Author: Claude (AI), from PubMed abstracts · Reviewed by: Dr Mina Abdelmseih · Reviewed: 2026-11-15 · Review due: 2027-11-15

Educational content only. Not personalised medical advice. Clinical decisions remain the responsibility of the treating clinician.

Glaucoma Drainage Devices

Glaucoma drainage devices (tube shunts) are used for refractory glaucoma and, increasingly, as a primary operation [S1] [S7]. Valved (Ahmed) and non-valved (Baerveldt, Paul, Aurolab) implants trade safety against pressure lowering [S2] [S11] [S12], and a low-cost non-valved implant compared well with the Ahmed valve [S8].

Key points - In eyes with previous trabeculectomy or cataract surgery, a Baerveldt tube had lower 5-year failure than trabeculectomy with MMC (29.8% vs 46.9%) [S1]. - In eyes with no previous incisional surgery, tube and trabeculectomy had similar IOP and failure at 5 years, but tubes needed more medications (2.2 vs 1.3) [S7]. - The Baerveldt implant lowered IOP more and needed fewer reoperations than the Ahmed valve, but failed more often for safety reasons (persistent hypotony, explantation, loss of light perception) [S2]; the Ahmed valve had less persistent hypotony and choroidal effusion [S11]. - The Aurolab aqueous drainage implant (AADI) achieved higher complete success than the Ahmed valve (OR 3.64) with similar adverse events [S8]. - Lower preoperative IOP, neovascular glaucoma, Ahmed implantation and younger age predicted tube failure [S6].

Evidence last checked: 2026-10-17 (PubMed abstracts).

Red flags

• Tube exposure: the most common late complication after Baerveldt surgery in neovascular glaucoma [S5]; Baerveldt implants had more tube erosion than trabeculectomy [S10].
• Hypotony and choroidal effusion: persistent hypotony occurred in 4.4% after Baerveldt vs 0.6% after Ahmed in RCTs [S11].
• Diplopia or strabismus: more frequent after Baerveldt than trabeculectomy [S10].
• Vision loss: occurred in 18.9% after Baerveldt vs 9% after Ahmed in pooled data [S11].

Recognise it: who needs a tube

• Uncontrolled glaucoma after previous trabeculectomy or cataract extraction [S1].
• Refractory glaucoma or previous intraocular surgery [S2] [S8] [S12].
• Medically uncontrolled glaucoma without previous surgery, as an alternative to trabeculectomy [S7].
• Neovascular glaucoma, where tube failure risk is higher (HR 1.79) [S6]; a Japanese RCT found trabeculectomy and Baerveldt implant similarly successful, with fewer late complications after trabeculectomy [S5].

Confirm it: judging outcome

• Trials defined failure as IOP above 21 mmHg or reduced less than 20% from baseline, IOP of 5 mmHg or less, reoperation for glaucoma, or loss of light perception [S1].
• Mean 5-year IOP was 12.7 to 14.7 mmHg across tube trials [S1] [S2] [S7].
• Anterior segment OCT was used to monitor patch graft thinning over the tube [S4].

Manage it

Before acting on this section, check the national and local guidelines, product information and regulatory approvals that apply where you practise. See the medical disclaimer.

Tier A (primary care / no specialist)

• No tube management at this level. Patients with a tube who develop a red, painful eye, an exposed tube or reduced vision need the eye unit the same day.

Tier B (general eye clinic)

• Examine the conjunctiva over the tube for thinning or exposure [S4] [S5], and check for double vision [S10].
• Expect patients to need some drops after a tube: mean 1.4 to 2.2 medications at 5 years [S1] [S2] [S7].

Tier C (specialist centre)

1. Tube or trabeculectomy. A meta-analysis of 49 studies found the Ahmed valve similar to trabeculectomy for IOP with fewer adverse events, and the Baerveldt implant less effective for IOP but with fewer bleb leaks, hyphaema and hypotony maculopathy [S10]. Cochrane found the IOP difference between shunts and trabeculectomy at 1 year uncertain (very low certainty) [S3].
2. Choosing a device. Ahmed had higher IOP at 1 year (MD 2.60 mmHg) and more reoperations than Baerveldt (moderate certainty) [S3]. Ahmed has a safer hypotony profile [S11]. Choose by patient risk [S11].
3. Low-cost devices. The AADI lowered IOP more and needed fewer medications than the Ahmed valve in 6 studies of 825 eyes [S8], relevant where device cost limits access.
4. Newer implants. The Paul implant reduced IOP by 14.8 to 19.1 mmHg with complete success of 38.4% to 75%; evidence is mostly uncontrolled with short follow-up [S12].
5. Covering the tube. Amniotic membrane-umbilical cord grafts thinned less than pericardium (early thinning 12% vs 43%), with similar exposure rates [S4].
6. Neovascular glaucoma. Intravitreal bevacizumab with Ahmed valve and panretinal photocoagulation was studied in RCTs; anti-VEGF improved IOP control at 1 month (RR 1.32, low certainty) [S9].

Refer when

Pitfalls

• Assuming all tubes behave alike: valved and non-valved devices differ in IOP and safety [S2] [S11].
• Missing early conjunctival thinning over the tube [S4].
• Expecting drop-free control after a tube [S7].
• Using the higher-cost device by default where a low-cost implant performs at least as well [S8].

Evidence notes

• TVT and PTVT enrolled different populations (previous surgery vs none), which explains different conclusions [S1] [S7].
• The AADI meta-analysis included non-randomised studies; design details are not given in the abstract [S8].
• Not covered by these sources: surgical technique, tube position choice, management of tube exposure, childhood and uveitic glaucoma tubes, and device cost figures.

Related articles

• Trabeculectomy
• Childhood Glaucoma

References

See the numbered source list below. Each marker [S#] links to its PubMed and DOI record.