Glaucoma is usually treated successfully with medication to lower the pressure in the eye. If medication is not effective, laser and other surgical procedures may be of value in controlling the pressure and preventing further vision loss. Glaucoma tube surgery may be recommended if the pressure in your eye is uncontrolled. If left untreated it is very likely you will gradually lose vision in that eye.
What are aqueous shunts and what do they do?
Aqueous shunts are microsurgical drainage devices that help control the intraocular eye pressure (IOP) in glaucoma by creating a new drainage channel for the eye which results in a small blister or bleb behind the eyelid. Reducing the pressure on the optic nerve in this manner prevents further damage and further loss of vision in glaucoma.
Please note that control of the eye pressure with an aqueous shunt will not restore vision already lost from glaucoma.
There are many implants that can be used but the most common ones are Baerveldt implant, the Molten implant and the Ahmed glaucoma valve. They all consist of a small tube that takes the fluid from inside the eye (aqueous humour) to a plate underneath the outer coat of the eye (conjunctiva). The tube and bleb are mostly hidden under the eyelid.
Although all shunts perform approximately the same function, there are important differences that affect the eye pressure in the first few weeks after surgery and other differences that influence the healing of the eye around the shunt and the long-term eye pressure.
The Ahmed Glaucoma Valve contains a type of valve that helps to prevent very low eye pressure during the first few weeks after surgery. The Baerveldt and Molteno implants do not contain valves but do have other advantages. Because the Baerveldt and Molteno implants have no valve, they must be blocked with a stitch that is either tied around the outside of the silicone tube (external ligature), or threaded through the inside of the tube (occluding suture) at the time of surgery. The purpose of the stitches is to prevent the shunt from draining excessively in the first few weeks after surgery and causing the eye pressure to be too low.
On the outside of the eye
Initially after surgery the eye will be red and swollen to a variable degree. After major eye surgery the eyelid often droops. This normally resolves over a period of weeks to months. The aqueous shunt itself is not normally visible on the outside of the eye.
When the shunt is functioning normally, the drained fluid accumulates in a blister or bleb in the conjunctiva. The plate and its bleb are positioned far back behind the The plate portion of a shunt can be seen just underneath the eye surface when the eyelid is lifted. This fluid is slowly absorbed by the blood vessels on the eye surface.
A patch made of donor eye tissue, either from the sclera (the wall of the eye) or cornea (transparent tissue that forms the front of the eye) is often used to keep the shunt in place. This is the only part of the operation that might be visible after surgery.
Prior to surgery, you must continue all drops and tablets in accordance with your normal treatment regimen up until the morning of the operation. Blood thinning medications such as Aspirin, Warfarin and Clopidogrel should also be continued. We may ask you to stop taking blood thinning medication prior to surgery to ensure it is within the correct therapeutic range.
If you opt to have the surgery performed under general anaesthesia, a pre-operative assessment of your general health will be carried out prior to the surgery. Underlying medical conditions including cardiac disease, uncontrolled high blood pressure or diabetes will need to be addressed prior to scheduling of surgery.
The operation is usually carried out under general anaesthetic – you will be unconscious and not be aware during the operation.
- You can also have a local anaesthetic – in this case you will be awake during the operation. You will not be able to see what is happening, but you will be aware of a bright light. Just before the operation, you will be given an anaesthetic to numb the eye. You may be given intravenous sedation to help you relax.
- During the operation, if you are awake, you will be asked to keep your head still, and le as flat as possible. The operation normally takes an hour. A member of the team is usually available to hold your hand during the operation, if you want them to.
- At the end of the operation, a pad or shield may be put over the eye to protect it.
- To protect against a very low eye pressure in the early stages, a suture (stitch) is used to close the tube at the time of surgery. So in the early stages, before this suture dissolves (normally 5-6 weeks), the eye pressure may be high. This can be treated with drops or tablets.
The most obvious benefit of the surgery is to lower pressure inside your eye, help control pain and ultimately to prolong any useful vision. Your vision will not improve. Often the vision is temporarily worse as the level of pressure inside the eye stabilises. The benefit is long term (years), rather than immediate.
You should be aware there is a small risk of complications, either during or after the operation. In most cases the complications can be treated and in a small proportion of cases, further surgery may be needed. Very rarely some complications can result in loss of sight.
Sight may take several weeks to return to normal. Some patients will find their vision is not quite as sharp after surgery. The benefit is slowing (or stopping) the rate of deterioration caused by glaucoma. However, the operation cannot be totally guaranteed to stop the loss of vision in your eye. Eye surgery for any condition always carries a small risk that vision may be worse or that the eye may become blind after the operation.
There is a small chance the tube may rub on the inside of the cornea. This could cause the cornea to become cloudy (corneal oedema). This may require further surgery to reposition the tube end. Rarely in extreme cases, if significant corneal damage has occurred, a corneal transplant may be required
Very rarely, the eye pressure can drop too low or fall low too quickly. Low eye pressure is the biggest risk after the operation. Low eye pressure can result in bleeding at the back of the eye, which is a very severe complication. This is why it is important for you to attend your follow-up appointments as scheduled.
If your eye pressure is too low, we may need to inject some gel into the front of your eye and also recommend increasing or decreasing certain eye drops. Occasionally you may need another operation to reduce the amount of fluid draining through the tube.
There is a small chance of bleeding inside the eye immediately after surgery (called “suprachoroidal” haemorrhage). This may require further treatment, and may ultimately result in loss of sight.
There is a reasonable chance that a cataract (cloudy lens) may develop some years after surgery. This may require and operation
There is a small chance that double vision can occur after surgery. This may require a further operation.
There is a very small chance of infection inside the eye after surgery. This may require further treatment, and may ultimately result in loss of sight. if your eye becomes painful or red or the vision becomes blurred, you should seek immediate medical help.
Irritation (grittiness) or discomfort in the eye that may persist
The eyelid may become droopy on the side of the operation
There is a small chance that the tube can become exposed or erode (wear away) through the conjunctiva. If this happens further surgery is required to close the defect.
Aqueous shunt surgery has become more popular as a treatment for uncontrolled glaucoma in recent years partly because of improved safety, but also because success rates have improved.
There is a small chance that the tube will become blocked. This would require further surgery to unblock the tube.
The eye is normally padded after surgery and the eye pad is removed the following day.
If you have discomfort, we suggest that you take a pain reliever such as paracetamol every 4-6 hours (but not aspirin – this can cause bleeding). It is normal to feel itching, sticky eyelids and mild discomfort for a while after tube surgery.. Please don’t rub your eye.
You will be given eye drops to reduce pressure, inflammation, and to protect against infection. We will explain how and when to use them. After the operation, the inside of the eye is often inflamed (swollen). You will have anti-inflammatory drops to reduce this. The anti-inflammatory drops most commonly used in the hospital following aqueous shunt/tube is dexamethasone (Maxidex®). You may need to use them as often as every hour. We will give you specific instructions about this, as every patient is different. You will also have antibiotic drops. These drops are used to prevent infection following the operation, and usually you need to use them four times a day. The antibiotic drop most commonly used in the hospital following an aqueous shunt/tube is called chloramphenicol.
Certain symptoms could mean that you need prompt treatment, including:
- Excessive pain
- Loss of vision
- Increasing redness of the eye
Call us or attend your local eye casualty service immediately
After surgery the eye will be red and swollen to a variable degree at first. When the eye and the eyelid are in the normal position, the tube cannot be seen. You may be able to feel the device if you touch your upper lid.
The duration of time off work/school will depend on a number of factors such as the nature of the patient’s employment, the state of the vision in the other eye and the pressure in the operated eye.
Typically someone working in an office environment would require two weeks off, if the post-operative course is smooth. Someone whose occupation involves heavy manual work or work in a dusty environment may require a month or more (e.g. builders, farmers). This can be discussed with your consultant.
It is usually possible to restart contact lens wear around four weeks and sometimes sooner after aqueous shunt implantation.
Although it is safe to fly after surgery, patients should bear in mind that their surgeon will wish to see them for a number of post-operative visits to ensure that the tube is functioning properly and that the eye pressure is at the correct level.
In most cases, it takes two to three months for the eye to feel completely normal and sometimes longer in more complicated cases. At this point the patient will usually have a refraction (spectacle) test as the spectacle prescription may have changed slightly from the pre-surgery prescription.
It is important to avoid strenuous activity during the early post-operative period including swimming, tennis, jogging and contact sports.
It is permissible to watch television and read, as these will not harm the eye. For patients who wish to pray, it is better to kneel but not to bow the head down to the floor in the first two to three weeks. Bending over can cause significant pain when the eye is still inflamed after surgery. Similarly, activities such as yoga that require head-down posturing should be avoided.
As patients will be monitored closely following surgery it is recommended that they consult their doctor before commencing strenuous activity. If the eye pressure is very low after surgery the doctor may suggest refraining from all exertion and remaining sedentary until the pressure is restored.