicroShunt (PSM), and Ahmed glaucoma valve (AGV) with ciliary-sulcus tube insertion using vector analysis, and to assess the directionality of SIA. Study Design: Single-center, nonrandomized, retrospective comparative study. Subjects and Methods: We retrospectively analyzed 100 eyes with glaucoma undergoing LEC (n = 20), EXP (n = 30), PSM (n = 30), or AGV (n = 20) at a single center. Best-corrected visual acuity (BCVA), intraocular pressure (IOP), and keratometric astigmatism were evaluated preoperatively and at 3 months postoperatively. SIA was calculated using the Jaffe vector method. Directional non-uniformity of the SIA axis was assessed using the Rayleigh test after double-angle transformation. Associations between SIA magnitude and postoperative IOP and BCVA were assessed using Spearman’s rank correlation. In the LEC group, the association between SIA magnitude and the number of residual scleral-flap sutures was also evaluated. Results: Preoperative and postoperative corneal astigmatism magnitudes did not differ significantly among the four groups. Arithmetic mean individual SIA magnitudes were 1.17 ± 0.80 D in the LEC group, 0.66 ± 0.44 D in the EXP group, 0.65 ± 0.57 D in the PSM group, and 0.58 ± 0.28 D in the AGV group (overall P = 0.035). SIA magnitude was significantly greater after LEC than after EXP, PSM, and AGV (Holm-adjusted P = 0.031, 0.031, and 0.015, respectively), whereas no significant differences were detected among EXP, PSM, and AGV. Significant directional non-uniformity of the SIA axis was detected only in the LEC group, with a circular mean axis of 19.9° (mean resultant length, 0.487; Rayleigh Z = 4.740, P = 0.007), consistent with a with-the-rule–oriented astigmatic change. No significant correlations were detected between SIA magnitude and postoperative IOP or BCVA in any surgical group. In the LEC group, SIA magnitude was not significantly correlated with the number of residual scleral-flap sutures. Conclusions: At 3 months, LEC was associated with greater keratometric SIA than EXP, PSM, and AGV. Significant with-the-rule–oriented directional non-uniformity was detected only after LEC. Plain Language Summary: Glaucoma surgery can change the curve of the cornea and cause astigmatism. This can affect how clearly a person sees after surgery. We compared corneal astigmatism 3 months after four glaucoma operations: trabeculectomy, EX-PRESS shunt, PRESERFLO MicroShunt, and Ahmed Glaucoma Valve surgery. Trabeculectomy was associated with a larger astigmatic change than the other three operations. After trabeculectomy, the astigmatic changes also tended to point in a similar direction. We did not detect this pattern after the other procedures. These findings suggest that different glaucoma procedures may affect the shape of the cornea differently after surgery. This information may help ophthalmologists anticipate early postoperative visual changes and discuss these possible changes with patients when selecting a glaucoma surgical procedure.