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M. S. Muallem, G. A. Nelson, S. Osmanovic, R. Quinones, M. Viana, D. P. Edward; Predicted Refraction versus Refraction Outcome in Cataract Surgery Following Trabeculectomy. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1090.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether the manifest refraction following cataract extraction by phacoemulsification with intraocular lens implantation in eyes that had undergone previous trabeculectomy was different from the predicted refraction.
Retrospective, interventional, case-control study. The medical records of patients with glaucoma and medically treated glaucoma suspects who underwent cataract extraction 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, while 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 post-phacoemulsification manifest refraction and predicted refraction between the two groups.
The difference between the final refraction and 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 intraocular pressure (IOP) 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), while in the control group there was no significant difference (p=0.758) between the pre-phacoemulsification (15.5±3.9 mm Hg) and post-phacoemulsification (15.3±3.6 mm Hg) IOP. The IOP was significantly higher in the control group compared to the study group both before (15.5±3.9 vs. 9.6±4.3, p<0.00001) and after phacoemulsification (15.3±3.6 vs. 12.5±5.3, p=0.006). Lower pre-phacoemulsification IOP was weakly correlated with a myopic shift in final refraction (r=0.269, p=0.017). The time interval between phacoemulsification and postoperative best manifest refraction was not significantly different between the groups (228.6±236.1 vs. 207.1±208.3 days, p=0.68).
Though numerous variables can potentially influence the refractive outcome in cataract extraction following trabeculectomy (such as changes in corneal curvature, anterior chamber depth and intraocular pressure, and possible error in measuring the axial length with A-scan ultrasonography due to the potential deformation of the eye with the probe following trabeculectomy resulting in falsely low readings), our study shows that the refractive outcome in these cases remained reasonably predictable.
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