Glaucoma Surgery: Types, Suitability, Risks and Recovery

Author: Dr Val Phua
Estimated reading time: 24 minutes

Glaucoma surgery is performed to lower intraocular pressure and reduce the risk of further optic-nerve damage.

It may be considered when:

• Eye drops and laser treatment do not lower pressure sufficiently
• Glaucoma continues to progress despite apparently acceptable pressure
• The required target pressure is unlikely to be achieved with medication alone
• Eye drops cause significant side effects
• The patient cannot use drops reliably
• The treatment burden has become excessive
• The drainage angle or other eye anatomy requires surgical correction
• Glaucoma is advanced and only a small amount of useful vision remains
• Cataract surgery provides an opportunity to perform a combined glaucoma procedure

There is no single operation called “glaucoma surgery”.

Glaucoma procedures include:

• Trabeculectomy
• Glaucoma drainage implants or tube shunts
• Subconjunctival microshunts
• Trabecular bypass stents
• Schlemm’s canal scaffolds
• Goniotomy
• Trabeculotomy
• Canaloplasty
• Deep sclerectomy
• Cyclophotocoagulation
• Procedures combined with cataract surgery

These operations lower pressure in different ways.

Some create a new drainage pathway beneath the conjunctiva.

Others improve the eye’s natural drainage system.

Cyclophotocoagulation reduces the amount of aqueous fluid produced inside the eye.

Glaucoma surgery does not reverse optic-nerve damage or restore vision that has already been permanently lost.

Its purpose is to preserve remaining vision by achieving pressure control appropriate for the individual eye.

Large randomised trials show that both trabeculectomy and tube-shunt surgery can achieve sustained pressure reduction into the low teens. The relative advantages depend heavily on whether the eye has undergone previous surgery, how low the target pressure is and which complications are most important for that patient.

The Quick Answer

What Is the Main Aim of Glaucoma Surgery?

The main aim is to lower intraocular pressure sufficiently to reduce the risk of further glaucomatous damage.

Success may mean:

• Reaching the target pressure
• Slowing or stopping visual-field progression
• Reducing the number of glaucoma drops
• Avoiding another operation
• Preventing a painful pressure rise
• Preserving useful vision

A technically successful procedure does not necessarily mean that the patient will need no further treatment.

Can Glaucoma Surgery Cure Glaucoma?

No.

The patient continues to have glaucoma or a lifelong risk of glaucomatous progression.

Continued monitoring is required with:

• Eye-pressure measurements
• Optic-nerve examination
• OCT imaging
• Visual-field testing
• Assessment of the operation or implant

Can Surgery Restore Lost Vision?

Vision lost because of established optic-nerve damage usually cannot be restored.

Temporary blur related to pressure, cataract, corneal swelling or medication may sometimes improve, but established glaucomatous field loss is generally permanent.

When Is Surgery Recommended?

Surgery may be recommended when the risk of further glaucoma damage is greater than the risk of the operation.

The decision depends on:

• Severity of glaucoma
• Rate of progression
• Current pressure
• Target pressure
• Number and tolerability of medications
• Previous laser treatment
• Previous eye surgery
• Cataract
• Drainage-angle anatomy
• Condition of the conjunctiva
• Age and life expectancy
• Vision in the other eye
• Ability to attend intensive follow-up

Is Glaucoma Surgery Painful?

Most glaucoma operations are performed using:

• Anaesthetic eye drops
• Local anaesthetic injection
• Sedation
• General anaesthesia in selected patients

Patients may feel:

• Pressure
• Movement
• Touch
• Bright light
• Fluid around the eye

Sharp pain is not expected and should be reported immediately.

How Long Does Surgery Take?

The procedure may take approximately:

• 20 to 45 minutes for a straightforward angle-based procedure
• 30 to 60 minutes for trabeculectomy
• 45 to 90 minutes for a drainage implant
• Longer for complex or combined operations

The total hospital or surgical-centre visit is longer because of preparation, anaesthesia and postoperative observation.

How Long Is Recovery?

Recovery varies significantly.

After trabeculectomy or tube-shunt surgery:

• Vision is commonly blurred for several days or weeks.
• Frequent reviews are required.
• Eye drops may be needed for several weeks or months.
• The operation may require adjustment during healing.
• Final pressure stability may take several months.

Recovery after uncomplicated angle-based minimally invasive glaucoma surgery is often faster, particularly when combined with cataract surgery.

Understanding Eye Pressure and Glaucoma

How Is Aqueous Fluid Produced?

Aqueous humour is produced by the ciliary body behind the iris.

It normally flows:

• Through the pupil
• Into the anterior chamber
• Through the trabecular meshwork
• Into Schlemm’s canal
• Into collector channels and veins

Why Does Pressure Rise?

Pressure may rise when:

• The trabecular meshwork does not drain efficiently
• The drainage angle is closed
• Scar tissue obstructs aqueous outflow
• Pigment or inflammatory material blocks drainage
• Abnormal blood vessels cover the drainage angle
• Previous surgery changes eye anatomy
• Aqueous production exceeds effective drainage

What Is the Target Pressure?

The target pressure is the level considered sufficiently low to reduce the risk of further damage.

It is not the same for every patient.

A patient with:

• Early, slowly progressing glaucoma may tolerate a moderate pressure.
• Advanced glaucoma may require a pressure in the low teens.
• Rapidly progressing or very advanced disease may require an even lower target.

The target may change if OCT or visual-field testing shows continued progression.

When Is Surgery Better Than More Eye Drops?

Adding another glaucoma drop may be reasonable when:

• Glaucoma is mild or moderate
• The pressure is close to target
• Medication is tolerated
• Adherence is reliable
• Progression is slow
• Surgical risk is relatively high

Surgery may become preferable when:

• Several medications are already required
• The required target pressure is very low
• The patient cannot tolerate preservatives or drug effects
• Medication adherence is unreliable
• Visual fields continue worsening
• The ocular surface is significantly damaged
• The disease is advanced
• Previous laser treatment has been insufficient
• Cataract surgery is already planned

Surgery should not be considered only after all useful vision has been lost.

Waiting until glaucoma becomes extremely advanced may reduce the visual reserve available to tolerate temporary postoperative pressure fluctuation, inflammation or complications.

The Main Categories of Glaucoma Surgery

Bleb-Forming Surgery

These operations direct aqueous fluid from inside the eye into a reservoir beneath the conjunctiva.

Examples include:

• Trabeculectomy
• XEN gel stent
• PreserFlo MicroShunt
• Some other subconjunctival drainage procedures

The fluid collects in a filtering area called a bleb.

Glaucoma Drainage Implants

These procedures use a tube and an external plate.

Examples include:

• Ahmed glaucoma valve
• Baerveldt glaucoma implant
• Other valved or non-valved tube systems

Angle-Based Surgery

These procedures act on the trabecular meshwork and Schlemm’s canal.

Examples include:

• Trabecular bypass stents
• Schlemm’s canal scaffolds
• Goniotomy
• Trabeculotomy
• Canaloplasty
• Combined trabeculotomy and canaloplasty

Non-Penetrating Surgery

These operations improve drainage without creating a full-thickness opening into the anterior chamber.

Examples include:

• Deep sclerectomy
• Viscocanalostomy
• Ab externo canaloplasty

Cyclodestructive or Cyclomodulatory Treatment

These procedures reduce aqueous production by treating the ciliary body.

Examples include:

• Micropulse transscleral cyclophotocoagulation
• Continuous-wave cyclophotocoagulation
• Slow-coagulation cyclophotocoagulation
• Endoscopic cyclophotocoagulation

Trabeculectomy

What Is a Trabeculectomy?

Trabeculectomy is a filtering operation that creates a controlled pathway for aqueous fluid to leave the eye.

Fluid passes:

• From the anterior chamber
• Beneath a partial-thickness scleral flap
• Into the space under the conjunctiva

This forms a filtering bleb, usually beneath the upper eyelid.

Trabeculectomy remains an important procedure when a low target pressure is required.

Who May Need Trabeculectomy?

Trabeculectomy may be considered for:

• Advanced primary open-angle glaucoma
• Normal-tension glaucoma requiring very low pressure
• Pseudoexfoliative glaucoma
• Pigmentary glaucoma
• Selected angle-closure glaucoma after the angle mechanism has been addressed
• Progressive glaucoma despite medication and laser
• Glaucoma in which a minimally invasive procedure is unlikely to achieve the target
• Eyes without extensive conjunctival scarring
• Selected congenital, juvenile or secondary glaucomas

Why Can Trabeculectomy Achieve Low Pressure?

Trabeculectomy bypasses much of the eye’s natural drainage resistance.

The flow is controlled by:

• The scleral flap
• Flap sutures
• Conjunctival healing
• Postoperative scarring
• Adjustment procedures
• The pressure difference between the eye and the bleb

Because the new pathway is not limited by the normal episcleral venous pressure in the same way as many angle-based procedures, trabeculectomy can often achieve lower pressures.

How Is Trabeculectomy Performed?

Step 1: Anaesthesia and Preparation

The eye is numbed and cleaned.

An eyelid holder is placed.

Step 2: Opening the Conjunctiva

The surgeon opens the conjunctiva to expose the sclera.

The opening may be:

• Fornix-based
• Limbus-based

Step 3: Applying an Antimetabolite

Mitomycin C or 5-fluorouracil may be applied to reduce postoperative scarring.

These medications reduce fibroblast activity and improve the chance that the drainage pathway remains open.

Mitomycin C is widely used when a stronger antifibrotic effect is desired. Randomised studies have shown that both mitomycin C and 5-fluorouracil can improve filtration outcomes, although dosing and complication profiles vary.

Step 4: Creating the Scleral Flap

A partial-thickness flap is created in the white wall of the eye.

This flap acts as a resistance valve over the new drainage opening.

Step 5: Entering the Anterior Chamber

A small block of deeper scleral and trabecular tissue is removed.

This creates a pathway from the anterior chamber.

Step 6: Performing an Iridectomy

A small piece of peripheral iris is commonly removed to prevent iris tissue from blocking the internal opening.

Step 7: Suturing the Scleral Flap

The flap is sutured.

The number and tension of the sutures help regulate fluid flow.

Step 8: Closing the Conjunctiva

The conjunctiva is closed watertight.

A filtering bleb begins to form beneath it.

What Is the Filtering Bleb?

The bleb is an elevated or diffuse area beneath the conjunctiva where aqueous fluid collects before being absorbed.

A healthy bleb may appear:

• Diffuse
• Mildly elevated
• Relatively pale
• Posteriorly spread
• Quiet and comfortable

A bleb that is excessively scarred may become flat and stop draining.

An excessively thin or avascular bleb may be more prone to leakage and late infection.

Why Is Mitomycin C Used?

The body naturally attempts to heal and close the surgically created pathway.

Mitomycin C reduces scarring and may improve the chance of achieving a low pressure.

However, stronger antifibrotic treatment can also increase the risk of:

• Thin blebs
• Leakage
• Hypotony
• Late bleb infection

The concentration, area and duration of application are individualised according to the patient’s scarring risk.

Postoperative Adjustment After Trabeculectomy

Trabeculectomy is not always complete when the patient leaves the operating theatre.

The result is often actively managed during the first several weeks.

Possible interventions include:

• Digital ocular massage
• Laser suture lysis
• Removal of releasable sutures
• Needling of scar tissue
• Subconjunctival 5-fluorouracil
• Subconjunctival mitomycin C
• Reforming a shallow anterior chamber
• Repairing a leaking bleb
• Revising the filtration site

These interventions are part of postoperative management rather than necessarily indicating that the original surgery was performed incorrectly.

Laser Suture Lysis

Laser suture lysis cuts selected scleral-flap sutures through the conjunctiva.

It may be performed when:

• The pressure is above target
• The bleb is under-functioning
• The anterior chamber is sufficiently deep
• Excessive flow is not expected

Bleb Needling

Needling uses a fine needle to break scar tissue around the bleb.

An antimetabolite may be injected to reduce recurrent scarring.

Needling may restore drainage without a full repeat operation.

How Effective Is Trabeculectomy?

Trabeculectomy can achieve substantial and durable pressure reduction.

In the Primary Tube Versus Trabeculectomy trial, previously unoperated eyes undergoing trabeculectomy achieved a mean pressure of approximately 13 mmHg at five years and required fewer medications than eyes receiving a primary Baerveldt tube. The cumulative failure rate was not significantly different between the procedures.

Trabeculectomy produced lower pressure and fewer medications during the first year of that study, but early complications were more frequent than with tube surgery.

Risks of Trabeculectomy

Possible early complications include:

• Low eye pressure
• Shallow anterior chamber
• Choroidal effusion
• Choroidal haemorrhage
• Hyphema
• Corneal swelling
• Bleb leak
• Inflammation
• Infection
• Raised pressure from excessive scarring
• Cataract progression
• Temporary reduction in vision

Possible late complications include:

• Bleb failure
• Persistent hypotony
• Hypotony maculopathy
• Thin or leaking bleb
• Late bleb infection
• Endophthalmitis
• Cataract
• Irregular astigmatism
• Dysesthesia from the bleb
• Need for repeat glaucoma surgery

Low Eye Pressure After Trabeculectomy

Low pressure is called hypotony.

A low numerical pressure does not always cause harm.

It becomes clinically important when associated with:

• Blurred vision
• Choroidal effusion
• Corneal folds
• Shallow anterior chamber
• Optic-disc swelling
• Hypotony maculopathy

Treatment may include:

• Reducing steroid medication
• Stopping pressure-lowering drops
• Cycloplegic drops
• Injection of viscoelastic
• Placement of an additional scleral-flap suture
• Bleb revision

Bleb Infection

A filtering bleb creates a lifelong route of relative weakness in the ocular surface.

Warning symptoms include:

• Red eye
• Pain
• Discharge
• Light sensitivity
• Rapidly worsening vision
• A white or cloudy bleb

Bleb-related infection requires urgent treatment because it can progress to endophthalmitis.

Glaucoma Drainage Implants

What Is a Glaucoma Drainage Implant?

A glaucoma drainage implant consists of:

• A small silicone tube
• A plate positioned on the outside of the eye beneath the conjunctiva

The tube carries aqueous fluid from the anterior chamber to the plate.

A fibrous capsule forms around the plate, and fluid is absorbed through this capsule.

When Is a Tube Shunt Used?

Tube surgery may be considered for:

• Glaucoma after failed trabeculectomy
• Significant conjunctival scarring
• Previous retinal surgery
• Neovascular glaucoma
• Uveitic glaucoma
• Aphakic glaucoma
• Glaucoma after corneal transplantation
• Eyes with previous cataract surgery
• Congenital or developmental glaucoma
• Primary surgery in selected uncontrolled eyes
• Eyes judged to have a high risk of trabeculectomy failure

Valved and Non-Valved Implants

Valved Implant

A valved implant, such as an Ahmed valve, allows aqueous flow immediately but is designed to resist excessive early flow.

Potential advantages include:

• Earlier pressure reduction
• Lower early hypotony risk
• No need to wait for a ligature to dissolve

Non-Valved Implant

A non-valved implant, such as a Baerveldt device, has no internal flow-limiting valve.

The tube is commonly tied off temporarily while a capsule forms around the plate.

Potential advantages include:

• A larger drainage plate
• Lower long-term pressure in some studies
• Fewer medications in selected populations

Potential disadvantages include:

• Delayed full function
• A period of pressure elevation before the tube opens
• Risk of hypotony when flow begins

Randomised Ahmed-versus-Baerveldt trials found that Baerveldt implants generally achieved lower pressures with fewer medications, but they also carried a greater risk of hypotony-related failure.

How Is Tube-Shunt Surgery Performed?

Step 1: Positioning the Plate

The plate is sutured to the sclera beneath the conjunctiva, usually between two eye muscles.

Step 2: Preparing the Tube

The tube is measured and cut to an appropriate length.

A non-valved tube may be tied closed temporarily.

Step 3: Entering the Eye

A needle tract is created into:

• The anterior chamber
• The ciliary sulcus
• The vitreous cavity in selected eyes

Step 4: Inserting the Tube

The tube is inserted through the tract.

Its position should avoid contact with:

• The cornea
• The iris
• The natural lens
• The intraocular lens

Step 5: Covering the Tube

The external tube is commonly covered using:

• Donor sclera
• Corneal tissue
• Pericardium
• Another patch material

This reduces the risk of conjunctival erosion.

Step 6: Closing the Conjunctiva

The conjunctiva is closed over the plate and tube.

Where Can the Tube Be Positioned?

Anterior Chamber

The tube lies in front of the iris.

This is a common position but may increase concern about long-term corneal endothelial loss if the tube lies too close to the cornea.

Ciliary Sulcus

The tube lies behind the iris and in front of an intraocular lens.

This position may be considered in pseudophakic eyes.

Pars Plana

The tube enters the vitreous cavity.

This requires a vitrectomy and may be considered when:

• The cornea is at particular risk
• An anterior-chamber position is unsuitable
• The eye has complex anterior-segment anatomy

Tube-Shunt Outcomes

In eyes with previous cataract or glaucoma surgery, the Tube Versus Trabeculectomy Study found that tube surgery had a lower five-year failure rate and fewer glaucoma reoperations than trabeculectomy, although the achieved pressures and medication requirements were similar at five years.

In previously unoperated eyes, the Primary Tube Versus Trabeculectomy Study found no statistically significant five-year difference in cumulative failure. Trabeculectomy required fewer medications, whereas tube surgery produced fewer early postoperative complications.

These findings illustrate why the patient’s previous surgery and conjunctival condition materially influence procedure selection.

Risks of Tube-Shunt Surgery

Possible complications include:

• Temporary high pressure
• Low pressure
• Shallow anterior chamber
• Choroidal effusion
• Hyphema
• Inflammation
• Tube blockage
• Tube malposition
• Tube-cornea contact
• Corneal endothelial cell loss
• Double vision
• Eyelid changes
• Tube or plate exposure
• Infection
• Cataract progression
• Retinal complications
• Need for revision or another operation

The Hypertensive Phase

Some eyes develop a temporary rise in pressure several weeks after valved implant surgery.

This is often related to increasing resistance as the capsule around the plate matures.

Treatment may include:

• Restarting glaucoma drops
• Adjusting medication
• Needling the capsule
• Observation
• Further surgery in resistant cases

Tube Exposure

The conjunctiva over the tube or plate may become thin and break down.

An exposed tube increases infection risk and generally requires surgical repair.

Double Vision After a Tube Implant

The plate may affect eye-muscle movement or produce a restrictive capsule.

Double vision may improve with time but can persist.

Management may include:

• Observation
• Prism spectacles
• Strabismus surgery
• Implant revision
• Implant removal in severe cases

A randomised study comparing primary Baerveldt implantation with trabeculectomy found more diplopia after the drainage implant.

Subconjunctival Microshunts

Subconjunctival microshunts create a controlled pathway from the anterior chamber to a filtering bleb.

Examples include:

• XEN gel stent
• PreserFlo MicroShunt

Although often discussed alongside MIGS, these are bleb-forming procedures and can develop many of the same wound-healing issues as trabeculectomy.

XEN Gel Stent

What Is the XEN Gel Stent?

The XEN is a soft gelatin tube implanted from inside the eye or through another surgical approach.

It drains aqueous fluid into the subconjunctival space.

Potential advantages include:

• A small implant
• A relatively standardised internal lumen
• Limited conjunctival dissection during an ab interno procedure
• Faster early visual recovery than traditional trabeculectomy in some patients

Possible limitations include:

• Bleb scarring
• Needling
• Implant obstruction
• Implant exposure
• Failure to reach a very low target pressure

A randomised comparison found that XEN and trabeculectomy achieved broadly similar composite success at one year, although trabeculectomy achieved a somewhat lower average pressure and XEN required a different pattern of postoperative intervention.

PreserFlo MicroShunt

What Is PreserFlo?

PreserFlo is a flexible subconjunctival drainage tube implanted through an external approach.

It creates a controlled route between the anterior chamber and a bleb beneath the conjunctiva and Tenon’s capsule.

Mitomycin C is generally used to reduce scarring.

How Does It Compare with Trabeculectomy?

In a large randomised trial, trabeculectomy had a higher surgical-success rate and achieved lower pressure at two years than the MicroShunt. MicroShunt surgery had fewer certain postoperative complications and interventions but was not equivalent when very low pressure was the main priority.

Published Asian data also show that PreserFlo can meaningfully lower pressure and medication burden, but needling, revision or conversion to trabeculectomy may still be required.

Minimally Invasive Glaucoma Surgery

What Does MIGS Mean?

Minimally invasive glaucoma surgery is a broad term used for procedures that generally aim to:

• Use small incisions
• Minimise tissue disruption
• Provide relatively rapid recovery
• Have a lower rate of severe complications than traditional filtration surgery
• Reduce pressure or medication burden

The term includes procedures with different mechanisms and levels of invasiveness.

Not every MIGS operation provides the same degree of pressure lowering.

Who May Be Suitable for MIGS?

MIGS may be considered for:

• Mild-to-moderate open-angle glaucoma
• Ocular hypertension
• Patients undergoing cataract surgery
• Patients wishing to reduce glaucoma-drop burden
• Patients whose target pressure is not extremely low
• Selected patients who have not tolerated drops or laser
• Selected patients requiring a standalone angle procedure

When May MIGS Be Insufficient?

MIGS may be inappropriate as the sole treatment when:

• Glaucoma is very advanced
• The target pressure is in the very low teens or below
• The drainage angle is extensively closed
• Collector-channel function is poor
• Significant scarring is present
• Rapid progression requires a more powerful operation
• Previous angle surgery has failed
• The glaucoma mechanism is not addressed by the selected procedure

Trabecular Bypass Stents

Trabecular bypass stents create a small route through the trabecular meshwork into Schlemm’s canal.

Examples include iStent devices.

They may be implanted:

• At the time of cataract surgery
• As a standalone procedure in selected settings

A randomised trial found that adding iStent inject to cataract surgery reduced medication burden more than cataract surgery alone over two years in mild-to-moderate glaucoma.

Schlemm’s Canal Scaffolds

A Schlemm’s canal scaffold bypasses the trabecular meshwork and holds open a segment of the canal.

The Hydrus Microstent is an example.

The HORIZON randomised trial found that adding Hydrus to cataract surgery increased the proportion of medication-free eyes and reduced the later need for incisional glaucoma surgery compared with cataract surgery alone over five years.

A secondary analysis also found a slower average rate of visual-field progression in the combined Hydrus group than in the cataract-surgery-only group.

Goniotomy

Goniotomy removes or incises part of the trabecular meshwork from inside the eye.

Possible methods include:

• Excisional goniotomy
• Blade goniotomy
• Electrosurgical trabecular ablation
• Other device-assisted techniques

The procedure exposes Schlemm’s canal and collector channels.

Possible complications include:

• Hyphema
• Temporary pressure elevation
• Peripheral anterior synechiae
• Incomplete pressure lowering
• Need for additional treatment

Trabeculotomy

Trabeculotomy opens the trabecular meshwork and inner wall of Schlemm’s canal.

It may be performed:

• Externally
• From inside the eye
• Over a limited segment
• Over 360 degrees

Circumferential trabeculotomy may use a catheter or suture to treat much of the canal.

Canaloplasty

Canaloplasty uses a microcatheter to pass through Schlemm’s canal.

The canal may be:

• Dilated with viscoelastic
• Tensioned with a suture during ab externo canaloplasty
• Combined with trabeculotomy in an ab interno procedure

Canal-based procedures preserve conjunctiva and do not create a traditional bleb.

Their pressure-lowering effect remains dependent on the distal drainage system.

MIGS Risks

Although MIGS is generally less invasive than trabeculectomy or tube surgery, complications remain possible.

These include:

• Hyphema
• Temporary eye-pressure elevation
• Implant malposition
• Implant obstruction
• Peripheral anterior synechiae
• Corneal injury
• Inflammation
• Cystoid macular oedema
• Failure to lower pressure
• Need for additional medication
• Need for filtration surgery later

“MIGS” should not be interpreted as “no risk”.

Non-Penetrating Glaucoma Surgery

What Is Deep Sclerectomy?

Deep sclerectomy removes deep scleral tissue over Schlemm’s canal while leaving a thin trabeculo-Descemet membrane intact.

Aqueous fluid filters through this membrane without a full-thickness opening into the anterior chamber.

Potential advantages include:

• Lower risk of early severe hypotony
• Less inflammation
• Fewer shallow anterior chambers
• Reduced cataract acceleration in some patients

Potential disadvantages include:

• Technically demanding surgery
• Less predictable very-low-pressure results
• Need for postoperative Nd goniopuncture
• Scarring and failure

Comparative studies suggest that deep sclerectomy can lower pressure effectively with fewer early complications, while trabeculectomy may provide a greater likelihood of complete medication-free control or lower pressure.

Goniopuncture After Deep Sclerectomy

Nd laser may be used to create a small opening through the residual trabeculo-Descemet membrane.

This converts the procedure into a more direct drainage pathway when the pressure remains above target.

Glaucoma Surgery Combined with Cataract Surgery

Cataract and glaucoma commonly occur together.

Possible strategies include:

• Cataract surgery alone
• Cataract surgery with a trabecular stent
• Cataract surgery with goniotomy
• Cataract surgery with canaloplasty or trabeculotomy
• Cataract surgery with endoscopic cyclophotocoagulation
• Combined cataract surgery and trabeculectomy
• Cataract surgery combined with a tube shunt
• Staged cataract and glaucoma operations

Does Cataract Surgery Lower Eye Pressure?

Cataract surgery can lower pressure in some eyes, particularly when:

• The angle is narrow
• The natural lens is crowding the anterior chamber
• The preoperative pressure is elevated

However, cataract surgery alone may not achieve the low target required for advanced glaucoma.

Combined Cataract Surgery and MIGS

Combining cataract surgery with an angle-based procedure may:

• Reduce medication burden
• Provide additional pressure lowering
• Avoid a separate operation
• Preserve the conjunctiva

Randomised trials of Hydrus and iStent support greater medication reduction or pressure control when the device is added to cataract surgery compared with cataract surgery alone.

Combined Cataract Surgery and Trabeculectomy

A combined operation may be considered when:

• A visually significant cataract is present
• Glaucoma requires substantial pressure reduction
• Two separate operations are undesirable

Potential limitations include:

• More inflammation
• Greater scarring stimulus
• Less predictable filtration than a standalone trabeculectomy in some eyes
• More complex postoperative management

Staging the operations may sometimes provide better control, particularly when a very low target pressure is required.

Cyclophotocoagulation

Cyclophotocoagulation reduces aqueous-fluid production by treating the ciliary body.

Options include:

• Micropulse transscleral treatment
• Continuous-wave treatment
• Slow-coagulation treatment
• Endoscopic cyclophotocoagulation

Cyclophotocoagulation may be considered when:

• Previous surgery has failed
• The eye is anatomically complex
• Conjunctival surgery is undesirable
• Glaucoma is refractory
• The eye is painful
• The patient is unsuitable for a longer incisional procedure

Modern micropulse techniques may be used in selected seeing eyes, but repeat treatment or additional medication is often required.

Selecting the Correct Operation

No operation is universally best.

The choice depends on:

• Glaucoma type
• Disease severity
• Target pressure
• Starting pressure
• Previous eye surgery
• Conjunctival scarring
• Cataract status
• Corneal health
• Drainage-angle anatomy
• Retinal surgery history
• Ability to attend follow-up
• Patient preference
• Surgeon experience

Mild Glaucoma

Possible approaches include:

• Cataract surgery with MIGS
• Standalone angle surgery
• Continued drops
• Repeat laser treatment
• Observation when pressure is already controlled

Moderate Glaucoma

Possible approaches include:

• MIGS
• Subconjunctival microshunt
• Trabeculectomy
• Tube implant
• Combined cataract and glaucoma surgery

The target pressure and rate of progression are especially important.

Advanced Glaucoma

Advanced glaucoma often requires:

• Trabeculectomy
• Tube-shunt surgery
• A powerful subconjunctival procedure
• Cyclophotocoagulation in selected eyes

An angle-based MIGS procedure may be insufficient if the target pressure must be extremely low.

Normal-Tension Glaucoma

Patients may have progressive glaucomatous damage despite pressures within the statistically normal range.

Surgery may be considered when:

• Progression is confirmed
• A very low target pressure is required
• Medication and laser are insufficient

The narrower margin between the target pressure and hypotony means that surgical planning and follow-up require particular care.

Angle-Closure Glaucoma

Management may include:

• Laser peripheral iridotomy
• Cataract or clear-lens extraction
• Goniosynechialysis
• Trabeculectomy
• Tube-shunt surgery
• Selected angle-based surgery when the trabecular meshwork is accessible
• Cyclophotocoagulation

The operation should address both:

• The anatomical angle-closure mechanism
• The required target pressure

Pseudoexfoliative Glaucoma

Pseudoexfoliative glaucoma may be associated with:

• Higher pressure
• Greater pressure fluctuation
• More rapid progression
• Weak lens zonules
• Poor pupil dilation

Trabeculectomy, tube surgery, angle procedures and combined cataract surgery may all be considered according to severity.

Pigmentary Glaucoma

Pigmentary glaucoma may respond to:

• Selective laser trabeculoplasty
• Angle surgery
• Trabeculectomy
• Tube surgery

Heavy angle pigmentation can increase the risk of a pressure spike after laser or angle manipulation.

Uveitic Glaucoma

Uveitic glaucoma requires control of inflammation as well as pressure.

Surgery may fail because of:

• Aggressive scarring
• Recurrent inflammation
• Fibrin
• Tube blockage
• Peripheral anterior synechiae

Tube-shunt surgery is commonly considered, but the best operation depends on inflammatory control and anatomy.

Neovascular Glaucoma

Neovascular glaucoma is associated with abnormal blood vessels on the iris and drainage angle.

Treatment may include:

• Retinal laser
• Intravitreal anti-VEGF treatment
• Tube-shunt surgery
• Cyclophotocoagulation
• Pain-control procedures

Trabeculectomy carries a high failure and bleeding risk when neovascular activity is uncontrolled.

Glaucoma After Retinal Surgery

Eyes with previous vitrectomy, scleral buckle or silicone oil may have:

• Scarred conjunctiva
• Altered anatomy
• Secondary angle damage
• Increased inflammation

Tube-shunt surgery or cyclophotocoagulation may be preferred in many of these eyes.

Glaucoma After Corneal Transplantation

The surgical plan should protect the graft endothelium.

Considerations include:

• Tube location
• Risk of tube-cornea contact
• Steroid response
• Conjunctival scarring
• Rejection history
• Need for future graft surgery

Childhood and Developmental Glaucoma

Children may undergo:

• Goniotomy
• Trabeculotomy
• Circumferential trabeculotomy
• Trabeculectomy
• Tube-shunt surgery
• Cyclophotocoagulation

The choice depends on:

• Glaucoma type
• Corneal clarity
• Age
• Previous surgery
• Eye anatomy

Children require long-term monitoring because the eye and refractive prescription continue developing.

The Preoperative Assessment

Medical and Eye History

Important information includes:

• Glaucoma type
• Previous laser procedures
• Previous glaucoma surgery
• Cataract surgery
• Retinal surgery
• Corneal transplantation
• Uveitis
• Eye trauma
• Medication allergies
• Asthma
• Heart disease
• Blood-thinning medication
• Autoimmune disease
• Diabetes
• Ability to use postoperative drops
• Availability of help at home

Visual-Acuity Testing

Vision is measured before surgery.

This provides a baseline and identifies other factors limiting visual potential.

Eye-Pressure Measurement

Pressure may be checked:

• At different times of day
• On and off selected medication
• In both eyes
• Using different instruments

Gonioscopy

Gonioscopy assesses:

• Whether the angle is open or closed
• Trabecular pigmentation
• Peripheral anterior synechiae
• Abnormal blood vessels
• Previous angle surgery
• Suitability for MIGS

Optic-Nerve Examination

The optic nerve is assessed for:

• Rim thinning
• Cupping
• Disc haemorrhage
• Pallor
• Asymmetry

OCT Imaging

OCT may assess:

• Retinal nerve-fibre layer
• Ganglion-cell layer
• Optic-nerve structure
• Progression

Visual-Field Testing

Visual fields help determine:

• Severity
• Rate of progression
• Remaining central vision
• Urgency of pressure reduction
• Appropriate target pressure

Corneal Examination

The surgeon assesses:

• Corneal clarity
• Endothelial health
• Previous scars
• Corneal thickness
• Risk from a tube in the anterior chamber

Conjunctival Examination

The conjunctiva is assessed for:

• Previous incisions
• Scarring
• Inflammation
• Mobility
• Areas suitable for a bleb or plate

Cataract Assessment

The natural lens is examined to determine whether:

• Cataract contributes to visual loss
• Cataract surgery should be combined
• Cataract surgery should occur before or after glaucoma surgery

Retina and Macula

The retina should be assessed when:

• Visual loss is not fully explained by glaucoma
• Diabetes is present
• High myopia is present
• Previous retinal disease exists
• A drainage tube may be placed through the pars plana

Preparing for Surgery

Instructions vary.

Patients may be advised to:

• Continue or stop selected glaucoma drops
• Begin antibiotic or anti-inflammatory drops
• Stop contact-lens wear
• Arrange transport
• Fast if sedation or general anaesthesia is planned
• Discuss anticoagulants with the prescribing doctor
• Arrange help with children, work or household duties

Blood-thinning medication should not be stopped without advice from the prescribing physician and surgeon.

The Day of Surgery

The patient should bring:

• Identification
• Medication list
• Eye drops
• Medical information
• A responsible adult when sedation is used

Before surgery, the team confirms:

• Correct patient
• Correct eye
• Procedure
• Implant model when applicable
• Allergies
• Anaesthetic plan
• Consent

Immediately After Surgery

The eye may be covered with:

• A shield
• A patch
• Both

Temporary symptoms may include:

• Blurred vision
• Grittiness
• Watering
• Mild aching
• Light sensitivity
• Eyelid swelling
• Redness
• Double vision

Severe pain or rapid visual deterioration is not expected and requires urgent assessment.

Eye Drops After Surgery

Medication may include:

• Steroid drops
• Antibiotic drops
• Cycloplegic drops
• Lubricants
• Selected glaucoma drops

Steroid treatment may continue for several weeks or months after bleb surgery.

The regimen is adjusted according to:

• Inflammation
• Bleb appearance
• Pressure
• Scarring response
• Corneal health

Should Existing Glaucoma Drops Continue?

This depends on the operation.

After trabeculectomy, pressure-lowering drops are often stopped in the operated eye initially.

After a non-valved tube implant, drops may be required while the tube remains tied.

After MIGS, drops may continue until the effect is confirmed.

Medication should be changed only according to the surgeon’s instructions.

The First Postoperative Day

The surgeon may assess:

• Vision
• Eye pressure
• Anterior-chamber depth
• Corneal clarity
• Wound integrity
• Bleb function
• Tube position
• Implant position
• Inflammation
• Choroidal effusion

The First Several Weeks

Reviews may be frequent after trabeculectomy.

The surgeon may need to:

• Adjust medication
• Perform suture lysis
• Remove releasable sutures
• Massage the eye
• Inject an antimetabolite
• Needle a bleb
• Treat pressure elevation
• Treat hypotony
• Manage inflammation

How Long Before the Result Is Stable?

Pressure may continue changing for:

• Several weeks after MIGS
• Two to three months after trabeculectomy
• Several months after tube surgery
• Longer when needling or revision is required

The early pressure is not always the final pressure.

Activity After Glaucoma Surgery

Patients are commonly advised to avoid:

• Eye rubbing
• Heavy lifting
• Strenuous exercise
• Contact sports
• Bending with the head far below the waist
• Dusty or dirty environments
• Swimming
• Eye makeup
• Water entering the eye
• Pressure on the operated side

The duration depends on the operation and healing.

Can I Use Screens?

Screens do not damage the operation.

However, prolonged screen use may worsen:

• Dryness
• Eye fatigue
• Fluctuating vision
• Discomfort

When Can I Drive?

Driving should resume only when:

• Vision meets the legal standard
• The surgeon has not advised otherwise
• Depth perception is adequate
• Sedation has fully worn off
• Double vision and glare are manageable

When Can I Return to Work?

This depends on:

• Type of surgery
• Vision
• Pressure stability
• Need for frequent clinic visits
• Physical demands of work
• Exposure to dust or trauma

Office work may resume sooner than:

• Heavy manual work
• Construction
• Military duties
• Contact sports
• Driving occupations

Can I Fly?

Most glaucoma operations do not place a gas bubble inside the eye.

Flying is often possible once the early postoperative condition is stable.

Travel should not interfere with:

• Pressure checks
• Bleb adjustments
• Suture lysis
• Access to urgent care

Expected Visual Recovery

Vision may initially worsen because of:

• Corneal swelling
• Inflammation
• Astigmatic change
• A dilated pupil
• Low pressure
• High pressure
• Hyphema
• Cataract
• Ocular-surface disturbance

Vision may take weeks to stabilise after filtration or tube surgery.

Some patients require an updated spectacle prescription after healing.

Cataract After Glaucoma Surgery

Trabeculectomy and tube surgery may accelerate cataract progression in a phakic eye.

Cataract surgery can usually be performed later, but it may alter the function of a pre-existing bleb.

The cataract surgeon should minimise:

• Conjunctival trauma
• Inflammation
• Bleb manipulation

How Is Surgical Success Defined?

Different studies use different definitions.

Success may require:

• Pressure below a stated level
• A percentage pressure reduction
• Pressure above a hypotony threshold
• No additional glaucoma surgery
• Preservation of light perception
• No medications for complete success
• Medications permitted for qualified success

Success rates from different studies cannot be compared reliably without examining their definitions.

Can Glaucoma Surgery Fail?

Yes.

Failure may result from:

• Scarring
• Implant obstruction
• Tube malposition
• Inadequate distal drainage
• Disease progression despite pressure lowering
• The chosen operation being insufficient for the target
• A pressure that becomes too low
• Complications requiring implant removal or further surgery

What Happens if Surgery Fails?

Options may include:

• Restarting glaucoma drops
• Laser treatment
• Bleb needling
• Bleb revision
• Tube revision
• Implant exchange
• A second tube
• Trabeculectomy
• Cyclophotocoagulation
• Another MIGS procedure in selected cases

General Risks of Glaucoma Surgery

Possible risks include:

• Pain
• Infection
• Bleeding
• Inflammation
• Corneal swelling
• Cataract
• Low pressure
• High pressure
• Choroidal effusion
• Choroidal haemorrhage
• Hypotony maculopathy
• Macular oedema
• Double vision
• Drooping eyelid
• Astigmatism
• Loss of corrected vision
• Need for additional surgery
• Rare severe permanent visual loss

Randomised trabeculectomy-versus-tube trials found that early complications were more frequent after trabeculectomy, while late complication rates became more similar over five years. Most complications were transient, but serious complications occurred after both operations.

Wipe-Out or Snuff-Out

“Wipe-out” describes unexplained severe central visual loss after surgery in an eye with extremely advanced glaucoma.

It appears to be rare with modern surgery.

Potential concerns in advanced glaucoma include:

• Large pressure fluctuation
• Hypotony
• Anaesthetic-related pressure
• Vascular compromise
• Other unrecognised causes of visual loss

The possibility should not be used automatically to deny surgery when uncontrolled pressure is itself threatening the remaining vision.

Common Myths

“Glaucoma Surgery Restores Lost Vision”

False.

Its purpose is to preserve remaining vision.

“Surgery Cures Glaucoma”

False.

Lifelong monitoring remains necessary.

“Surgery Is Only Needed When All Vision Is Nearly Gone”

False.

Earlier surgery may be appropriate when progression cannot be controlled safely.

“Trabeculectomy Is Outdated”

False.

It remains one of the most effective procedures for achieving a low target pressure.

“MIGS Is Always Better Because It Is Safer”

False.

MIGS may provide a more favourable safety and recovery profile but may not lower pressure enough for advanced disease.

“A Tube Implant Works Immediately”

Not always.

Non-valved tubes are commonly tied closed temporarily.

“A Filtering Bleb Is an Infection”

False.

A bleb is an intended drainage reservoir.

However, blebs can become infected.

“Needing Suture Lysis Means the Trabeculectomy Failed”

False.

Suture adjustment is a common part of postoperative management.

“No Drops After Surgery Means No More Follow-Up”

False.

Pressure can rise again and glaucoma can continue progressing.

“A Low Pressure Is Always Better”

False.

Pressure that is too low can damage vision.

“A Normal Pressure Means Glaucoma Is Stable”

False.

OCT and visual fields are required to assess progression.

“Glaucoma Surgery Always Causes Cataract”

False.

Cataract progression is a recognised risk, but not every patient develops a visually significant cataract.

“A Tube Can Fall Out”

The implant cannot fall out during ordinary activity.

The conjunctiva may rarely erode over the tube, requiring surgical repair.

Frequently Asked Questions

Which Glaucoma Operation Is Best?

The best operation is the one most likely to reach the required target pressure with an acceptable risk profile for that eye.

Is Trabeculectomy Better Than a Tube?

It depends on the eye.

Trabeculectomy may:

• Achieve a lower pressure
• Require fewer medications
• Be preferred in an unoperated eye with healthy conjunctiva

A tube may:

• Be more successful after previous surgery
• Be preferred with conjunctival scarring
• Have fewer early postoperative complications
• Be preferable in certain secondary glaucomas

Is MIGS Better Than Trabeculectomy?

MIGS generally offers:

• Faster recovery
• Less intensive postoperative management
• Lower risk of severe hypotony
• Preservation of the conjunctiva

Trabeculectomy generally offers:

• Greater pressure reduction
• A better chance of reaching very low targets
• Greater medication independence in advanced disease

Can I Have MIGS Without Cataract Surgery?

Some MIGS procedures can be performed alone.

Others are most commonly used or approved with cataract surgery.

Can I Have Cataract Surgery After Trabeculectomy?

Yes.

The surgeon should take steps to protect the bleb and minimise inflammation.

Can I Have Trabeculectomy After MIGS?

Yes.

Most angle-based MIGS procedures preserve the conjunctiva and do not prevent later trabeculectomy or tube surgery.

Can I Have a Tube After Trabeculectomy?

Yes.

Tube surgery is commonly performed after a failed trabeculectomy.

Can I Have Trabeculectomy After a Tube?

Possibly.

The available healthy conjunctiva and the position of the tube plate must be assessed.

Can a Tube Be Replaced?

Yes.

A tube may be:

• Revised
• Repositioned
• Shortened
• Extended
• Exchanged
• Removed

Will I Still Need Glaucoma Drops?

Possibly.

Some patients become medication-free.

Others require one or more drops to reach the target.

Will I Need Another Operation Later?

Possibly.

Glaucoma is lifelong, and the effect of surgery may diminish.

Can Both Eyes Be Operated on Together?

Major filtering or tube surgery is usually staged so that:

• The first eye can be monitored
• Simultaneous bilateral complications are avoided
• The patient retains useful vision during early recovery

Can Surgery Be Performed Under Local Anaesthesia?

Yes.

Many operations are performed with local anaesthesia and sedation.

General anaesthesia may be used for:

• Children
• Severe anxiety
• Inability to lie still
• Tremor
• Complex surgery
• Certain medical or communication needs

Can Glaucoma Surgery Cause Blindness?

Severe permanent visual loss is uncommon but possible.

Potential causes include:

• Infection
• Major bleeding
• Persistent hypotony
• Corneal failure
• Retinal complications
• Uncontrolled inflammation
• Progression of advanced glaucoma
• Another unrelated eye disease

How Often Will I Be Reviewed?

After trabeculectomy, reviews may be required:

• The next day
• Within the first week
• Weekly or more frequently during early healing
• At progressively longer intervals when stable

Long-term glaucoma reviews continue even after the surgical result has stabilised.

When to Seek Urgent Eye Care

Seek urgent assessment for:

• Severe or increasing eye pain
• Rapidly worsening vision
• Increasing redness
• Thick discharge
• Marked light sensitivity
• Severe headache
• Nausea or vomiting
• A sudden shower of floaters
• New flashes
• A curtain or shadow
• Sudden double vision
• Fluid leaking continuously from the eye
• Trauma to the operated eye
• A white or cloudy filtering bleb
• Exposure of a drainage tube

These symptoms may indicate:

• Infection
• A severe pressure rise
• Hypotony
• Choroidal haemorrhage
• Retinal tear or detachment
• Bleb leak
• Tube exposure
• Another ocular emergency

A Glaucoma Surgery Checklist

Information to Report

• All glaucoma medications
• Previous laser treatment
• Previous glaucoma operations
• Cataract surgery
• Retinal surgery
• Corneal transplantation
• Uveitis
• Eye trauma
• Medication allergies
• Asthma
• Heart disease
• Diabetes
• Autoimmune disease
• Blood-thinning medication
• Problems using postoperative drops

Tests That May Be Required

• Visual acuity
• Refraction
• Eye-pressure measurement
• Gonioscopy
• Corneal-thickness measurement
• Optic-nerve examination
• OCT imaging
• Visual-field testing
• Corneal endothelial assessment
• Anterior-segment imaging
• Dilated retinal examination

Questions to Ask the Surgeon

• What type of glaucoma do I have?
• How advanced is the disease?
• What is my target pressure?
• Why is surgery being recommended now?
• What happens if I delay surgery?
• Which operation is recommended?
• Why is this procedure preferred over the alternatives?
• How low is the pressure expected to go?
• How likely am I to remain on drops?
• Will cataract surgery be combined?
• Will mitomycin C be used?
• Will I have a filtering bleb?
• Could I need suture lysis or needling?
• What are the main complications in my eye?
• How frequently will I be reviewed?
• When can I return to work?
• When can I drive?
• What symptoms require urgent assessment?
• What is the next option if this operation fails?

The Bottom Line

Glaucoma surgery lowers intraocular pressure to reduce the risk of further optic-nerve damage.

The principal options include:

• Trabeculectomy
• Glaucoma drainage implants
• Subconjunctival microshunts
• Angle-based minimally invasive glaucoma surgery
• Deep sclerectomy and canaloplasty
• Cyclophotocoagulation
• Combined cataract and glaucoma surgery

Trabeculectomy:

• Can achieve very low pressures
• Is useful in advanced glaucoma
• Requires intensive postoperative management
• May require suture lysis, injections or needling
• Carries bleb-related and hypotony risks

Tube-shunt surgery:

• Is useful after previous eye surgery
• Is suitable for many secondary glaucomas
• May have fewer early complications than trabeculectomy
• Carries risks of tube exposure, corneal damage and double vision

MIGS:

• Usually offers faster recovery
• May reduce pressure and medication burden
• Often preserves the conjunctiva
• Is commonly used in mild-to-moderate open-angle glaucoma
• May be insufficient when a very low target pressure is required

Subconjunctival microshunts:

• Create a filtering bleb
• May offer a more standardised procedure
• Can still scar or require needling
• May not lower pressure as much as trabeculectomy in some patients

No glaucoma operation is risk-free or guaranteed to last indefinitely.

The correct choice depends on:

• Glaucoma mechanism
• Disease severity
• Rate of progression
• Target pressure
• Previous surgery
• Cataract status
• Corneal and conjunctival health
• Patient priorities
• Ability to attend postoperative reviews

The most important message is:

The best glaucoma operation is not necessarily the newest or least invasive procedure. It is the operation most likely to achieve a pressure low enough to protect that patient’s remaining vision, while maintaining an acceptable balance between surgical risk, recovery, medication burden and long-term follow-up.

References

1. Gedde SJ, Feuer WJ, Lim KS, et al. Treatment outcomes in the Primary Tube Versus Trabeculectomy Study after 5 years of follow-up. Ophthalmology. 2022;129(12):1344–1356. PMID: 35835337.
2. Gedde SJ, Schiffman JC, Feuer WJ, et al. Treatment outcomes in the Tube Versus Trabeculectomy Study after five years of follow-up. Am J Ophthalmol. 2012;153(5):789–803.e2. PMID: 22245458.
3. Gedde SJ, Feuer WJ, Lim KS, et al. Postoperative complications in the Primary Tube Versus Trabeculectomy Study during 5 years of follow-up. Ophthalmology. 2022. PMID: 35835336.
4. Gedde SJ, Herndon LW, Brandt JD, et al. Postoperative complications in the Tube Versus Trabeculectomy Study during five years of follow-up. Am J Ophthalmol. 2012;153(5):804–814.e1. PMID: 22244522.
5. Swaminathan SS, et al. Visual field outcomes in the Primary Tube Versus Trabeculectomy Study. Ophthalmology. 2024;131(10):1157–1163. PMID: 38582154.
6. Christakis PG, Kalenak JW, Tsai JC, et al. Five-year treatment outcomes in the Ahmed Baerveldt Comparison Study. Ophthalmology. 2016. PMID: 25439606.
7. Christakis PG, Zhang D, Budenz DL, et al. The Ahmed Versus Baerveldt Study: five-year treatment outcomes. Ophthalmology. 2016. PMID: 27544023.
8. Christakis PG, Zhang D, Budenz DL, et al. Five-year pooled data analysis of the Ahmed Baerveldt Comparison Study and Ahmed Versus Baerveldt Study. Am J Ophthalmol. 2017;176:118–126. PMID: 28104418.
9. Singh K, Mehta K, Shaikh NM, et al. Trabeculectomy with intraoperative mitomycin C versus 5-fluorouracil: prospective randomised clinical trial. Ophthalmology. 2000;107(12):2305–2309. PMID: 11097613.
10. De Fendi LI, Arruda GV, Scott IU, Paula JS. Mitomycin C versus 5-fluorouracil as an adjunctive treatment for trabeculectomy: meta-analysis of randomised clinical trials. Clin Exp Ophthalmol. 2013;41(8):798–806. PMID: 24308066.
11. Ahmed IIK, Rhee DJ, Jones J, et al. Long-term outcomes from the HORIZON randomised trial for a Schlemm’s canal microstent in combined cataract and glaucoma surgery. Ophthalmology. 2022. PMID: 35218867.
12. Montesano G, et al. Five-year visual-field outcomes of the HORIZON trial. Am J Ophthalmol. 2023. PMID: 36813144.
13. Gaskin JCF, Bigirimana D, Kong GYX, et al. Prospective randomised trial of cataract surgery versus combined cataract surgery with iStent Inject. Ophthalmol Glaucoma. 2024;7(4):326–334. PMID: 38369058.
14. Sheybani A, Dick HB, Ahmed IIK. Gel stent versus trabeculectomy: the randomised multicentre Gold-Standard Pathway Study. Am J Ophthalmol. 2023. PMID: 36972738.
15. Baker ND, Barnebey HS, Moster MR, et al. Ab externo MicroShunt versus trabeculectomy in primary open-angle glaucoma: one-year results from a randomised multicentre study. Ophthalmology. 2021. PMID: 34051211.
16. Baker ND, et al. Ab externo MicroShunt versus trabeculectomy: two-year results from a randomised multicentre study. Ophthalmology. 2023. PMID: 37769852.
17. Yip VCH, Lee DMX, Acosta PO, et al. Efficacy and safety of the PreserFlo MicroShunt in Asian patients with glaucoma: two-year results. J Glaucoma. 2026;35(1):23–33. PMID: 41370652.
18. Ayyala RS, Chaudhry AL, Okogbaa CB, Zurakowski D. Comparison of surgical outcomes between canaloplasty and trabeculectomy. Ophthalmology. 2011.
19. Matlach J, Dhillon C, Hain J, et al. Trabeculectomy versus canaloplasty in open-angle glaucoma: a prospective randomised clinical trial. Acta Ophthalmol. 2015. PMID: 25847610.
20. El Sayyad F, Helal M, El-Kholify H, Khalil M, El-Maghraby A. Non-penetrating deep sclerectomy versus trabeculectomy in bilateral primary open-angle glaucoma. Ophthalmology. 2000;107(9):1671–1674. PMID: 10964827.
21. Shaarawy T, Nguyen C, Schnyder C, Mermoud A. Deep sclerectomy with and without a collagen implant: long-term randomised follow-up. Br J Ophthalmol. 2004;88(1):95–98. PMID: 14693783.
22. Vold S, Ahmed IIK, Craven ER, et al. Two-year COMPASS trial results: supraciliary microstenting with cataract surgery for open-angle glaucoma. Ophthalmology. 2016.
23. Pfeiffer N, Garcia-Feijoo J, Martinez-de-la-Casa JM, et al. A randomised trial of a Schlemm’s canal microstent with cataract surgery for reducing intraocular pressure. Ophthalmology. 2015.
24. Coulon SJ, Vanner EA, Gedde SJ. Outcomes of glaucoma reoperations in the Primary Tube Versus Trabeculectomy Study. Ophthalmol Glaucoma. 2023;6(4):422–431. PMID: 36828230.
25. Gedde SJ, Schiffman JC, Feuer WJ, et al. Outcomes of glaucoma reoperations in the Tube Versus Trabeculectomy Study. Am J Ophthalmol. 2014. PMID: 24531027.