Aqueous Shunt Implantation is a procedure used to reduce the effects of glaucoma.
Aqueous humour is a fluid inside the eye that regulates IOP (intra-ocular pressure) and high IOP is the primary cause of glaucoma and other eye conditions. An aqueous shunt reduces the eye pressure by draining aqueous humour away safely – literally shunting it away.
The shunt used is a tiny silicone tube of less than 1mm in diameter that moves aqueous humour from inside the eye to an attached plate where it can drain away. The plate itself sits on the white of eye (the sclera) under the skin of the eye (conjunctiva) behind the eyelid: it’s not (usually) visible on the outside of the eye.
They are also known as tube implants, glaucoma tube shunts, glaucoma drainage devices, glaucoma drainage implants and setons: they are the same thing. There are two most commonly used types of aqueous shunt devices are the Ahmed Glaucoma Valve and the Baerveldt Glaucoma Implant pictured here (a third, known as the Molteno Implant, is used far less).
The Ahmed Glaucoma Valve has a valve to prevent low eye pressure for the first weeks after surgery, whereas the Baerveldt (and Molteno) implants don’t have valves so they are blocked with a stitch during surgery. These stitches prevent the shunt from draining excessively in the first few weeks after surgery and from causing the eye pressure to be too low.
The tube part of the shunt is placed inside the eye at the time of surgery and is so small that you can’t see it with the naked eye.
Aqueous shunt surgery usually takes one to two hours, and the patient is often under general anaesthesia, although local anaesthesia maybe be possible.
A patch made from tissue either from an eye bank (cornea or sclera) or from a commercial source (pericardium) is used to reinforce the eye surface over the outside of the shunt. These tissues do come from donors and are therefore tested to ensure that they cannot transmit certain infectious diseases such as Syphilis, Hepatitis B and C and HIV (the AIDS virus). They are not, as yet, tested for prion disease (Bovine Spongiform Encephalopathy or BSE, otherwise known as mad cow disease or v-CJD) as no suitable test exists. The risk of transmission of prion disease at present appears to be extremely low. Please note that after receiving donor tissue patients are no longer eligible to donate blood in the United Kingdom.
Patients are usually discharged home from hospital either the same day as the surgery or the following day, and there will need to be some followup care and clinic visits to ensure the procedure is as effective as possible. It can take several months for the eye to feel completely back to normal.
Mr. Gazzard will advise on which of the many options you have with surgical treatment is the best approach with your eye condition.
If you’d like to know more about whether this innovative treatment is an option for you, or think that you may benefit from a consultation, please get in touch here.