The effect of prior trabeculectomy on refractive outcomes of cataract surgery.

Purpose: To examine surgical and refractive outcomes of phacoemulsification with intraocular lens (IOL) implant in eyes with prior trabeculectomy.

Design: Retrospective observational case-control study.

Methods: The study compared eyes that underwent phacoemulsification with IOL implant at least 3 months post-trabeculectomy (n = 77) with eyes with either medically controlled glaucoma (n = 43) or no glaucoma (n = 50) at an academic institution. The main outcome measure was the difference between the expected and the actual postoperative refraction.

Results: Mean intraocular pressure (IOP) increased in trabeculectomy eyes from 8.7 ± 4.2 mm Hg to 10.7 ± 4.0 mm Hg (P < .0001), whereas it decreased in glaucoma control and normal control groups by 2.0 mm Hg (P = .003) and 2.1 mm Hg (P < .00001), respectively, with concurrent decrease in drops in the glaucoma control group (0.76 to 0.23, P < .0001). The difference from expected refractive outcome was -0.36 (more myopic) in trabeculectomy eyes compared with +0.23 (more hyperopic) in nonglaucoma controls and +0.40 in glaucoma controls (P < .0001). The correlation between change in IOP vs extent of refractive surprise was statistically significant (P = .01, r = -0.20). Final visual acuity was not affected by the difference in refractive error.

Conclusions: The refractive surprise correlated to IOP change, with 2 mm Hg rise resulting in a -0.36 diopter shift between predicted and actual refraction. After cataract extraction, IOP decreased in controls and fewer drops were required, but IOP increased in the study group. Factors affecting refractive surprise in cataract surgery after trabeculectomy, especially IOP change and axial length, require further investigation.