Filtration surgery creates a new drainage channel to lower eye pressure and protect the optic nerve in glaucoma. Learn how filtration surgery works, who it suits, and what to expect during recovery.
Filtration surgery is a group of glaucoma operations that create a new controlled drainage pathway for the eye’s natural fluid (aqueous humour) to leave the eye.
By increasing outflow, eye pressure (intraocular pressure — IOP) is lowered, which helps protect the optic nerve from further damage caused by glaucoma.
The most well-known type of filtration surgery is trabeculectomy, but the term also includes newer filtration procedures such as:
Preserflo MicroShunt
Aqueous shunt implants (tubes)
All filtration surgeries aim to achieve low and stable eye pressure, especially in moderate to advanced glaucoma where drops, SLT, or MIGS no longer provide adequate control.
Local anaesthetic is used to keep the eye comfortable throughout the procedure.
A small filtering channel is created under the upper eyelid.
Fluid drains through this channel to form a bleb — a tiny reservoir hidden beneath the eyelid.
Special anti-scarring medication (Mitomycin-C or 5-FU) is used to prevent the drainage pathway from closing.
The drainage rate can be fine-tuned with sutures to achieve the desired pressure.
Depending on the specific technique, the surgery may use:
A scleral flap (traditional trabeculectomy)
A micro-shunt device (Preserflo)
A drainage tube (Ahmed or Baerveldt implant)
All of them serve the same purpose: reducing IOP to protect sight.
Achieves very low eye pressures — often lower than drops or MIGS can achieve
Strong long-term pressure control
Reduces or eliminates the need for glaucoma drops
Protects against progressive optic nerve damage
Effective for moderate and advanced glaucoma
Suitable when other treatments have failed
Adaptable — can be combined with other procedures if needed
For patients with fast-progressing disease, filtration surgery is often the most effective intervention.
Your ophthalmologist may recommend filtration surgery if you have:
Open-Angle Glaucoma not controlled by medication
Advanced glaucoma requiring aggressive pressure lowering
Ocular Hypertension with optic nerve changes
Poor tolerance or allergy to multiple eye drops
Angle-closure glaucoma needing long-term filtration
Secondary glaucoma (steroid-induced, uveitic, traumatic)
Progression despite SLT or MIGS
It is typically recommended when less invasive options are insufficient.
Local anaesthetic numbs the eye completely
The procedure takes 30–45 minutes
A small lid speculum keeps the eye gently open
You will go home the same day
Vision may be blurred initially due to inflammation
A protective shield is worn overnight
Frequent early follow-ups allow the surgeon to optimise healing
In the first weeks, minor adjustments — such as suture release, bleb massage, or 5-FU injections — may be required to maintain ideal drainage.
Early intervention may be important if:
Visual fields show progressive loss
The optic nerve is deteriorating rapidly
Medication is no longer effective
You require pressure levels in the low teens or single digits
You’re intolerant to drops
You’re developing structural progression on OCT scans
The sooner pressure stabilises, the better the long-term visual outcome.
Expect redness, irritation, and blurred vision for several weeks
Use anti-inflammatory and antibiotic drops for 6–8 weeks
Avoid heavy lifting, bending, and eye rubbing
Keep water, dust, and sweat away from the eye
Monitor for signs of over- or under-filtration
Attend all scheduled follow-ups — early healing determines long-term success
With proper post-operative care, filtration surgery provides long-lasting pressure control.
