Prior trabeculectomy may contribute to refractive surprise after cataract surgery

This retrospective study found that postoperative refractive shift correlated to IOP change in cataract patients with prior trabeculectomy. This could have widespread implications for how we choose the correct IOL for various subsets of patients.

The authors retrospectively evaluated refractive outcomes in 65 cataract patients (77 eyes) with prior trabeculectomy and in controls with or without glaucoma and no prior trabeculectomy.

Patients with prior trabeculectomy had significantly greater refractive error than expected. The refractive difference correlated to IOP change, with a 2 mmHg rise resulting in a -0.36 D shift. Control eyes, on the other hand, showed a 2.0 mmHg decrease in IOP and a corresponding +0.23 refractive change in nonglaucomatous eyes and +0.40 change in glaucomatous eyes.

The correlation between change in IOP and extent of refractive change was statistically significant. Final visual acuity was not affected by the difference in refractive error.

The authors propose that phacoemulsification after trabeculectomy increases IOP, perhaps through postoperative intraocular inflammation causing increased fibrosis of the trabeculectomy bleb, which causes an increase in axial length and a resulting myopic shift.

They write that cataract surgeons should be aware of the potential for increase in IOP and resultant increase in axial length postoperatively, with low pressures attributable to functioning filtering blebs. The axial length of the fellow eye, if no trabeculectomy has been performed, may be useful in selecting the power of the lens implant.