A 55-year-old patient on maximum tolerated topical therapy (prostaglandin + beta-blocker + CAI) still has IOP of 22 mmHg with progressive optic nerve damage. She has a history of recurrent bleb-related infections. The surgeon considers a tube-shunt procedure (Baerveldt or Ahmed). What is the advantage of a non-valved (Baerveldt) over a valved (Ahmed) glaucoma drainage device?

• A Non-valved devices have a lower risk of hypotony in the early postoperative period
• B Non-valved devices do not require a restrictive suture or tube ligation technique
• C Valved devices provide better long-term IOP control than non-valved devices
• D Non-valved devices achieve lower long-term IOP due to larger plate surface area with unrestricted flow after the fibrotic capsule matures ✓

Explanation

The Baerveldt implant is a non-valved (unvalved) device with a large plate (250 or 350 mm²) that achieves lower long-term IOP than the valved Ahmed device because once the fibrous capsule around the plate matures (6–8 weeks post-op), aqueous drains freely without a flow-restrictor. The TVT study showed Baerveldt achieves lower IOP at 5 years compared to trabeculectomy. The Ahmed valve restricts outflow to avoid early hypotony, but this same resistance limits long-term IOP reduction. Non-valved devices require a temporary tube occlusion suture or ripcord to prevent early hypotony.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.