Minimally Invasive Glaucoma Surgery

Minimally invasive procedures are set to transform the care of glaucoma patients and have been shown to lower intraocular pressure (IOP) and/or medication usage in large clinical trials. These procedures are appealing from a patient perspective because of their improved safety profile and faster recovery, compared to more invasive procedures.

Traditionally, glaucoma has been treated with medications and/or laser; with surgery often reserved for advanced disease progressing on multiple medications where vision is threatened. This is because of the potential for sight-threatening complications from invasive procedures such as trabeculectomy with mitomycin. However with the advent of MIGS, surgery is now a viable option earlier in the disease process. These procedures can be performed alone or in combination with elective cataract surgery,¹ making them an even more attractive proposition to patients.

This article reviews the latest minimally invasive glaucoma surgical procedures to equip optometrists in appropriately managing and referring patients who require glaucoma surgery. We discuss how to identify patients who may benefit from MIGS and provide expectations of post-operative management. With advances in glaucoma surgery, optometrists will play an increasingly important role in providing pre- and post-operative support for glaucoma patients.

The Hydrus… material is well-proven and has been used in over one million medical implants

iStent

The iStent is a 1mm long heparin-coated titanium device that is inserted into Schlemm’s canal at the time of cataract surgery to lower IOP and reduce or eliminate the need for glaucoma medication. The iStent is the smallest implant approved for use in the human body and is safe in magnetic resonance imaging (MRI) scanners. The device is inserted using the same incisions as cataract surgery and the device remains permanently in Schlemm’s canal to increase aqueous outflow. Clinical trials have shown a significant decrease in IOP over periods of up to four years along with a significant decrease in medication usage following iStent insertion.² Other studies have shown that the insertion of two iStents provides an even greater reduction in IOP and medication use.³

In Australia, a second-generation iStent is available called the iStent Inject. It has a new design and comes preloaded with two stents. In clinical trials it has been shown to be at least as effective as two medications.⁴

The iStent should be considered in all patients with mild-to-moderate open angle glaucoma treated with eye drops who are undergoing cataract surgery. Potential benefits to the patient include a reduction in IOP and/or need for glaucoma medication. The latter may be particularly beneficial in patients who are experiencing side effects from their glaucoma medication or have difficulty adhering to regular medication use. Patient recovery is rapid, allowing a quick return to normal activities.

Post-operatively, patients are treated with topical chloramphenicol antibiotic drops for seven days. Topical steroids are prescribed four times a day initially and tapered over one to two months. Glaucoma medication should be continued initially and discontinued as IOP improves.

The iStent has an excellent safety profile and no major complications have been reported in the literature relating to the iStent itself. Potential complications include stent malposition or stent obstruction, however these can be resolved with YAG laser to the stent opening or secondary stent implantation if required.

Hydrus Microstent

The Hydrus is a curved flexible stent that is approximately the size of an eyelash. Once inserted, it acts like a scaffold to widen and dilate Schlemm’s canal to enhance aqueous outflow. Like the iStent, it is inserted using the same incisions as cataract surgery and remains permanently in Schlemm’s canal. It has a 1mm inlet portion that remains in the anterior chamber and this can be checked on gonioscopy. The Hydrus is made of an alloy called nitinol that is both biocompatible and MRI-safe. This material is well-proven and has been used in over one million medical implants. A large randomised clinical trial has shown that Hydrus is both safe and effective at reducing IOP.⁵

Similar to the iStent, the Hydrus should be considered in all patients with mild-to-moderate open angle glaucoma treated with eye drops who are undergoing cataract surgery. The potential advantages to the patient include a lowering of IOP, the major modifiable risk factor for the development and progression of glaucoma, and a reduction in glaucoma medication burden. We know from large surveys of glaucoma patients that over 50 per cent experience side effects including ocular discomfort, redness, and blurred vision.⁶ The use of MIGS may be a more patient-friendly way to lower IOP than glaucoma medications.

The post-operative care of Hydrus patients is similar to the iStent. Patients are prescribed topical antibiotics and steroids four times a day initially. The use of topical steroids may be supplemented with a topical non-steroidal anti-inflammatory medication routinely or in selected patients. Topical antibiotics are stopped after seven days and steroids are tapered over one to two months. As with the iStent, glaucoma medications should be continued initially and can be reduced or stopped as IOP improves.

XEN Gel Glaucoma Implant

The XEN is a revolutionary new minimally invasive procedure that drains aqueous to the subconjunctival space, the same location as gold standard trabeculectomy surgery. The XEN is a flexible collagen tube, only 6mm in length, that is inserted via a self-sealing clear corneal incision in a 15-minute operation under local anaesthetic. The length of the tube and size of the lumen have been specifically designed to regulate aqueous drainage from the eye and prevent hyotony, a serious complication that can occur following trabeculectomy. Unlike trabeculectomy there is no cutting or suturing required with the XEN, resulting in a safer operation and much faster postoperative recovery.

The XEN provides a much less invasive operation than trabeculectomy while maintaining efficacy. In a clinical study, there was an average IOP reduction of 36.4 per cent following XEN insertion and a 57 per cent reduction in glaucoma medication use.⁷ In this study nine out of 10 patients achieved an IOP of 18 mmHg or less and 40 per cent were entirely medication free.⁷

The XEN can be inserted alone or in combination with cataract surgery. Because of its superior IOP lowering, the XEN is suitable for patients with glaucoma as an alternative to trabeculectomy where IOP is not controlled with eye drops and/or laser treatment. The XEN seems most appropriate for those who do not have very advanced glaucoma.

Post-operatively patients are prescribed topical antibiotics four times a day and topical steroids between four and eight times a day to prevent excessive healing. Compared to trabeculectomy, the return of clear vision is much more rapid.

Fortunately, serious complications are rare. Apart from hyphaema, the risks in the early post-operative period are low pressure and high pressure. For this reason, patients should be reviewed closely by their surgeon to ensure optimal outcomes.

CyPass

The CyPass is a new treatment option for glaucoma that effectively lowers IOP and medication burden by allowing aqueous to drain from the anterior chamber to the suprachoroidal space. This novel device enhances the natural uveoscleral outflow of the eye; using the negative pressure gradient between the suprachoroidal space and anterior chamber. The CyPass is 6.35mm long and is inserted via a self-sealing clear corneal incision between the ciliary body and sclera. The procedure takes between 10 and 15 minutes and can be performed under local anaesthetic. The procedure can be performed alone or in combination with cataract surgery. In a large randomised clinical trial, 77 per cent of patients treated with the CyPass achieved a 20 per cent or more reduction in IOP and 85 per cent of patients were medication-free at 24 months.⁸

The CyPass represents an exciting new option for patients with mild-to-moderate open-angle glaucoma undergoing cataract surgery. The CyPass may also be a good option in patients where trabeculectomy or tube surgery has failed because it is not affected by scarring in the subconjunctival space.

The CyPass has an excellent safety profile and because it is a ‘bleb-less’ procedure it avoids the risks of bleb-related infections and other bleb-related adverse events. Fortunately, serious complications such as bleeding, infection, and hypotony are rare.

Post-operatively patients are treated with the same drops as used after cataract surgery – topical antibiotics four times a day for seven days and topical steroids four times a day for one month. Glaucoma medications are continued in the early post-operative period and reduced as IOP improves.

Conclusion

The advent of MIGS is set to transform the care of patients with glaucoma. These devices have been proven to decrease IOP and reduce reliance on glaucoma medications. By reducing medication burden, MIGS represents a more patient-friendly approach, especially for patients struggling with the side effects, cost, inconvenience, and adherence with regular eye drop use.

Australian patients with glaucoma are now fortunate to have access to a number of MIGS procedures. The iStent Inject is approved by the Therapeutic Goods Administration (TGA) for use in Australia and the Hydrus, XEN, and CyPass are available to select glaucoma specialists as part of a careful rollout of these devices.

Knowledge of the latest surgical options in glaucoma will help optometrists best care for their patients by identifying those who may benefit from MIGS and co-managing patients who have undergone these procedures.

Dr. Nathan Kerr is a fellowship-trained glaucoma subspecialist in Melbourne. Dr. Kerr specialises in minimally invasive glaucoma surgery (MIGS) and completed a Glaucoma Fellowship at Moorfields Eye Hospital in London where he trained in MIGS under the world-renowned surgeon Keith Barton. Dr. Kerr was the first Australian surgeon to be accredited in the use of the XEN Gel Implant and is co-editor of MIGS.org, a leading source of patient information on glaucoma surgery created in collaboration with the International Glaucoma Association. He has been invited to teach MIGS surgery in the United Kingdom, Switzerland, France, and Australia. He is a consultant ophthalmologist at the Royal Victorian Eye and Ear Hospital and consults privately at Eye Surgery Associates in East Melbourne and Vermont. doctorkerr.com.au

Keith Barton is a glaucoma specialist at Moorfields Eye Hospital and Editor-in-Chief of the British Journal of Ophthalmology. His research interests include the surgical management of glaucoma, specifically minimally invasive glaucoma surgery and the use of aqueous shunt devices. He is chairman of the International Glaucoma Association and co-editor of MIGS.org.

References
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2. Fea AM, Consolandi G, Zola M, et al. Micro-Bypass Implantation for Primary Open-Angle Glaucoma Combined with Phacoemulsification: 4-Year Follow-Up. J Ophthalmol 2015;2015:795357. doi:10.1155/2015/795357.
3. Katz LJ, Erb C, Carceller GA, et al. Prospective, randomized study of one, two, or three trabecular bypass stents in open-angle glaucoma subjects on topical hypotensive medication. Clin Ophthalmol 2015;9:2313-2320. doi:10.2147/OPTH.S96695.
4. Fea AM, Belda JI, R?kas M, et al. Prospective unmasked randomized evaluation of the iStent inject (®) versus two ocular hypotensive agents in patients with primary open-angle glaucoma. Clin Ophthalmol 2014;8:875-882. doi:10.2147/OPTH.S59932.
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6. Kerr NM, Patel HY, Chew SS, Ali NQ, Eady EK, Danesh-Meyer HV. Patient satisfaction with topical ocular hypotensives. Clin Experiment Ophthalmol 2013;41(1):27-35. doi:10.1111/j.1442-9071.2012.02823.x.
7. Sheybani A, Dick HB, Ahmed IIK. Early Clinical Results of a Novel Ab Interno Gel Stent for the Surgical Treatment of Open-angle Glaucoma. J Glaucoma 2016;25(7):e691-6. doi:10.1097/IJG.0000000000000352.
8. Vold S, Ahmed IIK, Craven ER, et al. Two-Year COMPASS Trial Results: Supraciliary Microstenting with Phacoemulsification in Patients with Open-Angle Glaucoma and Cataracts. Ophthalmology 2016;123(10):2103-2112. doi:10.1016/j.ophtha.2016.06.032.