Aqueous Shunt Surgery

Aqueous shunt implantation is a microsurgical operation where the eye surgeon places a tiny silicone tube-like device (variously referred to as “glaucoma tube shunts or implants” or “glaucoma drainage devices or implants” or “setons”) in an area towards the back of the eye.

When the device is functioning normally, it drains the excess fluid inside the eye, thus reducing the pressure inside your eye. The fluid forms a so-called “bleb” which is a small permanent blister-like swelling on the surface of the eye, typically hidden under the eyelid so as it is not usually visible to you. The fluid in the “bleb” is absorbed back into the blood stream, and does not leak onto the surface of the eye.

The IOP is closely monitored during the very important postoperative clinic visits and important interventions may need to be done, depending on the IOP found on assessment at the follow-up clinic.

Aqueous shunt implantation helps preserve sight in people with glaucoma by producing a controlled escape of eye fluid so reducing the raised IOP.

The “bleb”, the area of surgery typically under the eyelid, is not usually visible except on the closest inspection.

In the majority of patients, an aqueous shunt implantation will achieve a low IOP for years: between 70 to 80% were still successful after 5 years in studies. A sizeable proportion of these do not need to use additional glaucoma medication. However, many patients do have to supplement the shunt operation with the use of glaucoma medication to control the IOP, but the medication now required is usually less than that required before the surgery.

After surgery, common short term effects are a red inflamed & swollen eye, the eye feels a little uncomfortable, and drooping of the eyelid. These effects typically resolve over some weeks or months.

Sometimes your vision may be less sharp than before surgery, but if your doctor has recommended that you have this operation, it will be because the risk of losing your vision completely from uncontrolled glaucoma is far worse than this possible side effect of the surgery.

Some patients need a small change in their glasses prescription but this should be done not earlier than at least 3 months after surgery and only once the IOP has stabilised. It is advisable to check with your ophthalmologist before changing glasses or if you find that you need to acquire glasses for the first time following the surgery. Contact lens wear, however, can typically be restarted about 4 weeks or sometimes sooner following aqueous shunt implantation.

Post-operative eye infection can occur, but serious infection is uncommon.

On very rare occasions (<1% of cases), further surgical intervention (such as viscoelastic gel or gas injection into the eye in the clinic, or a further operation to reduce the drainage through the tube) may be recommended if the eye pressure drops very low or very quickly very soon after surgery. This is because very low eye pressure very soon after surgery may cause bleeding (a choroidal haemorrhage) at the back of the eye. For this reason, it is very important to attend your follow-up clinic appointments strictly as directed.

Excessively low IOP is usually detected during your follow-up clinic assessments, but although often painless, very low IOP may be associated with a throbbing or dull aching sensation in the operated eye. Should you experience these symptoms, or any excessive pain, increasing eye redness, sticky eye with a persistent sticky discharge, sudden severe visual change such as darkening, veil or spider web shadow, or flashing lights, you should not hesitate to seek medical advice urgently, for example, at the eye casualty department.

In some cases of aqueous shunt implantation, it is usual to expect that a second small operation (referred to as “occluding suture or ligature removal”) may be required about 2-3 months later, to improve the flow of fluid out of the eye & to start lowering the high IOP. In such a case, you may need to use glaucoma drops between the 1st and 2nd operations.