Colchester Eye Centre
Colchester Primary Care Centre
Tel: 07780 005 814
Monday to Friday, 9am to 5pm
Baerveldt aqueous shunt implants
What are aqueous shunt implants and what do they do?
Aqueous shunts are devices that are used to reduce the eye pressure in glaucoma by draining the fluid (aqueous humor) from inside the eye to a small blister or bleb behind the eyelid.
Reducing the pressure on the optic nerve in this way prevents further damage and further loss of vision in glaucoma.
It will not restore vision that has already been lost through glaucoma.
The aqueous humor is a fluid inside the eye and is not related to tears. Watering of the eye is caused by tears, not aqueous humor.
The aqueous shunt reduces eye pressure by draining aqueous humor.
The Baerveldt implant is made up of a small silicone tube (less than 1mm in diameter) attached to a plate. The tube takes aqueous humor from inside the eye and drains it to the plate which sits on the white of the eye (sclera).
The plate sits under the skin of the eye (conjunctiva), behind the eyelid.
Because the Baerveldt implant has no valve, it must be blocked with a stitch that is either tied around the outside of the silicone tube or threaded through the inside of the tube at the same time of surgery or both.
The purpose of the stitch is to prevent the shunt from draining too much in the first few weeks after surgery and causing the eye pressure to be too low.
Will the implant affect the appearance of my eye?
Initially after surgery the eye will be red and swollen to some degree.
After major eye surgery the eyelid often droops, but this will recover over a period of weeks or months.
The implant itself is not normally visible on the outside of the eye.
When the implant 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 eyelid so they cannot usually be seen. This fluid is slowly absorbed by the blood vessels on the eye surface.
Occasionally, the implant or bleb can be seen in extremes of gaze, when the eye is looking very far down and in.
A patch of donor tissue is often used to keep the shunt in place and this is the only part of the operation that may be visible after surgery.
The tube part of the implant is placed inside the eye at the time of surgery. This is very small and usually cannot be seen with the naked eye. The tube itself is made of transparent silicone. The length
of the tube inside the eye is usually 1 to 2mm.
Medication prior to surgery
Prior to undergoing surgery, patients are asked to continue all drops and tablets as normal up until the day of the operation.
Blood thinning medications such as aspirin, warfarin and clopidogrel should be continued. Patients who are taking warfarin are advised to have their INR level checked at least two weeks prior to surgery to ensure it is within the correct therapeutic range.
Implant surgery usually lasts 1 to 2 hours (or three hours in extreme cases).
Baerveldt implant surgery is generally done under local anaesthetic. The eye will be anaesthetised first with eye drops and then an injection of anaesthetic will be given around the eye. The anaesthetic injection itself may cause some mild discomfort; a slight sensation of pressure as the anaesthetic is delivered. The injection anaesthetises the eye, preventing not only pain but also excessive movement during surgery.
During surgery patients are covered by a sterile sheet, or drape, which keeps the operation site sterile and also prevents patients from seeing any of the surgery.
Patients will be aware of the surgeon working around the eyes; but this should not be painful.
During the surgery, Mitomycin C may be applied to the surface of the eye for a brief period of time (up to five minutes). Mitomycin C is a drug that was originally used to treat cancer, but is also used in glaucoma surgery to reduce scarring. Scarring prevents the implant from functioning in the long term, as it prevents the aqueous humor from being absorbed back into circulation.
The Mitomycin C is then washed away from the eye with sterile water so that no residual drug remains.
A patch made from tissue either from an eye bank (cornea or sclera) or from a commercial source (pericardium) is used to prevent break down of the conjunctival surface tissue over the shunt.
If donor tissue is not used, breakdown of the conjunctival surface of the eye over the implant can occur in 10% to 14% of cases. When donor tissue is used the risk of breakdown is less than 3%.
The donor tissue used in aqueous shunt surgery is not live transplants. It is simply used to reinforce the eye surface over the outside of the shunt. The tissues comes from donors and is tested to ensure it cannot transmit certain infectious diseases such as syphilis, hepatitis B and C and HIV (the AIDS virus).
Please note that after receiving donor tissue patients are no longer eligible to donate blood in the UK.
After surgery – post-operative care
The day of surgery and the next day
Patients are usually discharged home from hospital either the same day as the surgery or the following day.
It is important for the eye to be examined again one day after surgery or within 48 hours.
The eye is normally padded after surgery and the eye pad is removed the following day or day after.
If the un-operated eye does not see well, then the operated eye will not be padded. Instead, a clear shield will be placed over the operated eye so that it is still possible to see after surgery.
Patients are advised to ask a friend or relative to accompany them home after surgery, especially patients who have poor sight in the un-operated eye.
Eye drops will be prescribed to use regularly after surgery. These are started on the day after surgery, after the post-operative examination. It is not usually necessary to use eye drops the first night after the surgery.
It is important that any eye drops for the un-operated eye are continued unless you are advised otherwise.
Patients are given a supply of postoperative eye drops on leaving the hospital; these should last one
month. The post-operative eye drops will normally need to be taken for 2–3 months. Patients are advised at each post-operative visit whether a change in the dosage of drops is required. The drops should not be stopped or the dosage changed without consulting the doctor.
Post-operative clinic visits
Patients are usually seen once a week for the first four weeks, and may be seen more frequently if the eye pressure is either too high or too low.
High pressure after surgery
In some cases, the stitch may cause high pressure after surgery. This can be removed, usually 2–3 weeks after the surgery at which point the pressure drops. This procedure is very quick, painless and is performed in the outpatients clinic or in the eye theatre.
It is important to note that this stitch has an important purpose; to protect the eye from the effects of low pressure in the first few weeks after surgery.
If the pressure is high in the first weeks after surgery this does not mean that the shunt will not work, but simply that the shunt is not working yet. In such cases, it is normal for the shunt to start working after the stitch had been removed.
Low pressure after surgery
Sometimes the pressure may be too low after surgery and this can in rare cases be dangerous.
Although very low pressure is often painless, it may be associated with a dull aching feeling or a throbbing sensation within the operated eye.
Low pressure, when it occurs, is usually detected during clinic appointments and is often remedied by stopping any pressure-lowering eye drops and by reducing steroid eye drops. Sometimes an injection of a jelly material (viscoelastic) is required to raise the pressure. Occasionally, a further operation is
needed to reduce the drainage from the tube.
Activity after surgery
During the early post-operative period it is important to avoid strenuous activity including swimming, tennis, jogging and contact sports.
It is safe to watch television and read, as these will not harm the eye.
Bending over can cause significant pain when the eye is still inflamed after surgery. For patients who wish to pray, it is better to kneel but not to bow the head down to the floor for the first 2–3 weeks. Similarly, activities such as yoga that require head-down posturing should be avoided.
When can I go back to work?
The length of time off work will depend on a number of factors such as the nature of your 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. Someone whose occupation involves heavy manual work or work in a dusty environment may require a month or more.
Most glaucoma surgical studies examine success rates over a five-year period.
With an aqueous shunt such as the Baerveldt, the expected success rate over five years is now between 70% and 80%. Although a sizeable proportion of patients achieve good pressure control without the need for continued glaucoma medication, many patients still require some medication to assist the shunt in controlling the pressure. In such circumstance, the medication required is usually less than what was required before the surgery.
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.
Severe complications are uncommon but are most likely to happen if the eye pressure drops very low or very quickly in the early postoperative period.
A very low or an abrupt drop in eye pressure is rare, but can result in severe bleeding at the back of the eye (less than 1%).
The risk of serious infection inside the eye from aqueous shunt surgery is also rare (less than 1%).
There is also a small long-term risk that the tube implant will develop a blockage (requiring further surgery to unblock the tube); It may also erode or rub against the cornea and require further surgery to move the tube so it does not rub. In extreme cases, where significant corneal damage has occurred, a corneal transplant may be required.
Out of hours (weekdays 5pm to 7pm and weekends and public holidays, 11am to 4pm), please telephone 01206 286 882, or contact your GP, urgent treatment centre or your nearest accident and emergency department or visit the NHS 111 website or the All About Vision website.
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