Glaucoma is often caused by a buildup of pressure inside the eye, or intraocular pressure (IOP), which causes damage to the optic nerve. Most patients have no early symptoms or pain – but if left untreated, it can cause total permanent blindness within a few years.
Sometimes, glaucoma can also be caused by a blunt or chemical injury to the eye, severe eye infection, blocked blood vessels inside the eye or other inflammatory conditions. On rare occasions, an unrelated eye surgery can also cause glaucoma.
A Revolution in Glaucoma Surgery
Some of the treatments for glaucoma include prescription eye drops and laser surgery to reduce eye pressure and halt any damage to the optic nerve. Previously, there were limited surgical options for patients with mild to moderate glaucoma, but with the latest minimally invasive glaucoma surgery
(MIGS) procedures available today, there are a wider range of treatment alternatives for patients. MIGS involves creating a tiny incision to implant a microscopic-sized device, which reduces IOP and slows the progression of glaucoma. The procedure is often touted as much safer, as it causes fewer complications compared to conventional surgeries, and involves a shorter recovery time than more invasive techniques.
Some doctors like to start with medications, but early laser surgery or microsurgery may actually work better for some patients, like in babies, for instance, where the cause of congenital glaucoma is a very distorted drainage system.
Dr. Chelvin Sng, a consultant at the National University Hospital in Singapore, said she uses a variety of MIGS devices in her practice. These include both iStent trabecular micro-bypass stent and the iStent Inject from Glaukos (San Clemente, California, U.S.A.), the XEN Gel Implant from Allergan (Dublin, Ireland), and the InnFocus Microshunt from Santen (Osaka, Japan).
All About iStent
The iStent is a tiny snorkel-like device that bypasses the blockage in the trabecular meshwork to lower and control pressure within the eye.
“The iStent has a very high safety profile but is more modest in terms of efficacy, with the IOP-lowering effect limited by the episcleral venous pressure,” explained Dr. Sng.
“Hence, it is more appropriate as a phaco-plus procedure in patients with mild-to-moderate glaucoma controlled on medications, who would like to decrease their medication burden after the surgery. The target IOP of these patients should be in the mid-to-high teens. In general, trabecular bypass procedures are not suitable for patients with very advanced glaucoma who are on multiple medications,” she said.
Elaborating further on the various options she uses, Dr. Sng said: “These MIGS devices differ in terms of efficacy, anatomical location and safety profiles making them appropriate for different types of patients.”
XEN Implant vs. InnFocus Microshunt
The XEN Gel Implant and InnFocus Microshunt both use tiny, microscopic-sized tubes that can be inserted into the eye and drain fluid from inside the eye to underneath the outer membrane of the eye (conjunctiva).
According to Dr. Sng, the most distinctive feature of the XEN implant is that it is implanted ab-interno (from the inside of the eye) through a clear corneal incision, without requiring conjunctival peritomy.
“This results in a shorter surgical duration, faster recovery and less complications… for example, bleb leak,” she noted. On the other hand, without conjunctival peritomy, the implant may be frequently occluded by Tenon’s capsule, hence the postoperative needling rate is high, at approximately 30 percent in her practice.
In contrast, the InnFocus Microshunt is an ab-externo (from outside the eye) subconjunctival MIGS device, which requires conjunctival peritomy and sub-Tenon’s dissection.
Early results have suggested that it can potentially be used for advanced glaucoma, and a randomized controlled study comparing the InnFocus Microshunt with trabeculectomy is currently underway.
“In general, subconjunctival MIGS devices are more effective in lowering the IOP compared with trabecular bypass procedures and are able to achieve lower postoperative IOP. However, they are associated with a higher risk profile with potential bleb-related complications, and the surgeon would need to be skilled in post-operative bleb management.”
“Appropriate patient selection is key to the success of any glaucoma surgery, and the surgeon must weigh the importance of safety versus efficacy in each patient and select the most appropriate MIGS device,” advised Dr. Sng.
Breakthroughs and Innovation
The future looks bright with more breakthroughs to be expected for MIGS. According to Dr. Sng: “There is currently a renaissance in glaucoma surgery, with many novel and innovative devices introduced in recent years.
I anticipate that this momentum in innovation will persist, and we will have access to even more devices with better predictability, efficacy and safety profiles in the future.”
“Besides new surgical devices, I anticipate that there will also significant progress made in the area of drug delivery, with sustained-release glaucoma medications available which can be administered in the clinic. Such developments will greatly improve patient compliance and quality of life,” she concluded.
Could the Future be XEN?
Dr. Cameron Hudson, international director for XEN at Allergan, said that XEN has a number of differentiating properties compared to other glaucoma procedures and devices, and remains the only ab-interno procedure capable of providing subconjunctival outflow.
XEN is recommended for the management of refractory glaucomas, including cases where previous surgical treatment has failed or in pigmentary glaucoma with open angles that proved unresponsive to maximum tolerated medical treatment.
“For patients failing on existing therapy, XEN offers powerful and sustained IOP reduction without the need for significant dissection of the conjunctival and other ocular tissues,” explained Dr. Hudson.
“Evidence shows favorable visual rehabilitation in patients who have received the XEN device, and compatibility with future treatment options is an area of current investigation where we expect to see further merit of the procedure,” he added. “With the advent of recent devices, XEN included, it’s clear that industry and professional partners share a common goal to make glaucoma surgery safer.”
He said that safety is an important goal because around one in five glaucoma patients is poorly served by medical therapies and is progressing due to inadequate IOP control, or is burdened by adverse side effects of drops.
What’s clear is that for patients with glaucoma, lost vision can’t be restored. However, lowering eye pressure can help preserve the remaining vision. With the latest in cutting-edge technology in MIGS, patients can look forward to easier, better and safer treatments than ever before.