Glaucoma Surgery — How It Works, Benefits & Recovery — Procedure Guide, Recovery & Risks | MyMedicPlus

Glaucoma surgery encompasses a range of surgical and laser procedures designed to lower intraocular pressure (IOP) in patients with glaucoma — a progressive optic neuropathy in which elevated IOP damages retinal ganglion cell axons in the optic nerve, leading to irreversible peripheral and eventually central visual field loss. The therapeutic goal is to reduce IOP to the patient's individual 'target pressure' — typically 12–15 mmHg or lower in advanced disease — at which further optic nerve damage is halted or substantially slowed. Surgery does not reverse existing visual field loss. Glaucoma surgical procedures fall into three broad categories. Filtering surgery (trabeculectomy) creates a new drainage channel through the sclera into a subconjunctival reservoir (bleb), bypassing the blocked trabecular meshwork and allowing aqueous humour to drain out of the eye. Tube shunt surgery (Ahmed or Baerveldt implants) channels aqueous humour through a silicone tube in the anterior chamber to an equatorial plate under the conjunctiva where it is absorbed. Minimally invasive glaucoma surgery (MIGS) includes a family of micro-implants and laser procedures (iStent inject, Hydrus, Kahook Dual Blade, gonioscopy-assisted transluminal trabeculotomy, cyclophotocoagulation) that lower IOP through novel drainage pathways with lower surgical risk, shorter recovery, and less IOP reduction than conventional filtering surgery. Selective laser trabeculoplasty (SLT) is a laser treatment often considered before incisional surgery.

Glaucoma surgery is indicated when IOP cannot be controlled at target levels using maximum tolerated medical therapy (topical prostaglandin analogues, beta-blockers, carbonic anhydrase inhibitors, alpha-agonists) and laser trabeculoplasty, or when disease progression continues despite pharmacological treatment. Specific surgical indications include: failure of two or more classes of topical medications to achieve target IOP, intolerable side effects from glaucoma drops (surface ocular disease, systemic effects in elderly patients), poor adherence to multiple-drop regimens that cannot be reliably maintained, progressive glaucomatous visual field loss or optic nerve structural damage despite apparently adequate medical IOP control, advanced glaucoma requiring IOP in the low-to-mid teens that drops cannot achieve, and newly diagnosed patients with very high presenting IOP (above 35 mmHg) or very advanced disc cupping who require immediate IOP reduction. MIGS procedures are generally combined with cataract surgery in patients with mild-to-moderate glaucoma. Trabeculectomy or tube shunts are preferred for more advanced disease or when larger IOP reductions are needed. The choice between trabeculectomy and tube shunt is guided by prior surgical history, conjunctival status, glaucoma severity, and surgeon experience; the TVT study showed comparable outcomes at 5 years.

Trabeculectomy: performed under local anaesthetic peribulbar or sub-Tenon block with sedation as a day case. The eye is prepared and draped. A limbal or fornix-based conjunctival peritomy exposes the superior sclera. An adjuvant antimetabolite — mitomycin-C (MMC) sponges 0.2–0.4 mg/ml, or 5-fluorouracil 50 mg/ml — is applied subconjunctivally for 1–3 minutes to inhibit fibroblast proliferation and prevent bleb scarring; the area is thoroughly irrigated. A partial-thickness rectangular scleral flap (approximately 3×4 mm) is fashioned and a sclerostomy (trabeculo-corneectomy) performed under the flap using a punch or blade to create the new drainage channel. A peripheral iridectomy prevents iris from blocking the sclerostomy. The scleral flap is sutured loosely with releasable sutures to regulate initial flow. The conjunctiva is closed with absorbable sutures. Tube shunts: the tube end of a silicone tube attached to a polypropylene equatorial plate is inserted through a 23-gauge needle pars plana or limbal sclerotomy into the anterior or posterior chamber. The plate is sutured to the episclera. Patch graft (donor pericardium or cornea) covers the tube at the limbus to prevent erosion. MIGS: most MIGS devices are inserted via a 1–2 mm temporal clear corneal incision under gonioscopic visualisation in the same session as phacoemulsification cataract surgery.

The overriding benefit of glaucoma surgery is sustained, medication-independent IOP reduction that preserves remaining vision by halting or slowing further optic nerve damage. Trabeculectomy achieves IOP below 15 mmHg without drops in 70–80% of patients at 1 year and approximately 50–60% at 5 years — a degree of IOP lowering unattainable with maximum medical therapy in most advanced glaucoma patients. This marked IOP reduction dramatically slows the rate of visual field loss, preserving quality of life and independence. The elimination of multiple eye drop medications confers secondary benefits: many glaucoma patients have severe ocular surface disease from years of preserved eye drops; trabeculectomy allows drops to be stopped, resolving surface inflammation and improving comfort and visual acuity. The Medical Treatment of Glaucoma Study showed that trabeculectomy reduced the rate of visual field progression from 2.5 dB/year to 0.4 dB/year over 5 years. Tube shunts (Ahmed, Baerveldt) provide IOP reduction in previously operated eyes where conjunctival scarring makes trabeculectomy less likely to succeed. MIGS procedures offer IOP reduction of 2–6 mmHg with a very favourable safety profile and rapid recovery, particularly suitable for mild-to-moderate glaucoma combined with cataract extraction.

Hypotony (IOP too low, below 6 mmHg) in the early post-operative period causes choroidal effusions, macular folds, and transient visual blurring; managed by adjusting releasable sutures and antimetabolite treatment. Bleb failure from fibrosis is the principal cause of long-term failure of trabeculectomy, occurring in 20–30% at 5 years; managed with bleb needling with 5-FU injection or repeat surgery. Bleb-related infection (blebitis, endophthalmitis) is the most serious late complication, affecting 1–2% of trabeculectomy patients over a lifetime and can cause catastrophic visual loss — thin, avascular blebs created with heavy MMC use are particularly at risk. Cataract formation or progression is accelerated after filtering surgery, occurring in approximately 30% at 5 years. Tube shunt complications include tube erosion (requiring patch graft revision), diplopia from plate-induced strabismus, corneal decompensation from tube contact, and, rarely, tube occlusion from iris, vitreous, or fibrin. MIGS carries lower rates of serious complications (hypotony, endophthalmitis, tube erosion) at the cost of less pronounced IOP lowering. Importantly, no glaucoma surgical procedure can restore visual field already lost to optic nerve damage.

Post-operative care after trabeculectomy is intensive and requires frequent clinic visits. A steroid-antibiotic eye drop combination (prednisolone and chloramphenicol, or ciprofloxacin) is instilled hourly for the first few days and tapered over 4–6 weeks — steroid titration is critical to bleb modulation. Releasable scleral flap sutures are removed in the outpatient clinic in the first 2–3 weeks using a slit lamp to adjust aqueous drainage based on bleb appearance and IOP. Activities restricting eye rubbing (contact sports, swimming) are avoided for 6 weeks. No heavy lifting or straining for 4 weeks. Vision is reduced and fluctuating for 4–6 weeks as the bleb matures. At 1 month, bleb needling with subconjunctival 5-FU injection may be performed to prevent fibrosis if the IOP is rising. At 3 months, the bleb is considered established. Patients are reviewed 3-monthly in the first year and 6-monthly thereafter. Glaucoma drops are typically stopped after successful surgery; they may be restarted selectively if IOP rises. Lifelong optic nerve monitoring with OCT nerve fibre layer analysis and automated visual field testing every 6–12 months is mandatory to detect any progressive structural or functional change.