PHACO AND IOP

Phacoemulsification has a long-term intraocular pressure-lowering effect in both primary open-angle and angle closure glaucoma and can actually make subsequent glaucoma surgery safer. However, in eyes that have already undergone trabeculectomy, cataract surgery can imperil the functionality of the bleb, said Ingeborg Stalmans MD, PhD, UZ Leuven, Belgium.

“I think that we can say the cataract surgery does indeed play a significant role in glaucoma management,” she told attendees at a Glaucoma Day session at the XXXII Congress of the ESCRS in London.

She noted that review of literature shows that over the long term phacoemulsification reduces IOP by 1.0mmHg to 5.0mmHg in patients with primary open-angle glaucoma, and by 4.0mmHg to 13.0mmHg in patients with angle closure glaucoma.

The IOP-lowering effect is also very persistent. A chart review of patients who had undergone phacoemulsification showed that the IOP reductions measured at one year postoperatively persisted throughout six to 10 years of follow-up (Poley et al, J Cataract Refract Surg 2008 ; 34:735-742).

The proposed mechanism whereby cataract extraction produces these IOP reductions is that the removal of the lens deepens the anterior chamber and widens the iridocorneal angle. The result is an increased rearward traction from the zonule on the ciliary body, which in turn increases the outflow of aqueous through the trabecular meshwork.

IOP reduction

Research supports that theory because it shows that the narrower the iridocorneal angle is before surgery, the greater will be the reduction of IOP after phacoemulsification. Similarly, research also shows that the higher the IOP is before surgery, the greater will be the reduction in IOP afterwards. She noted that, in eyes with angle-closure glaucoma, phacoemulsification may preclude the need for further surgery. Furthermore, if surgery is necessary, the reopened angle will simplify the performance of a trabeculoplasty and also reduce the risk of malignant glaucoma after filtration procedures.

Phacoemulsification confers many of the same benefits to primary open-angle glaucoma patients. However, it does not reduce IOP to the same extent as trabeculectomy.

Phacotrabeculectomy reduces IOP more than phacoemulsification alone, but not as much as trabeculectomy alone. Therefore trabeculectomy alone may be necessary in patients who require greater reductions in IOP.

However, subsequent phacoemulsification can alter the morphology and functionality of the bleb and should therefore be delayed by at least six months after trabeculectomy to allow time for healing. A new option, minimally invasive glaucoma surgery (MIGS), which includes a range of mainly ab interno techniques, appears to have a good safety profile when combined with cataract surgery and seems to provide some additional reduction in IOP.

More trials are necessary comparing phacoemulsification with and without MIGS to assess the clinical value of the new procedures, Dr Stalmans added.

Ingeborg Stalmans: ingeborg.stalmans@uzleuven.be