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Disruptive changes ahead in glaucoma space
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All of us who do cataract surgery see a significant number of patients who have glaucoma as a comorbidity. At least 10% of patients who come to have cataract surgery also have a diagnosis of glaucoma or ocular hypertension, and a review of Medicare statistics suggests the number may approach 20% in the over-65-year-old population.
During the first two decades of my practice, if a patient presented with combined cataract and glaucoma, I always recommended a combined phacoemulsification and trabeculectomy, because in those days I was invading prime conjunctiva by doing a conjunctival peritomy for my cataract surgery and operating superior. After switching to temporal clear corneal cataract surgery, I began to treat more of my patients presenting with combined cataract and glaucoma with phacoemulsification alone, reserving trabeculectomy for those who did not achieve good IOP control with phacoemulsification combined with argon or selective laser trabeculoplasty and/or topical drops.
My associates Tom Samuelson, MD, Brooks Poley, MD, and I became impressed that phacoemulsification alone was a powerful tool in the treatment of glaucoma and that those most in need presenting with higher preoperative IOP were achieving greater pressure reduction than those with lower pressure. I therefore stopped doing combined procedures altogether.
In one outstate Minnesota satellite clinical setting where I performed only phacoemulsification on 180 patients a year for a decade, with approximately a 15% incidence of glaucoma, I did not have a single patient who went on to trabeculectomy or tube shunt. We performed a retrospective review and published our findings, concluding that phacoemulsification alone can significantly reduce IOP and medication burden in the glaucoma and ocular hypertensive patient.
Perhaps the best confirmative study is the control group in the Glaukos iStent prospective FDA clinical trial, in which a mean IOP drop of 8.4 mm Hg was achieved with phacoemulsification alone in a large group of patients with mild to moderate glaucoma and a preoperative washout IOP near 26 mm Hg. Phacoemulsification alone generated an average IOP near 18 mm Hg in combination with one topical medication. Most of the patients with phacoemulsification alone will still require one or more topical drops for good pressure control, but most patients avoid the risks of a trabeculectomy or tube shunt.
The Tube Versus Trabeculectomy Study confirmed the great efficacy of these procedures, with both generating an IOP near 13 mm Hg, again typically on one topical medication. This is a lower pressure than we can achieve with phacoemulsification alone, and in patients with significant glaucoma damage in which a very low pressure is indicated, these operations remain an important tool. However, the efficacy of cataract surgery alone in reducing IOP and now the availability of an FDA-approved microinvasive glaucoma surgery (MIGS) device, the iStent, have significantly reduced the number of patients who require the much more invasive tube shunt or trabeculectomy.
As I have mentioned in previous commentaries, I consult widely in the glaucoma field, including with companies pioneering MIGS. There are many different MIGS procedures, including some that transport fluid from the anterior chamber into Schlemm’s canal, others into the suprachoroidal space, still others into the subconjunctival intra-Tenon’s space and even one that transports aqueous fluid to the ocular surface. It is too early to know which of these will be best. I suspect we will learn that each will work better for certain categories of patients, and early evidence supports the fact that they can likely also be combined to achieve lower IOP targets. My patients would like to be off all medications, so for me the ideal procedure would generate an IOP below 15 mm Hg 24 hours a day, 365 days a year with no medications.
It is clear that we have much to learn, but my patients and I are excited about the ability of the iStent when combined with phacoemulsification to reduce IOP and medication burden. I have enjoyed the privilege of traveling to Armenia to participate in a clinical trial of the iStent inject in phakic and pseudophakic eyes, in which two iStents were placed using a simpler implantation technique. Evidence is accumulating that two, and perhaps as many as three, iStents are more effective at lowering IOP and medication burden than one, and our results also showed the iStent procedure will have broad indications, adding the phakic and pseudophakic eye to the current U.S. indication for use only in combination with cataract surgery.
On this trip, I also participated in a clinical trial evaluating the safety and efficacy of the iStent Supra, which connects the anterior chamber to the suprachoroidal space. This device is similar to the Transcend CyPass device, which has completed FDA clinical trials. I was impressed with the ease of this surgical procedure, and the IOP reduction achieved in combination with cataract surgery as well as in phakic and pseudophakic eyes was quite impressive, with a low complication rate. I have also implanted the AqueSys Xen device (Allergan) in the laboratory, and this device is generating very good outcomes in Europe, where it is now commercially available. A fascinating approach developed by my Minnesota friend and colleague David Brown, MD, actually connects the anterior chamber with the ocular surface in a fashion that appears to eliminate the risk for infection. Other procedures, including endocyclophotocoagulation and the Trabectome (NeoMedix), also are increasing in popularity.
Significant intellectual and financial capital continues to be invested to advance the surgical treatment of glaucoma. I expect to see the number of trabeculectomy procedures continue to decline. Since the Tube Versus Trabeculectomy Study outcomes arguably favor tube shunts over trabeculectomy in regard to complication rate with similar efficacy, I can imagine trabeculectomy, the mainstay of glaucoma surgery during my career, disappearing completely in a decade.
With advances in MIGS and many extended-release drug-eluting devices being developed as well, I also see the use of drops to treat glaucoma progressively declining. We are in the early stages of so-called “dropless,” or at least “less drops,” approaches for infection prophylaxis and inflammation management in our cataract surgery. It appears the same trend may soon follow in glaucoma. In retina, injections of medication already dominate over treatment with drops for many indications. We seem to be traveling toward a future in which treatment of eye disease with drops will be a much less significant part of our therapy, which would be a major shift in treatment plans that have been in place not just for decades, but for centuries. The impact of these trends will be significant for patients, ophthalmologists, industry and third-party payers. Change is inevitable, and the accelerating shift away from drops in ophthalmology to surgery and extended-release drug-eluting devices for many indications is a dramatic and disruptive one indeed.
Disclosure: Lindstrom reports he is a consultant to and investor in Glaukos, Transcend Medical and AqueSys.