Predicted Refraction Versus Refraction Outcome in Cataract Surgery After Trabeculectomy

PURPOSE: To determine whether the manifest refraction after cataract surgery in eyes that had undergone previous trabeculectomy was different from the predicted refraction. SETTING: University-based tertiary glaucoma service and 3 glaucoma private practices. METHODS: Retrospective, interventional, case-control study. The medical records of patients with glaucoma and medically treated glaucoma suspects who underwent cataract extraction between January 1, 2004 and February 11, 2006 were reviewed. The axial length was measured by contact A-scan ultrasonography. The study group included 27 eyes of 25 patients who underwent phacoemulsification with intraocular lens implantation after trabeculectomy, whereas the control group included 52 eyes of 49 glaucoma patients or medically treated glaucoma suspects who underwent phacoemulsification with intraocular lens implantation only. The main outcome measure was the difference between the postphacoemulsification manifest refraction and predicted refraction between the 2 groups. RESULTS: The difference between the mean final refraction and mean predicted refraction in the study group (-0.852+/-1.056 D) and the control group (-0.501+/-0.542 D) was not statistically significant (P=0.115). The mean intraocular pressure in the study group decreased significantly after trabeculectomy (25.9+/-8.9 to 9.6+/-4.3 mm Hg, P<0.001), and increased significantly after phacoemulsification (9.6+/-4.3 to 12.5+/-5.3, P=0.001). Lower prephacoemulsification intraocular pressure was weakly correlated with a myopic shift in final refraction (r=0.269, P=0.017). CONCLUSIONS: Though numerous variables can potentially influence the refractive outcome in cataract extraction after trabeculectomy, our study shows that the refractive outcome in these cases remained reasonably predictable. However, lower prephacoemulsification intraocular pressure was weakly correlated with a myopic shift in final refraction.