Traditional Glaucoma Surgery
Trabeculectomy is an operation which lowers the eye or intraocular pressure (IOP) within the eye to help preserve vision. Any vision lost due to glaucoma cannot be restored.
For patients with glaucoma, the drainage of fluid from within the eye (aqueous humor) is impaired resulting in a raised intraocular pressure which frequently results in the development of glaucoma. The surgery works by draining aqueous humor from within the eye, through a trap-door into a reservoir or bleb (figure 10) to lower the intraocular pressure.
It is important to remember that the aqueous humor is fluid within the eye and is not related to the tears which cause the eye to water.
The main benefit of Trabeculectomy is the reduction of the pressure within your eye which in turn will help to pressure your remaining sight.
The operation is either performed under local anaesthetic with sedation or under general anaesthesia. If you are having local anaesthetic with sedation, an injection of anaesthesia is given around the eye (which may sting and or feel like pressure around the eye) and then medicine to sedate you will be given.
The operation involves opening the skin of the eye (conjunctiva) under the upper lid to expose the wall of the eye (sclera). A trap-door is made in the sclera and then a small hole is made in the remaining sclera beneath. The trap-door is sutured (stitched) with releasable sutures to prevent aqueous humor (fluid within the eye) from draining out of the eye too quickly. These sutures if required can then be removed (releasable sutures) in clinic after the surgery should the IOP be too high.
The skin of the eye (conjunctiva) is then replaced over the trap door in its original position and secured with sutures which are often removed in clinic if they are not buried in the conjunctiva. The whole operation site is covered by the upper eyelid (figure 11).
Figure 11 – Cross section of the front of the eye, showing the ‘trap door’ opening made in the sclera (wall of the eye). Source: National eye institute media library
After the surgery, a clear shield will need to be work at night for the first 2 week. You should avoid any strenuous activity for the first 4 weeks. As a general rule, you will require 2 weeks off work however, this may be longer depending on your profession. As you will need to be seen frequently following your surgery, avoid booking travel arrangement for the first 3 months following surgery.
The eye will usually appear red or blood shot for the first 3-4 weeks following the operation.
Your vision may be blurred following the surgery due to the eye drops used and from the surgery itself. The vision will improve however, a change of glasses prescription may be required to fully correct your vision.
All glaucoma drops to the OPERATED eye and acetazolamide (if being used) will be stopped after surgery. Instead you will be an anti-inflammatory, anti-biotic, and a pupil dilating drop to be used regularly.
It is important that, your drops to the UNOPERATED continue.
Initially, you will be seen every week for the first four week and then fortnightly for the next four weeks. If you have a complication from the operation then you may need to be seen more frequently.
Your vision is usually more blurred after the operation and may take several weeks to return to normal. Some patients will find that their vision is not quite as sharp after surgery. The vision generally stablises at around 3 months when you should see you optician for a glasses test. It is important to remember than any vision lost due to glaucoma cannot be restored by surgery.
High or low eye pressure
Your IOP may be high or low following surgery. If your IOP is high then, depending on how many weeks you are following the operation, either massage will be used to bring your eye pressure down (usually first week following surgery) or remove a suture (releasable suture) on your trabeculectomy. Your eye pressure will then be rechecked.
Infrequently, your IOP may be too low and you will need to be watched more closely with more frequent visits. If the low IOP is causing a reduction in vision or swelling at the back of the eye then you may need either a small injection of jelly into the eye or another operation to reduce drainage out of the trap-door by placing more sutures on the trap door.
There is a reasonable chance that a cataract (cloudy lens) may develop some years after surgery. This may require an operation.
Irritation, grittiness or discomfort is common after the operation and settles down within the first four weeks.
Your eyelid may become droopy on the side of operation after surgery. This usually settles down and the eyelid position returns to normal / near normal. Rarely if the eyelid is still droopy after 3 months then you may need a small operation to lift the eyelid to match the other eye.
Loss of vision
Rarely (about 1:1000) patient develop blindness from the operation due to bleeding or infection of the eye.
The aqueous shunt also known as a tube shunt or glaucoma drainage device, is made of silicone and consists of a thin tube (less than 1mm in diameter) attached to a plate. The tube drains fluid (aqueous humor) out of the eye onto the plate which sits under the “skin layers” of the eye (Conjunctiva and tenons).
There are several types of aqueous shunts however, the commonest types are the Baerveldt tube, Paul tube and the Ahmed valve.
The aqueous shunt works to lower your intraocular pressure by draining fluid (aqueous humor) out of your eye.
The main benefit is to lower your eye pressure to preserve your existing sight and prevent further sight loss from glaucoma. It will not improve or reverse the sight already lost to glaucoma.
At 5 years following surgery, the success rate is up to 80%. However, although a number of patients are able to stop drops, many patients still required glaucoma drops (albeit fewer than before the operation) to keep the intraocular pressure controlled.
The operation is usually performed under general anesthesia as the operation can take up to 90 to 120 minutes. Occasionally, if following a medical assessment, it is felt that general anesthesia will put you at risk, the operation can be performed under local anaesthesia with sedation.
The aqueous shunt, for the majority of patients is placed under tissues in the region of the eye under the upper lid. During the operation, again in the majority of patients, anti-scarring medication called Mitomycin C is applied to the eye to for a few minutes and then washed away.
In terms of the surgery, in brief, the skin of the eye is opened, the plate of the aqueous shunt is the fixed to the wall of the eye (sclera) with non-dissolving stitches and the tube is then placed into the front chamber of the eye. To prevent the shunt from draining too much fluid out of your initially a stent is placed inside the tube which can be removed at a later date with a minor operation. Sometimes if despite the stent the shunt is draining too much fluid out of your eye, a stitch is placed around the tube which can be lasered open at a later date in the clinic. The finally part of the surgery involves placing a patch of tissue over the tube to prevent the tissue breaking down over the tube and the closing the skin of the eye. A pad and shield are then placed over your eye.
You will usually be discharge on the same day as your operation once your eye pressure has been checked.
The eye will look red and blood shot and feel gritty for the first 2-3 weeks after the surgery. During this period your vision may also be blurred. These symptoms gradually improve over the first 6 weeks after the operation.
The pad and shield should be removed the day following your operation and the drops prescribed should be commenced.
All glaucoma drops to the OPERATED eye and acetazolamide (if being used) will be stopped after surgery. Instead you will be an anti-inflammatory, anti-biotic, and a pupil dilating drop to be used regularly. If your eye pressure goes up initially a glaucoma drop will be restarted.
It is important that, your drops to the UNOPERATED continue.
You will be seen before you go home on the day of surgery and sometimes the following day. Patient are then usually seen 1 week later and then further following is decided based on the eye pressure and examination findings.
During the operation, to prevent the aqueous shunt from over-draining fluid from within the eye and thereby causing the eye pressure to go very low, a stent is placed inside the tube and sometimes a stitch is also placed around the tube.
After the operation, if the intraocular pressure is not low enough, the stitch around the tube can be lasered in the outpatient clinic. If after 6-8 weeks, the intraocular pressure is still not low enough then the stent is either partially or totally removed either in the clinic or in the operating theatre.
Five year published data suggest that the risk of complications overall is the same for the Baerveldt tube and Ahmed valve. However, below are the main risks of surgery:
Low pressure – If too much fluid is passing through the tube then the pressure can go very low. If this occurs, your vision may become blurred and you may experience discomfort in your eye. Low pressure increases the risk of a major bleed inside of the eye called a suprachoroidal haemorrhage which occurs in less than 1% of patients. To treat the low IOP it may be necessary to inject a gel into the eye and if this fails, to take you back to operating theatre to place a stitch around your tube to reduce the flow.
Infection – Infection inside the eye can be a devastating but rare (approximately 1 in 1000) complication of any eye operation and can result in sight loss
Bleeding – Bleeding is a risk with any operation. Bleeding in the front chamber of your eye usually stops on its own. Bleeding at the back of the eye (suprachoroidal haemorrhage) which can occur in less than 1% of patients can be much more dangerous and can result in complete loss of vision. The main risk factor for this happening is when the pressure is very low in the eye.
Double vision – Due to the size of the tube implant and its position near to the muscles that control eye movement, it is possible that it can affect your eye movements resulting in double vision in 2-5% of patients.
Cosmetic effect – Very occasionally the tube, patch graft or drainage reservoir can be seen on the surface of the eye. This is often only when the eye is looking into the extremes of gaze. Care is taken to make these areas hidden under your eyelid, but in some circumstances the tube surgery may be visible.
Erosion of the tube to the surface of the eye – Although a patch of tissue is used during the operation to protect the tube, erosion (where the skin of the eye or conjunctiva breaks down) remains a small risk (2-4%). If this occurs you will require an operation to repair the breakdown.
Damage to the cornea – Sometimes the tube can rub against the inside surface of the cornea, which may cause the cornea to become cloudy. Usually this will be spotted by your glaucoma specialist before it becomes a problem and the tube can be re-positioned with a minor operation. Sometimes the cornea can become cloudy even if the tube is well placed. At 5 years, clouding of the cornea has been reported to occur in up to 12% of patient undergoing any tube surgery. If the cornea remains cloudy then you may need to see a corneal specialist.
Blurred vision – Your vision will be blurred after the operation and should improve gradually over a period of several weeks back to its usual level.
Cataract (clouding of the lens in your eye) – If you have already had cataract surgery then this will not be an issue. If you have some cataract, then we may operate on this before your tube surgery. If you have no significant cataract before the operation then the surgery may cause cataract to form earlier than it would have done otherwise
Failure – At 5 years, the published failure rate was 53% in the Ahmed valve group and 40% for the Baerveldt tube.
Droopy eyelid – After any type of eye surgery, the upper eyelid may droop down towards the pupil. This is usually a temporary problem that resolves within a few weeks to months.