When medications or laser procedures fail to adequately control intraocular pressure (IOP), or if side effects prevent the continued use of medications, surgery becomes necessary to achieve the desired level of IOP. Surgery for glaucoma lowers IOP by either increasing the flow of fluid out of the eye or by decreasing the production of intraocular fluid.
It must be remembered that the optic nerve damage and subsequent loss of vision caused by glaucoma cannot be reversed. Thus, the point of surgery is not to improve vision, but rather to prevent further vision loss. Currently there is no glaucoma treatment that can restore vision already lost to the disease. For this reason, early diagnosis and treatment is vital. We recommend reading the section about glaucoma before continuing here.
This section describes canaloplasty, one of the latest surgical developments for the treatment of open angle glaucoma.
Click here to watch a video overview of canaloplasty. This video is provided by iScience Interventional, the company that manufactures the microcatheter used in the procedure. The video will open in a separate tab/window.
Traditionally, when non-surgical options have failed in the treatment of glaucoma, ophthalmologists have turned to filtering surgical procedures, such as trabeculectomy or drainage devices (see related chapters) to achieve better IOP control. And while trabeculectomy works quite well in most circumstances and remains the “gold standard” for glaucoma surgery, filtering procedures do require frequent post-operative visits and extensive use of post-operative medications. Furthermore, as with all surgical procedures, complications leading to visual loss can occur. For these reasons, alternatives have long been sought with the common goals of effective IOP lowering, simplified post-operative care, and reduced risk of complications.
Over the past decade a number of procedures have been devised to try to meet these objectives. Known collectively as non-penetrating glaucoma surgery, or NPGS, most of these procedures attempt to improve or re-establish the eye’s natural drainage system without the creation of a “bypass” and development of a post-operative bleb, as seen with traditional filtering surgeries.
Canaloplasty, the subject of this chapter, is a variation of a technique known as viscocanalostomy. In viscocanalostomy, the surgeon dissects deeply into the sclera, the white of the eye, near its border with the clear cornea. Just short of cutting into the inside of the eye, the surgeon stops and locates the cut ends of Schlemm’s canal, the beginning of the eye’s drainage system which encircles the cornea. A small canula, or tube, is used to inject a thick liquid into this canal, dilating and opening it, breaking up scar tissue and pushing out debris. In this manner the eye’s natural drainage pathways are opened and cleared, allowing better outflow of fluid from the eye.
Canaloplasty adds an additional step to this procedure with the aid of some remarkable technology. Using a tiny catheter, a flexible but strong tube with the thickness of a few human hairs, the surgeon passes a suture 360 degrees through Schlemm’s canal and then ties it tightly. The tension supplied by this suture functions like a stent in a blood vessel, serving to help keep the canal open long after the procedure. The presence of this stent suture appears to improve the long-term pressure lowering capability of the procedure.
A review of ocular anatomy may be helpful to better understand this procedure.
Canaloplasty is generally performed under local anesthesia- you will be awake but relaxed, and will experience no pain. After the skin around the eye is cleansed, a surgical drape is placed over the eye to maintain sterility. A small device known as a lid speculum is inserted in order to hold open the eyelids during the procedure. The eye is rotated downward, exposing the conjunctiva and sclera above the cornea, which is where the surgical site will be located. A small incision is made in the conjunctiva, which is then carefully lifted and separated from the sclera. A superficial flap of sclera is dissected up to the edge of the cornea. Next, inside the superficial flap, a deeper dissection is performed, nearly to full scleral thickness, and again is carried forward to the edge of the cornea. At this deep level the dissection will pass through Schlemm’s canal, the eye’s main drainage duct. Once this is found, the deeper flap of scleral tissue is cut away, leaving a space known as a ‘scleral lake’ where fluid will collect. A thick fluid called viscoelastic is then injected into each cut end of Schlemm’s canal to dilate it. An iScience micro-catheter is then passed into one cut end of the canal and retrieved from the other end. A stent suture is then tied to the catheter’s tip and the catheter is reversed back through Schlemm’s canal, pulling the suture along with it. The suture, now running completely around the entire canal, is tied tightly, keeping tension on the wall of the canal. The superficial flap of sclera is repositioned and sutured securely back into place, fully enclosing the surgical site. Finally, the conjunctiva is returned to its original position and sutured as well. Fluid can now more easily enter the fully opened drainage canals, resulting in lowered eye pressure.
Once surgery is completed, a patch is usually placed over the operated eye and worn for several hours. Pain or discomfort is generally mild. The first postoperative visit is performed the following day. The surgeon will check your vision, IOP, and the appearance of the eye. At this point instructions regarding acceptable levels of activity and use of postoperative eye drops, including antibiotics, will be given. Degree of activity, including ability to drive in the days following surgery, depends on each patient’s unique situation and must be judged individually. In general, strenuous activity, heavy lifting, and bending over should be avoided for the first few days.
Unlike filtering surgeries, such as trabeculectomy and drainage devices, canaloplasty is not dependent upon conjunctival healing and the development of a filtering bleb for its success. Therefore, excessive scar tissue leading to surgical failure is not typically a problem. Because the procedure does not enter the inside of the eye there is very little inflammation or swelling post-operatively, and almost zero risk of hypotony- intraocular pressure that is too low- as sometimes occurs with filtering surgery. Vision is typically only mildly blurred, and discomfort is minimal. Post-operative eye drop use and physician check-ups are less frequent than after filtering surgery. Follow-up visits may be scheduled every one to two weeks.
Canaloplasty is an effective procedure for IOP reduction, with recently published data indicating an average drop in IOP of 32% two years following surgery. This same study also found that the average number of required glaucoma medications decreased from 1.9 before to 0.5 following the procedure. This procedure is relatively new and good data is not yet available regarding long-term success rates. In some cases surgery fails to adequately control the IOP. Additional surgery may then be performed to reach the desired level of pressure within the eye. At such a point either a trabeculectomy or a drainage device procedure may be preferred (see sections on Trabeculectomy or Glaucoma Drainage Devices).
All surgical procedures carry some risk of complications. Some risks are common to all procedures and patients, and others are more specific to certain types of surgeries or to patients with particular conditions. A thorough explanation of complications will be provided with a surgical consent, should you choose to have surgery, and your physician will review the specific issues you may face based upon your unique circumstances.
Some potential complications of canaloplasty include, but are not limited to:
- Failure to adequately control IOP
- Bleeding within the eye (hyphema), usually mild and resolves within a week
- Low intraocular pressure (hypotony), much less common that with filtering surgery- noted in 0.5% of cases in one large study Infection within the eye (endophthalmitis)
- Loss of vision, extremely rare with this form of non-penetrating surgery
As with most diseases, there are a number of treatment options for glaucoma. As previously noted, surgery is usually considered when medications and laser trabeculoplasty have failed to adequately control IOP. Canaloplasty is not the only option available. Other surgical procedures may be considered based upon the type of glaucoma, condition of the eye, and level of IOP required. Some of these procedures are detailed in other sections of the library.
- Glaucoma drainage devices/tube shunts
- Laser cyclophotocoagulation
- Schlemm’s canal shunts
- Trabectome procedure
- Anterior chamber-suprachoroidal space filtration procedures