Baerveldt or Ahmed valve & patch graft


This page gives you information that will help you decide whether to have an aqueous tube operation. You might want to discuss it with a relative or carer. We hope this information is sufficient to help you decide whether to go ahead with the recommended treatment.

baerveldt tube
Baerveldt tube
Why would you want to have this procedure?

Your eye surgeon has recommended a tube operation because medical treatments (drops), or other previous surgery have not controlled your condition adequately, or when drop treatment is unsuitable. In some cases it may even be used as the first choice of treatment.  The decision to operate is made by the doctor after assessing your individual progress and condition.

It is important to remember that this procedure is performed to save the sight you still have. It will not restore any sight you may have already lost; neither will it improve your sight.

The procedure

You will attend the day ward for approximately a whole day. Occasionally it may be necessary to stay overnight, but this is not the normal practice. The treatment will be performed in operating theatres. You will need to fast (no food or water) for six hours before the surgery time if your operation is under general anaesthetic or sedation.

Ahmed valve
Ahmed valve

It is important that you use your regular eye medication drops as normal on the morning of your operation, unless your doctor has told you otherwise.

An Aqueous Shunt/Tube is an operation that involves surgically inserting a small silicone tube (less than 1 mm in diameter) into the front chamber of the eye. The tube aims to drain the excess fluid within the eye to a plate just under the outer surface of the eye, between the sclera (white wall of the eye) and the conjunctiva (clear outer skin of the eye surface). By draining away the excess fluid inside the eye, the amount of pressure within the eye is reduced. The plate is positioned towards the back of the eye and forms a small blister or ‘bleb’ where the fluid is drained to. You cannot see the bleb as it is positioned too far back behind the eye to see. The tube that sits inside the front chamber of the eye is also very small, and you need a microscope to see it. The bleb and tube do not cause any feeling or sensation, and you cannot feel the fluid flowing through the tube.

The tube operation usually takes around one to two hours, and is usually performed under a general anaesthetic, (you will be asleep).

To stop the tube from moving around and becoming exposed through the conjunctiva, a patch made from donor cornea or sclera is usually stitched onto the surface of the eye, over the tube. The donor tissue has always been tested for infections such as Hepatitis B and C, Syphilis and HIV. A test for v-CJD (Mad cow disease) has not yet been designed, but the risk of transmission appears to be extremely low.
After the operation

You will be seen in the clinic the following day make sure the operation is working well.

It is vital that you attend the clinic follow-up visits as requested, as in the initial period following the operation it is necessary to frequently check that it is working well and there are no complications. You may have to attend the clinic every week or two for the first four weeks after the operation. The frequency of visits will be gradually reduced after this. Your doctor will decide exactly how often you need to be seen, as every patient is different.

If you are using glaucoma drops, these will usually be stopped to the operated eye after the operation. If you continue to use them, the eye pressure could drop too low, and this can be dangerous. Please check with the nurse or the doctor whether or not you need to continue using them if you are unsure.

If you are using glaucoma drops to the untreated eye, please continue to use them unless clearly instructed otherwise.

Your eye is normally patched before you are discharged from hospital, and is removed the following day.

If the un-operated eye has poor vision, then the operated eye will only have a clear shield over it, so that you can still see after the surgery to move around.

After the operation, it is usual for the eye to be a little red and swollen, and feel a little uncomfortable. Some patients are aware of the tiny stitches which are used for the operation. Although uncomfortable, these symptoms are not serious, and will get better over the first few weeks to months.

It is not uncommon for the operated eye to be a little sticky in the mornings. The eyelids can be gently cleaned with boiled, cooled water. Please speak to your doctor for instructions about this.

Occasionally the eyelid may droop, but will resolve itself slowly over a few weeks.

As with any operation, the affected part of the eye will take a little time to settle back to normal. It is normal that some patients find their vision is blurred. This may fluctuate from day to day for some weeks to months. Once the eye has settled, a visit to your optometrist/optician for new glasses will usually improve your sight to very similar, if not the same as it was before the operation. You doctor will inform you when the right time for a glasses check is – usually around 3 months post op.


After the operation, the inside of the eye is often inflamed, and you will be given anti-inflammatory drops to reduce this. How often this drop is used will vary for each patient, and may need to be used as frequently as every hour. You will be given specific instructions. The anti-inflammatory drops most commonly used in the hospital following trabeculectomy is Dexamethasone (Maxidex).

You will also be given antibiotic drops. These drops are used to prevent infection following the operation, and are usually used four times a day. The antibiotic drop most commonly used in this hospital following trabeculectomy is called chloramphenicol.

You will also be given a plastic shield to wear at night. This is to prevent you accidentally rubbing your eye during the night. The shield should be worn for four weeks following the operation, unless otherwise instructed. The shield should be washed and thoroughly dried before covering the eye each night. You may also wear it during the day if you are concerned.

The pressure in the operated eye may still have high pressure for the first few weeks after the surgery and sometimes may require another small operation to ‘adjust the suture’ around 2-3 months later in order to lower the pressure.

Complications after tube surgery

Occasionally your vision may not be as sharp after the operation as before it, even with new glasses. It can be upsetting if your sight seems worse, but if this operation has been suggested, it is because the doctor considers you are in danger of losing your sight altogether if the glaucoma is left uncontrolled.

Infection is a complication that can occur after any operation, and serious infection is uncommon. However, certain symptoms could mean that you need prompt treatment, including:

If you experience any of these symptoms telephone the Kersley Eye Clinic for advice immediately. Or visit your nearest accident and emergency (A&E) department. It is vital that these symptoms are treated immediately as they could lead to loss of sight.

Pressure drop

Very rarely, the pressure within the eye can drop too low, or fall low too quickly. If this occurs, further surgery may be needed. Surgery might include increasing or decreasing certain eye drops, or injecting some gel into the front of the eye. Occasionally another operation is required to reduce the amount of fluid draining through the tube.

Low eye pressure is the biggest risk in the early post-operative period, which is why it is important to attend your follow-up appointments as scheduled. Low eye pressure can result in bleeding at the back of the eye, which is a very severe complication.

Activity following tube surgery

You should avoid strenuous activity during the post-operative period. Swimming and contact sports should also be avoided. It is safe to watch TV and read as normal.

If you are working, you should arrange to be away from work for approximately two weeks, but this can depend on the nature of your employment, and the level of vision in the other eye. It is possible to require longer time off if you do heavy manual, or dirty/dusty work.

In the long term, if you plan to travel abroad, you should let your doctor know as it is advisable to take an adequate supply of drops with you. You should check with the eye doctor before travelling.

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Kersley Eye Clinic Harley Street London

The Kersley London Eye Clinic provides Ophthalmic Services and Contact Lens in Harley Street Central London.


Mon-Fri: 9.00a.m-5.00p.m
Sat-Sun: Closed

42 Harley Street, London W1G 9PR, UK

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