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Less is more with glaucoma surgery
Targeting the placement of the iStent can help surgeons achieve greater success.
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The glaucoma surgery procedure profile has expanded, with many choices for the surgeon to utilize to assist in the management of sight-threatening glaucoma, while decreasing the potential iatrogenic and procedure-specific complications that can be associated with some of these procedures, depending on their degree of invasiveness. Microinvasive glaucoma surgery, as the name implies, is relatively less invasive compared with filtration procedures, and hence the subset of patients who have both glaucoma and cataract can greatly benefit from a single combined surgical procedure that addresses both the cataract and open-angle glaucoma. According to the World Health Organization’s 2002 report, the two significant sources of global visual impairment are cataract, accounting for 17 million people, and glaucoma, representing 4.4 million individuals.
The avenues of MIGS include increasing aqueous outflow through the trabecular outflow system, suprachoroidal space and subconjunctival space, in addition to decreasing aqueous production via cycloablative procedures. These tools provide a relative decrease in potential surgical complications while decreasing the overall effectiveness of lowering IOP as compared with more invasive procedures such as trabeculectomy and Ex-Press shunt implantation (Alcon). All of these procedures have a relative place in the overall surgical management of open-angle glaucoma, and it is important to choose the best glaucoma procedure for the individual patient. A patient who undergoes cataract surgery for visual rehabilitation can clearly benefit from the addition of a relatively lower-risk glaucoma MIGS procedure to help lower IOP and potentially decrease the number of topical glaucoma medications.
In this column, Dr. Gallardo describes the combined use of an iStent (Glaukos) with phacoemulsification and provides additional surgical pearls.
Thomas “TJ” John, MDOSN Surgical Maneuvers Editor
In my practice, I perform MIGS on virtually every patient on topical hypotensive medications undergoing cataract surgery to either reduce IOP and/or the medication burden. For patients with open-angle glaucoma who are controlled on medications and are undergoing cataract extraction, I automatically couple the surgery with a MIGS procedure to reduce or eliminate the need for topical medications. I do so because topical medications can cause significant pathologic changes to the eye and ocular adnexa. More importantly, benzalkonium chloride is known to be pro-apoptotic and leads to a loss of the endothelial cells lining columns of the trabecular meshwork.
Before the advent of MIGS, I would often couple a cataract surgery with a filter if a patient had uncontrolled glaucoma on maximum tolerated medical therapy. Now, because of the efficacy and safety profile, I almost always use a MIGS procedure, specifically iStent implantation, before discussing a filter. In my experience with the iStent over the past 4 years, I have been able to control the uncontrolled, while even dropping medication burden. But more impressive, the iStent has been able to drastically reduce my need for filtering procedures.
Pearls for placement and targeting
When the eye is depressurized, blood regurgitates into the canal and can be seen through the transparent trabecular meshwork. Blood in the canal confirms that area of the canal is patent and connected to a functioning distal system. Blotches of heme within areas of regurgitation signify locations of collector channels (Figure 1), which is the ideal site for iStent implantation. Once the iStent is implanted, visualization of blood regurgitation through or around the iStent’s nozzle confirms the iStent is seated correctly within the canal and in an appropriate location. We can also use the pattern of pigmentation in the trabecular meshwork overlying Schlemm’s canal. Because the endothelial cells lining the trabecular columns are phagocytic, areas of higher aqueous outflow tend to have a higher degree of pigmentation. Targeting these areas also helps to maximize efficacy, as outflow is augmented and allows for aqueous to reach the distal system with less resistance.
After evaluation of the visual cues during intraoperative gonioscopy and intelligent iStent implantation, we can also evaluate the patency of the distal outflow system by evaluating the degree of blanching of the episcleral venous system during anterior chamber evacuation of viscoelastic with the irrigation and aspiration handpiece and/or pressurization of the anterior chamber (Figure 2). When the viscoelastic is evacuated and the anterior chamber is pressurized with balanced salt solution, fluid is forced through the iStent and the outflow system, causing the episcleral vessels to blanch. This confirms communication between the anterior chamber and a patent episcleral system via the iStent. As confirmation of ideal iStent placement, I like to see both blood regurgitation through the iStent and blanching of the episcleral system.
Source: Mark J. Gallardo, MD
The thought of iStent targeting, or “intelligent placement,” can be daunting when first adopting the technology. A simple understanding of the anatomy, pathologic changes and visual cues that help highlight areas for implantation can easily help new surgeons achieve great success very rapidly. It is worth the effort to invest the time to learn how and where to implant the iStent because of the safety profile affiliated with the device. As large areas of the blood-aqueous barrier are not ablated, as with other MIGS devices on the market, there is no fear of placing a patient at risk for developing recurrent hyphemas. Also of great importance, iStent placement does not preclude us from performing any other angle-based surgery, if needed, in the future.
I believe that utilizing the conventional outflow system is the safest course of action for the treatment of glaucoma. It can achieve needed pressure and medication reduction while eliminating the risk of sight-threatening complications affiliated with more aggressive procedures that can lead to hypotony and all that hypotony implies. Surgeons, once committed to understanding iStent technology, the basis for its safety profile compared with other procedures, and the mechanics of implantation, seem to successfully incorporate the procedure long term into their clinical practice.
- References:
- Ammar DA, et al. Mol Vis. 2011;17:1806-1813.
- Chang C, et al. Clin Exp Ophthalmol. 2015;doi:10.1111/ceo.12390.
- Gallardo M. Intraocular pressure control with reduced medication burden after cataract surgery and ab interno trabecular stent implantation for OAG and cataract. Presented at: American Society of Cataract and Refractive Surgery annual meeting; May 7, 2016; New Orleans.
- Neuhann TH. J Cataract Refract Surg. 2015;doi:10.1016/j.jcrs.2015.06.032.
- Resnikoff S, et al. Bull World Health Organ. 2004;82(11):844-851.
- For more information:
- Mark J. Gallardo, MD, is an ophthalmologist and glaucoma specialist with El Paso Eye Surgeons in El Paso, Texas. He can be reached at email: gallardomark@hotmail.com.
- Thomas “TJ” John, MD, is a clinical associate professor at Loyola University at Chicago and is in private practice in Oak Brook, Tinley Park and Oak Lawn, Illinois. He can be reached at email: tjcornea@gmail.com.
Disclosures: Gallardo reports he is a speaker, consultant and clinical investigator for Glaukos, Alcon and Ellex; clinical investigator for Sight Sciences and Ivantis; clinical investigator for New World Medical; and speaker for Aerie and Bausch + Lomb. John reports no relevant financial disclosures.