By Dr Sherif Ekram, Consultant Ophthalmic Surgeon (Glaucoma and Refractive Surgery, CertLRS)
Quick answer: MIGS (minimally invasive glaucoma surgery) is a group of procedures that lower eye pressure through tiny incisions, with faster recovery than traditional glaucoma surgery. iStent Inject suits mild to moderate open-angle glaucoma, usually at the time of cataract surgery. GATT opens the eye’s natural drainage channel all the way round and suits moderate open-angle glaucoma. Preserflo MicroShunt creates a new drainage route and suits moderate to advanced glaucoma that needs a lower target pressure. The right choice depends on how advanced the glaucoma is, the pressure your optic nerve can tolerate, and whether you also need cataract surgery.
What is MIGS?
Glaucoma damages the optic nerve, most often because fluid inside the eye does not drain well enough and pressure builds up. Drops and laser are the first line of treatment. When they are not enough, not tolerated, or not used reliably, surgery becomes the safer option for the long term.
For decades, surgery meant trabeculectomy or a large drainage tube. Both work well, but recovery is longer and they need close follow-up. Minimally invasive glaucoma surgery (MIGS) sits between drops and these bigger operations. The procedures share three features: small incisions, a high safety profile, and quick visual recovery. The trade-off is that most MIGS lower pressure less than a trabeculectomy, so case selection matters.
iStent Inject: a micro-bypass for early to moderate glaucoma
The iStent Inject is one of the smallest implants used in medicine. Two tiny titanium stents are placed in the eye’s natural drainage meshwork (the trabecular meshwork), creating a bypass so fluid reaches the collecting channels more easily.
- Best suited to: mild to moderate open-angle glaucoma, especially in patients who also need cataract surgery.
- Main benefit: it adds very little time or risk to a routine cataract operation and can reduce the number of drops needed.
- Limitation: the pressure reduction is modest. It is not designed for advanced glaucoma or very low target pressures.
GATT: reopening the whole drainage channel
GATT (gonioscopy-assisted transluminal trabeculotomy) is an implant-free procedure. Working from inside the eye, the surgeon threads a fine microcatheter or suture through Schlemm’s canal, the eye’s circular drainage channel, and opens it through 360 degrees. Fluid can then drain through the eye’s own outflow system.
- Best suited to: moderate open-angle glaucoma, including pseudoexfoliation and pigmentary glaucoma, either alone or combined with cataract surgery.
- Main benefit: no implant is left behind and no bleb (the blister of fluid created by trabeculectomy) is formed, so long-term bleb problems are avoided.
- What to expect: a small bleed inside the eye (hyphaema) is common in the first days and usually clears on its own. Vision may be blurred for a week or two.
GATT needs a clear view of the drainage angle and practised gonioscopic technique. Dr Ekram lectures on where GATT fits in the surgical pathway, and the procedure is one of the most frequent topics clinicians raise with him at international meetings.
Preserflo MicroShunt: a lower target pressure without a full trabeculectomy
The Preserflo MicroShunt is a soft 8.5 mm tube that drains fluid from the front of the eye to a small reservoir under the conjunctiva. It is placed from outside the eye with an anti-scarring medicine (mitomycin C) and creates a controlled bleb.
- Best suited to: moderate to advanced glaucoma, or patients whose optic nerve needs a low target pressure.
- Main benefit: pressure reduction closer to trabeculectomy, with a more standardised and less invasive operation.
- What to expect: more frequent check-ups in the first weeks, as with any bleb-forming surgery, and occasional needling if scarring starts.
MIGS at a glance
| iStent Inject | GATT | Preserflo MicroShunt | |
|---|---|---|---|
| Glaucoma stage | Mild to moderate | Moderate | Moderate to advanced |
| Pressure lowering | Modest | Moderate | Greater |
| Implant left in eye | Yes (micro-stents) | No | Yes (micro-tube) |
| Bleb formed | No | No | Yes |
| Combined with cataract surgery | Usually | Often | Sometimes |
When MIGS is not enough: tubes and complex reconstruction
Some eyes need more than MIGS. Glaucoma after previous failed surgery, neovascular or uveitic glaucoma, and eyes with extensive scarring often need a glaucoma drainage device. Non-valved tubes such as the ClearPath GDD drain fluid to a plate placed further back on the eye and can achieve low pressures where other operations have failed.
Complex glaucoma also overlaps with lens problems. Aqueous misdirection, for example, may need an irido-zonulo-hyaloido-vitrectomy (IZHV), and an unstable or dislocated lens may need a scleral-fixated IOL or IOL exchange. Having both glaucoma and anterior segment skills in one surgeon means these problems can be planned together rather than treated in separate stages.
How Dr Ekram chooses the right glaucoma operation
Choosing a procedure is less about the device and more about the eye. Dr Ekram’s assessment covers:
- Target pressure: how low the pressure must be to protect the remaining optic nerve, based on visual fields and OCT scans.
- Type of glaucoma: open-angle, angle-closure, pseudoexfoliation, secondary glaucoma.
- Cataract status: if a cataract is present, combining procedures can mean one recovery instead of two.
- Drop burden and tolerance: allergy, ocular surface disease and difficulty using drops all favour surgery sooner.
- Lifestyle and follow-up: bleb surgery needs close early follow-up, which matters for patients who travel or live far from the clinic.
With more than 3,000 glaucoma operations performed, from iStent Inject and GATT to Preserflo and non-valved tubes, Dr Ekram can offer the procedure that fits the eye rather than the one a surgeon happens to perform. On combined cataract and glaucoma lists, careful theatre planning also keeps these longer cases safe and on time.
Frequently asked questions
Is MIGS a cure for glaucoma?
No. Glaucoma damage cannot be reversed. MIGS lowers eye pressure to slow or stop further damage, and many patients still need regular monitoring and sometimes drops after surgery.
Is MIGS available in the UK?
Yes. iStent Inject, GATT and Preserflo MicroShunt are all performed in the UK, both in the NHS and privately. Availability varies by hospital and surgeon.
How long is recovery after MIGS?
Most patients return to light daily activities within a few days. Recovery after GATT or Preserflo can take a little longer than after iStent, mainly because of short-term blurring or more frequent early check-ups.
Can MIGS be done at the same time as cataract surgery?
Often, yes. iStent Inject and GATT are commonly combined with cataract surgery, which means one operation and one recovery period.
How do I know if my surgeon is experienced in glaucoma surgery?
Ask how many of the specific procedure they perform, how they manage complications, and whether they offer the full range from MIGS to tubes. Our guide to choosing an eye surgeon in the UK lists the questions worth asking.
About the author
Dr Sherif Ekram is a Consultant Ophthalmic Surgeon in the UK with over 18 years of surgical experience, dual-subspecialised in glaucoma and refractive surgery and holder of the Royal College of Ophthalmologists’ Certificate in Laser and Refractive Surgery (CertLRS). He has performed more than 3,000 glaucoma operations, has served as Glaucoma Clinical Lead, and is an RCOphth-approved surgical trainer. More guides are available in the articles library.
This article is for general information and does not replace a personal consultation. Treatment decisions depend on a full examination.
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