Trabeculectomy

Take home points for trabeculectomy

Some patients want to know every detail of their surgery. So, we have made available videos of glaucoma surgery on the Glaucoma Center of Excellence website which is cited at the end of the book. Other patients only want to know the general principle of the operation: How does it work? Where do you do it? Will others be able to see where the surgery was done? We’ll cover those here.

Trabeculectomy means removing a piece of the trabecular meshwork. Similar operations have been done since 1900. Their general purpose is to let water leak from inside the eye, out through the wall of the eye and under the covering tissue (conjunctiva) where it slowly is absorbed. Peter Watson of England developed the concept of the present surgery in the 1960s and improvements have been added about every 5 years since then. To summarize what is done (Figure 23), the eye has two layers near the junction of the white and colored part: these are the conjunctiva, a flexible tissue a lot like sandwich wrap, and the sclera, the strong white part of the eye. The surgeon cuts and folds back the conjunctiva, makes an apron-shaped flap half-way down within the sclera, folds the flap back and removes tissue to make a hole into the front chamber of the eye. The iris would plug up this hole from the inside, so a piece of iris is removed right under the hole. The flap is put back and sewn in place with tiny nylon sutures that act to keep all the aqueous from running out immediately—this is essentially an adjustable valve. Then, the conjunctiva is sewn back in place to cover the area and to begin sopping up the fluid coming out, like a sponge.

Trabeculectomy Diagram
Figure 23: Trabeculectomy Diagram. Drawing illustrating trabeculectomy surgery. Upper drawing shows the conjunctiva is folded back and a flap is made in the sclera, part-way through. A hole is made into the eye (small dark oval under flap) and a piece of the iris is removed. In the lower drawing, the flap in the sclera and the conjunctiva are sewn back in place. The hole under the flap is shown as a dotted oval. 3 sutures are shown holding the scleral flap. These can be loosened after surgery to adjust the eye pressure.

The area of trabeculectomy is always under the upper eyelid – there’s room up there for 2 of them if the first one doesn’t work long enough. Most often other people can’t see where it was done, since it’s covered by the eyelid. It can be slightly elevated by the fluid coming out and it usually has fewer blood vessels than the surrounding conjunctiva, so it looks whiter there. Eye surgeons call this the bleb, since it looks something like a bubble (Figure 24). We tell patients it will be there, but often they forget and six months later they are startled to raise their eyelid and notice the bleb. My wife calls this the Saturday Morning I Just Noticed My Bleb Emergency Call. It’s always good to be able to reassure someone--the bleb is a success, not a problem.

Trabeculectomy Photograph
Figure 24: Trabeculectomy Photograph. Photograph of the area of trabeculectomy glaucoma surgery called the bleb (arrow). This is where fluid from inside the eye slowly comes out to keep the eye pressure lower. Most blebs are smaller than this example, which is shown so that the bleb can be more easily appreciated in a picture.

The trabeculectomy works when more aqueous fluid gets out of the eye and the new pressure is at or below the target (see section What is the target pressure?). This means we have to fool the body into thinking it healed the opening shut when it didn’t. Several things help to do this. One is how the flap is constructed. Another is that the eye’s own aqueous fluid actually prevents healing, for the same reason that the iris doesn’t heal shut an iridotomy made with the laser. Third, we often put a strong anti-healing medicine on the eye at the time of surgery to discourage the internal opening from closing—this is the drug mitomycin-C. Finally, the patient's part is to put anti-inflammation eye drops on every 2 hours for a couple weeks and then slowly taper that off, which is the final and important step in making the operation work by keeping the hole open.

Early after surgery, we want the pressure to stay a bit over the target. It helps to fool the eye into thinking nothing happened. So on the one day, one week, and three week visits (there are about four visits all together), you may hear that the pressure is still higher than the target. We plan that, and lower it into the target range gradually. Remember that the flap of sclera was sewn with stitches—these can be released or melted to reduce their tension, so aqueous flows faster through the hole and the pressure falls. Some surgeons use releasable sutures that are removed during a standard eye exam without any pain. My favorite is to melt them under the surface with a tiny laser delivery, one at a time.

We can tell a lot about how the operation is working during the first weeks, but I like to say that I’ll be able to tell you that we have a success in five years. By six to eight weeks, you’ll be stopping all eye drops to see if the target is achieved. I have patients whose trabeculectomy is still working 35 years later, so we’re in this for the long haul. Unfortunately, they all don’t work for three decades. About 20% of trabeculectomies fail to control pressure by one year. After that, about 2% stop working each year. In a review of trabeculectomies done at the Wilmer Glaucoma Center of Excellence, with lots of different patients, some with very difficult problems, over two-thirds were still at their target and on no medicine five years afterwards, and no further surgery had been needed for the eye.

The main issues that come up after trabeculectomy (other than pressure failure) are: too low a pressure (sometimes due to a leaking bleb), early or later infection, discomfort caused by the bleb area, and bleeding inside the eye. Low pressure can cause blurred or variable vision. When pressure is very low, the layers of the eye wall can fail to stay in their normal position. They drift off into the eye, causing dark shadows that block vision. These are called choroidal detachments and they do not harm the eye permanently. Another condition can occur when the pressure is low called hypotony maculopathy. In this, the back of the eye becomes slightly folded (like a balloon losing air), blurring vision. While these are uncommon events, they could lead to permanent changes in vision, so we treat to raise the pressure. Low pressure (hypotony) is fixed by removing the conjunctiva over the bleb, advancing the conjunctiva to cover the area, and restitching the flap back tightly. This is most often successful and in the vast majority, vision is improved and the target pressure is still achieved. Any operation can have bacteria enter the eye during surgery. These are most often the patient’s own bacteria that normally live on the eye’s surface. We take lots of steps to keep them out of the eye and to sterilize the eye surface just prior to surgery, but one in 3,000 glaucoma operations have an infection develop in the first month. We let patients know the signs of infection that they should look for. When they call us promptly about such symptoms, we are very successful at treating infection without bad results. In an infection, the eye has pain, a big increase in redness, a sticky discharge on the lids (pus), and vision often is much worse. Any two or three of these should lead to a fast phone call to the doctor, even on Saturday night.

Late infection can happen with trabeculectomy and to a lesser extent with tube-shunt surgery even months to years after surgery. Why this is true makes sense if you visualize the operation: it’s a new channel through the eye wall from the inside chamber, then under the flap, and finally under the conjunctiva. If bacteria can get through the first layer of conjunctiva, they can swim or drift inside the eye much easier than in a normal eye where the white sclera is intact. It’s obviously still hard for bacteria to get in, because among thousands of trabeculectomies, there are few infections. The rate is about one in 1000 operations each year after surgery. Again, one key to minimizing the risk of infection is to have patients recognize symptoms of infection and call in quickly. A bleb with an overt leak in the conjunctiva makes infection even easier--it’s a free ride into the eye from bacteria living around the eyelids and tears. Leaks are simple to repair, but require a return to the operating room.

For about a year after any surgery on any body part, the nerves in the area have to regrow and during that time things feel different. Most often this is minor and can be soothed by taking artificial tear drops (over the counter type). Many patients describe this as “it doesn’t quite feel like my old eye yet”. It is very uncommon for us to have to do surgery to fix these feelings, although occasionally the bleb gets too high or extends too far down all around the white of the eye and needs to be revised.

There are those for whom trabeculectomy works better and those in whom it’s unlikely to win. The success rate is higher in eyes without past surgery and in older persons. It’s like a senior discount: older persons heal worse, so the surgery works better. It's not so favorable if you scar a lot, have had other past eye surgery, or have ongoing inflammation in the eye or some form of secondary glaucoma. For reasons that aren’t fully understood, African-derived persons may do worse with trabeculectomy. (see section Special section for African-derived persons).

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