 | Glaucoma: What Every Patient Should Know |  |
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| Glaucoma: What Every Patient Should Know | |
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There are a variety of other surgical procedures for glaucoma to treat glaucoma, some of which have been tested for 10 years and others that are newer. These have become very frequently performed, especially in combination with cataract surgery, so a vast experience is being produced recently. They range from variations in operations that have been in use for a long time to those that use relatively new concepts and devices. Our treatment of glaucoma was greatly benefited by development of trabeculectomy and tube-shunt surgery, so further improvements or additional choices for particular situations will be valuable.
The newer operations to be considered are the FDA-approved procedures that all share the feature that they work by trying to get the aqueous humor out of the eye better to lower eye pressure. A term that has been applied to some of these is minimally invasive glaucoma surgery (MIGS). All require at least one or more incisions in the eye and some include the permanent implantation of artificial devices in the eye. As yet, the consensus of many experts is that one or more of these procedures will find a place to treat milder glaucoma with surgery when only a modest lowering of eye pressure is needed. Some have been compared to cataract surgery’s eye pressure lowering in trials where some eyes get the cataract surgery alone and some eyes get the new procedure and cataract surgery. None has been compared head to head with each other, nor to trabeculectomy, for example.
One group of procedures surgically alters the trabecular meshwork, typically by removing it along part of the whole circumference of the inner eye. The rationale is to reduce the resistance to fluid outflow. To do this, two procedures remove some of the meshwork, one with a two-bladed knife that is like beginners ice skates (Kahook Dual Blade), and the other with a cautery that removes meshwork by heating it (Trabectome). The others thread a suture or special thin device into the canal behind the meshwork, run them all around to the starting point, then pull to break through the entire meshwork (OMNI, Trab 360, GATT). These are actually similar to procedures that have been successfully used in children with glaucoma, called goniotomy and trabeculotomy (see section Children and glaucoma). These older angle procedures work well in children, but were abandoned when they failed to help adult glaucoma. The developers of the more recent operations are trying to improve on this success rate in adults through various measures.
The success in achieving eye pressure lowering for these procedures has been given in many case series, that is, groups of patients all of whom were treated by the technique, often with favorable outcome. Their potential advantage over trabeculectomy or tube-shunt surgery would be the lack of later dysfunctionally low eye pressure, and the lack of later leakage from a bleb, tube extrusion, or infection. Of course, early infection from the time of initial surgery would be possible. The time during which instruments are placed into the eye is substantially longer than with trabeculectomy or tube-shunt. Repeated later bleeding from the meshwork has occurred with this group of procedures.
Another group of procedures places a device into the meshwork to attempt to improve outflow (iStent, Hydrus). These There are stents made of metal inserted into the trabecular meshwork with the concept that the opening in the stent will provide an outflow channel to lower eye pressure better. The FDA has only approved these surgeries for patients who are also undergoing cataract surgery at the same time, and in each case the initial results suggested that the stent gave significantly lower eye pressure than cataract surgery alone. By 2 years after iStent placement, this effect was no longer present, and newer versions of the device are being developed. The Hydrus was just approved by the FDA in 2018, so longer term outcomes are not yet available.
Inserting stents adds a few minutes to cataract surgery. All materials in eye surgery devices are safe for an MRI scanner and you would not set off the TSA metal detector. There have been no reported problems with this group of devices eroding out of the eye, falling out of place, or causing damage to the eye otherwise, so their safety level is very good. Such was not the case for a device called CyPass, which was also an artificial tube-like device placed at cataract surgery, but into the space between the two layers called choroid and sclera with its open end in the front chamber of the eye. Like the other stents, it was intended to lower eye pressure, but by letting aqueous out through the uveoscleral pathway. Approved in 2016 by the FDA, it was removed from use by the company in 2018 when the data began to suggest that damage to the cornea was occurring in eyes with CyPass, potentially leading to a need for corneal replacement in the future. This stresses the need to monitor the safety and effectiveness of new (and old) procedures for glaucoma.
A final type of newer surgery involves placement of a tube-like device into the front chamber of the eye and leading aqueous humor to exit under the conjunctiva (XEN). The FDA approved XEN for use in the US and it was marketed in 2017. The most common method now being used to implant the device is to open the conjunctiva (similarly to trabeculectomy), and use a needle inserter to place it in the anterior eye chamber, tucking the other end back under the conjunctiva where aqueous would exit, forming a bleb. In general, the bleb is less visible than that after trabeculectomy. The procedure thus far does not require an iris opening to be made, but the entry into the eye is similar to trabeculectomy otherwise. There has been no direct comparison trial to trabeculectomy, in terms of pressure success. The device is made of porcine gelatin, so if you have religious beliefs that restrict you from having medical devices that are derived from pigs implanted in your body, you should have a conversation with your religious leader. It is presumed to have a lower rate of long-term infection, but no long-term data exist. Unlike trabeculectomy or tube-shunts, the pressure cannot be adjusted in the early postoperative period, as there are no adjustable sutures.
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