TRABECULECTOMY FOR GLAUCOMA
Glaucoma is the name for a group of eye conditions which cause damage to the optic nerve at the back of the eye. The naturally made fluid in the eye is unable to drain away properly which can result in a build up of pressure within the eye. The pressure is usually treated with eye drops. If the eye drops fail to reduce the pressure, damage to the optic nerve will cause permanent loss of sight. To lower the eye pressure a surgical procedure known as a trabeculectomy can be carried out.
What does Trabeculectomy involve?
A small opening is made in the white part of the eye near the upper eyelid to form a drainage channel. The opening allows the eye fluid to drain away to a reservoir known as a filtering bleb and reduce the eye pressure. The bleb is formed during surgery from the normal covering of the eye. The bleb will have the appearance of a bubble like bump on the white of the eye, usually under the upper eyelid. A strong antiscarring drug (Mitomycin C) may be used to improve the success of the operation.
A trabeculectomy can take up to an hour and can be carried out most often with a local anaesthetic. It can also be performed under general anaesthetic. The doctor will discuss which option is most suited to you.
After a successful trabeculectomy it may be possible to reduce glaucoma eye drops. If the trabeculectomy is not successful the operation may need to be repeated or further treatment may be required. The aim of the operation is to reduce the risk of further
damage to the optic nerve. It is not aimed to improve your sight, but will hopefully help protect your vision in the longer term.
How eye pressure is controlled by trabeculectomy?
The opening for fluid to drain out is covered by a valve like flap of tissue. The tightness of this valve is controlled by 3 to 4 very fine stiches. The tighter the stiches the less fluid is allowed to flow out of the eye. Often your surgeon would leave the stiches slightly tighter at the start to avoid a precipitous drop in eye pressure following the trabeculectomy operation. The stiches are then gradually loosened or removed after the operation to allow more fluid to flow out of the eye. This will enable the eye pressure decrease to the desired level (5-12 mmHg) slowly over the first post operative month.
During the procedure
Trabeculectomy generally take 45 minutes. Trabeculectomy surgery under local anaesthetic is not painful although you may feel a sensation of pressure in the eye at some stages during the operation. A sterile cover will be placed over your face and the other eye to keep the area clean, but it will be kept clear from your nose and mouth by a stand with circulates fresh air. Your eye will be kept open using a special instrument, so you don’t have to worry about keeping the eye open yourself. It is important that you don’t move suddenly during the operation. The bright microscope light prevents you from seeing what is going on and many patients see whorls of blue or purple light during the operation. The surgeon will discuss the way to communicate with him/her: you may choose to hold a nurse’s hand which you can squeeze if you need to communicate with the surgeon. If you feel you need to cough or sneeze you can tell us this, but take care not to move your head until the surgeon says it is safe to do so.
What are the risks?
Some of the risks involved are:
• For a period of time pressure in the eye may become too high or too low. If eye pressure is too high, your surgeon will help you reduce pressure with adjustment or removal of stiches. If eye pressure is too low (<5 mmHg), then often your surgeon would manage with conservative methods first but occasionally will require return to theatre for injection of a material that can improve eye pressure.
• In some cases a cataract may develop (~10%). This can be treated by an operation if necessary.
• Serious complications are rare, but very occasionally the sight can get worse after the trabeculectomy and not recover.