Why Does Cataract Surgery Lower IOP in Some Patients?

Although there have been numerous reports documenting the reduction of IOP following phacoemulsification cataract extraction in both glaucomatous and nonglaucomatous eyes, the exact mechanism by which this occurs is largely unknown.

The decrease in IOP is the result of improved aqueous humor outflow through the trabecular meshwork, i.e., increased aqueous outflow facility. There does not appear to be an alteration of circadian fluctuation of IOP, except perhaps in eyes with pseudoexfoliation. Clinical observations strongly implicate a biomechanical effect. There are mounting data that the degree to which cataract extraction increases the anterior chamber angle depth correlates to the degree of IOP lowering.

There has been one investigation into a possible molecular mechanism. Joel Schuman's laboratory found that trabecular meshwork endothelial cells from glaucomatous eyes that were exposed to ultrasound had increased interleukin-1α (IL-1 α), a stress hormone and pathologic marker for primary open-angle glaucoma, through NFκB translocation from the cytoplasm into the nucleus. Further investigation is needed to fully elucidate the cellular and molecular events.