Glaucoma Surgery

When medicines and laser surgeries do not lower eye pressure adequately, doctors may recommend a procedure called filtering microsurgery known as a trabeculectomy or an Ahmed Valve.


In filtering microsurgery, a tiny drainage hole is made in the sclera (the white part of the eye) in a procedure called a trabeculectomy or a sclerostomy. The new drainage hole allows fluid to flow out of the eye and helps lower eye pressure. This prevents or reduces damage to the optic nerve.(1)


Angle Closure Glaucoma

Is There Pain During the Surgery?

In most cases, there is no pain involved. The surgery is usually done with a local anesthetic and relaxing medications. Often a limited type of anesthesia, called intravenous (I.V.) sedation, is used.

In addition, an injection is given around or behind the eye to prevent eye movement. This injection is not painful when I.V. sedation is used first. The patient will be relaxed and drowsy and will not experience any pain during surgery.

Success Rate

Most of the related studies document follow-up for a one year period. In those reports, it shows that in older patients, glaucoma filtering surgery is successful in about 70-90% of cases, for at least one year.

Occasionally, the surgically-created drainage hole begins to close and the pressure rises again. This happens because the body tries to heal the new opening in the eye, as if the opening were an injury. This rapid healing occurs most often in younger people, because they have a stronger healing system. Anti-wound healing drugs, such as mitomycin-C and 5-FU, help slow down the healing of the opening. If needed, glaucoma filtering surgery can be done a number of times in the same eye.

Outpatient Procedure

Usually, filtering surgery is an outpatient procedure, requiring no overnight hospital stay. Within a few days after surgery, the eye doctor will need to check on the eye pressure. The doctor will also look for any signs of infection or increase in inflammation.

Recovery Time

For at least two weeks after surgery, patients are advised to keep water out of the eye. Most daily activities can be done, however, it is important to avoid driving, reading, bending, and doing any heavy lifting for a minimum 6 weeks.
Each case is different, so check with your doctor for specific advice.

Appearance of the Eye after Surgery

The eye will be red and irritated shortly after surgery, and there may be increased eye tearing or watering. The inner eye fluid flows through the surgically-created hole and forms a small blister-like bump called a bleb. The bleb, usually located on the upper surface of the eye, is covered by the eyelid, and is usually not visible.

Ahmed Valve

Also known as "aqueous shunts" or "glaucoma drainage devices," we'll refer to them simply as "implants."(2)

Ahmed Valve

The idea behind implants is to enhance standard glaucoma surgery by positioning a device that will help keep the surgically-created drainage opening from healing and closing down. Many current implants include a tube through which the aqueous fluid passes. Others are solid and promote the flow of fluid along the surface of the implant.

Regardless of the type, all implants have a common goal - to decrease IOP by increasing outflow of fluid from your eye. Implants used for glaucoma evolved from the Molteno glaucoma implant, first tested in 1969. Since that time, many other implants have been designed. The two basic types are "valved" (Ahmed or Krupin) and "non-valved" (Molteno, Baerveldt) designs.

When Implants Are Used

It is estimated that several thousand implants are used in the USA each year. Most of these are performed on what eye surgeons think of as "complicated glaucomas." Glaucoma implants may be considered in forms of glaucoma following injuries to the eye.
They are also used in cases of congenital glaucoma where other surgeries have not worked, and in cases of neovascular glaucoma (a type of glaucoma often associated with diabetes, characterized by blood vessels that grow across the iris and drainage area, closing off fluid outflow). Implants may also be used when other glaucoma treatments have not been successful.

Implant Surgery

In conventional surgery, a tiny drainage hole is made in the sclera (the white part of the eye). This procedure is known as trabeculectomy or sclerostomy. This opening allows fluid to drain out of the eye under the delicate membrane covering the eyeball known as the conjunctiva. Locally applied medications or injections may be used to help keep the hole open.

With implant surgery, most of the device is positioned on the outside of the eye (toward the back as shown in the drawing) under the conjunctiva. A small tube or filament is carefully inserted into the front chamber of the eye, just in front of the iris (colored part of the eye). The fluid drains through the tube, or along the filament, into the area around the back end of the implant. The fluid collects here and is reabsorbed.

Complications and Successes

Since the implant is a foreign body, there is often an inflammatory reaction immediately after surgery. This is commonly associated with a rise in IOP, and usually stabilizes within four to six weeks. IOP levels seldom stabilize below the mid-teens after implant surgery even when medications are added to the treatment plan.
The success of implants and length of time they are effective appear to be related to the amount of surface area covered by the implant for drainage. The larger the implant surface, the greater the likelihood of success. However, there are tradeoffs. With increased size comes a greater chance of complications. There is the possibility of IOP being too low. This is known as "hypotony." The implant may also interfere with the external muscles that move the eye from side to side.
Implants are sometimes used after other surgeries have failed, most often due to healing and scarring over of the surgical opening. When this happens, eye pressures return to the higher, pre-surgery levels.