Surgically induced astigmatism after phacotrabeculectomy: a prospective observational study at ECWA Eye Hospital, Kano

Combined phacotrabeculectomy is commonly performed in patients with coexisting cataract and primary open angle glaucoma to achieve simultaneous visual rehabilitation and intraocular pressure control. However, the procedure may induce corneal astigmatic changes that influence postoperative visual outcomes. This study prospectively evaluated the magnitude and temporal changes of surgically induced astigmatism following phacotrabeculectomy using both arithmetic and vector analytic methods. This hospital based prospective observational study was conducted at ECWA Eye Hospital, Kano, Nigeria, between July 2024 and June 2025. Adults aged 40 years or older with visually significant age-related cataract and primary open angle glaucoma who underwent single site superior phacotrabeculectomy were enrolled and followed for 12 weeks. Corneal astigmatism was measured preoperatively and at postoperative weeks 1, 6, and 12. Surgically induced astigmatism was calculated using arithmetic subtraction and vector analysis based on the Alpins method. Temporal changes in surgically induced astigmatism and intraocular pressure were evaluated using linear mixed effects modeling. Sixty-three participants completed follow up. Mean arithmetic surgically induced astigmatism decreased from 1.46 ± 0.90 D at week 1 to 0.03 ± 0.81 D at week 12. Mean vector surgically induced astigmatism decreased from 2.41 ± 1.54 D to 1.52 ± 0.96 D over the same period. Centroid astigmatism reduced progressively over time. Linear mixed model analysis demonstrated a significant effect of time on surgically induced astigmatism (F (2,124) = 16.89, p < 0.001). Vector analysis yielded greater magnitudes than the arithmetic method ( p = 0.001). Intraocular pressure decreased from 18.89 ± 4.81 mmHg preoperatively to 14.63 ± 3.46 mmHg at week 12 ( p < 0.001). Phacotrabeculectomy is associated with an early increase in corneal astigmatism followed by gradual reduction over time, with a trend toward relative stabilization by 12 weeks. Vector analysis provides a more comprehensive assessment of surgically induced astigmatism than arithmetic subtraction by accounting for changes in both magnitude and axis. These findings support appropriate timing of postoperative refractive assessment and highlight the relevance of preoperative astigmatism when considering refractive planning in combined cataract and glaucoma surgery.