January 2014

 

GLAUCOMA

 

The role of cataract surgery in glaucoma management


by Tony Realini, MD

   
cataract surgery

iStent next to the I/A tip following placement. In clinical trials, IOP <21 mm Hg on no medications 12 months postoperatively was achieved by 72% of iStent eyes and 50% of cataract alone eyes.

Source: Jonathan D. Solomon, MD

Emerging data suggest cataract surgery may provide a significant reduction in intraocular pressure

Both cataract and glaucoma are diseases related to aging. Both become more common as we get older. As Americans live longer and the population ages, the number of our patients with both cataract and glaucoma is going to increase.

The two conditions can be managed completely separately from one another, and often are. However, emerging data suggest that cataract surgery alone can provide significant IOP reduction. Is there a role for cataract extraction in the management of glaucoma, and does the diagnosis of glaucoma alter the indication for cataract surgery?

Cataract surgery lowers IOP

Numerous studies have demonstrated that IOP goes down after cataract surgery. Most of these studies have important limitations and caveats. One of the most compelling studies demonstrating the effect of cataract surgery on IOP is a recent post hoc analysis from the Ocular Hypertension Treatment Study (OHTS).

"Among this well-characterized ocular hypertensive cohort, phacoemulsification decreased IOP by 4.0 mm Hg, a 16.5% drop from preoperative IOP," in 63 untreated subjects in the observation arm, according to James Brandt, MD, University of California, Davis. "This effect was sustained for at least one year without medication."

This is a substantial effect. As a benchmark, 4 mm Hg is as much or more than would be expected when adding any adjunctive therapy to a prostaglandin.

"But can we assume that phaco alone generally result in an IOP drop of about 4 mm Hg in our glaucoma patients? Probably not," he said.

He pointed out that patients in OHTS did not have glaucoma, and those in the observation arm were on no medications. This is very different from our glaucoma patients on medical therapy who undergo cataract surgery, he said, and the OHTS findings may not apply to them. Even more recently, we have learned the power of cataract surgery in lowering IOP from the several so-called microinvasive glaucoma surgery (MIGS) procedures that have been developed and evaluated as add-on therapies at the time of cataract surgery. The iStent trabecular micro-bypass shunt (Glaukos, Laguna Hills, Calif.) has been approved for this indication. In clinical trials, IOP reduction was compared in eyes undergoing cataract surgery and iStent implantation versus cataract surgery alone. In the key registry trial, glaucoma patients with IOP <24 mm Hg on one to three medications randomly underwent cataract surgery with or without iStent placement. The primary outcome—IOP <21 mm Hg on no medications 12 months postoperatively —was achieved by 72% of iStent eyes and 50% of cataract alone eyes (p<0.001). This result was adequate to garner FDA approval. It is worth noting that 50% of patients undergoing cataract surgery alone enjoyed significant IOP reduction accompanied by elimination of the need for medications. In fact, the average IOP reduction after cataract surgery alone was 8.5 mm Hg. However, many of these patients were back on medications a year after surgery, so this result is not directly comparable to the OHTS result.

How does cataract surgery lower IOP?

The mechanism by which cataract surgery lowers IOP involves enhanced trabecular outflow, said Douglas Rhee, MD, Case Western Reserve University, Cleveland.

"The extent to which phacoemulsification lowers IOP is correlated to the degree of anterior chamber deepening postoperatively," he said. "In fact, eyes with narrow angles preoperatively enjoy greater IOP reductions than eyes that are relatively deep preoperatively."

In addition to this mechanical mechanism, there may be molecular mechanisms in play.

"In an in vitro study of cultured human trabecular meshwork cells, the stress hormone interleukin-1 alpha is released from the trabecular meshwork of glaucomatous but not healthy eyes when exposed to ultrasound," Dr. Rhee explained.

This mechanism may play a role in mediating IOP reduction after cataract surgery in glaucomatous eyes, he said, "but molecular mechanisms that might be at play in non-glaucomatous eyes remain elusive."

Clinical impact

Dr. Brandt has developed a checklist for decision-making in glaucoma patients with cataract.

It begins with staging the glaucoma. "Determine a target IOP. Is cataract surgery with or without MIGS going to get you there?"

Then, perform gonioscopy. "We perform this at diagnosis, but we don't always repeat it over time, so we may miss progressive angle narrowing, which can help identify patients most likely to enjoy an IOP reduction after cataract surgery."

He also recommends thinking ahead of time about what your options may be for managing potential IOP spikes postoperatively, considering patient life expectancy when setting targets and planning interventions, and managing expectations for surgical outcomes proactively.

Dr. Brandt feels that in patients with mild glaucoma, cataract surgery alone may be an appropriate first surgical intervention, although there may be a role for ab interno procedures such as the iStent because they do not involve the conjunctiva, which may be needed for conventional filtering surgery later in the disease process.

"Glaucoma specialists are a conservative lot—we take the long view in managing a slowly progressive disease and are painfully aware that our surgical procedures last only 5–10 years in most patients," he said. "Keeping options open for patients who are living longer and longer is an important part of the equation."

Editors' note: Dr. Rhee has financial interests with Alcon (Fort Worth, Texas), Allergan (Irvine, Calif.), AqueSys (Aliso Viejo, Calif.), Merck (Whitehouse Station, N.J.), and Santen (Osaka, Japan). Dr. Brandt has financial interests with Alcon, Allergan, Carl Zeiss Meditec (Jena, Germany), and Glaukos.

Contact information

Brandt
: jdbrandt@ucdavis.edu
Rhee: dougrhee@aol.com

Related articles:

Retinal evaluation before cataract surgery by Steve Charles, MD

Immediately sequential bilateral cataract surgery: Should it be done? by Liz Hillman EyeWorld Staff Writer

Hooks and expanders ease difficult cataract surgery by Michelle Dalton EyeWorld Contributing Writer

Ethical dilemmas with femtosecond cataract surgery by Ellen Stodola EyeWorld Staff Writer

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