Lens surgery

Cataract
and glaucoma

When glaucoma and a cataract coexist, surgery on the lens also makes it possible to act on the drainage of aqueous humour, and the choice of implant takes the glaucoma into account. A micro-stent can be added during the same procedure.

The lens and cataract →

01 — Understanding

How it works

Aqueous humour is the fluid that fills the front of the eye. It drains mainly through the trabecular meshwork, a microscopic filter located in the angle between the cornea and the iris. It then reaches Schlemm’s canal, a fine circular channel that returns it to the venous circulation. In open-angle glaucoma, the resistance of this filter increases.

The iStent inject is a titanium implant less than half a millimetre in size. Two stents are inserted through the trabecular meshwork and open a direct passage into Schlemm’s canal. It belongs to the MIGS family (minimally invasive glaucoma surgery), performed from inside the eye through the same incisions as those used for cataract surgery, without opening the conjunctiva.

The iridocorneal angle and the trabecular micro-stent Enlarged cross-section of the angle between the cornea and the iris: in open-angle glaucoma, aqueous humour struggles to pass through the trabecular meshwork; a micro-stent opens a direct passage into Schlemm’s canal. The iridocorneal angle and the trabecular micro-stent Enlarged cross-section of the angle between the cornea and the iris, where aqueous humour leaves the eye Orientation Open-angle glaucoma With a trabecular micro-stent Cross-section of the anterior segment; the frame marks the area enlarged opposite. Aqueous humour outflow Slowed passage through the trabecular meshwork Trabecular meshwork (open-angle glaucoma) Micro-stent (generic representation) 100 µm; simplified proportions Cornea Sclera To the episcleralveins Collector channel Schlemm’s canal Trabecular meshwork Anterior chamber(aqueous humour) Iris Ciliarybody Micro-stent The meshwork offers more resistance:aqueous humour drains less easily. The micro-stent crosses the meshwork andopens a direct passage into the canal. Aqueous humour leaves the eye through the trabecular meshwork, Schlemm’s canal and the collector channels, before reaching the episcleral veins on the surface of the eye. The micro-stent bypasses the resistance of the trabecular meshwork; the rest of the pathway, up to the episcleral veins, is unchanged.
The iridocorneal angle and the trabecular micro-stent
02 — Combined surgery

Combined
surgery

When glaucoma (or ocular hypertension) and a cataract coexist, surgery on the lens also makes it possible to act on the drainage of aqueous humour. For most of my glaucoma patients undergoing cataract surgery, I suggest combining it with a trabecular micro-stent (iStent) during the same procedure. This addition complements glaucoma treatment. It does not replace follow-up, nor, in every case, eye drops.

Who is it for?

As a general rule, I offer it in mild to moderate open-angle glaucoma, for a patient already treated with eye drops who needs cataract surgery.

I do not place it in the following situations:

  • advanced glaucoma requiring a very low target pressure, which is better addressed by filtering surgery;
  • glaucoma secondary to neovascularisation or inflammation (uveitis);
  • an angle which, when examined during the procedure, does not allow the stents to be placed in good conditions.

Angle-closure glaucoma is discussed case by case. Cataract surgery widens the angle on its own, and the benefit of an additional stent is assessed individually.

Realistic expectations

Cataract surgery on its own often lowers intraocular pressure. The stent adds a further effect, which often allows patients to reduce their pressure and/or the number of eye drops they use. This effect has a physiological limit: aqueous humour must then pass through the veins in the wall of the eye, whose pressure sets a floor. This is why the iStent is suited to early to moderate glaucoma, and not to situations where a very low pressure is required.

No result is guaranteed. Some patients keep the same treatment; others may be able to reduce part of it. Glaucoma remains a chronic disease.

Why the effect of a micro-stent remains moderate Hydraulic analogy: the micro-stent lowers the pressure in the eye by bypassing the trabecular meshwork, but cannot bring it below the pressure of the episcleral veins. Why the effect of a micro-stent remains moderate A hydraulic analogy: the pressure in the eye cannot fall below that of the veins into which aqueous humour drains How to read it Open-angle glaucoma With a trabecular micro-stent The eye produces aqueous humour continuously. Its pressure depends on how easily it drains away. It cannot fall below the pressure of the veins into which it drains. Pressure in the eye (water height) Trabecular meshwork: main resistance Collector channels: downstream resistance Micro-stent: bypass of the meshwork Floor: episcleral venous pressure Share of pressure due to resistance venous floor Continuous production Meshwork Collector channels Episcleralveins Eye venous floor Micro-stent The meshwork offers more resistance: the levelrises well above the floor. The stent bypasses the meshwork: the levelfalls, but stays above the floor. The micro-stent removes part of the resistance, without acting on the collector channels or on venous pressure: its effect is therefore moderate. Going below this floor requires another drainage route: this is the principle of filtering surgery, considered in more advanced glaucoma.
Why the effect of a micro-stent remains moderate

The procedure

  1. Cataract surgery and lens implantation, in the usual way.
  2. Filling the front of the eye with a viscoelastic gel and viewing the angle through a gonioscopy lens (a mirrored lens placed on the cornea that makes the angle visible).
  3. Inserting the stents through the trabecular meshwork.
  4. Checking their position and removing the gel.

The stent adds a few minutes to cataract surgery. Slight bleeding in the front of the eye is common: it can blur vision for the first few days and clears on its own. Otherwise, recovery is comparable to that after cataract surgery alone. Complications specific to the stent are rare: displacement, blockage or a temporary pressure spike.

03 — Choosing the implant

Choosing
the implant

Glaucoma can reduce contrast sensitivity and the visual field. Diffractive multifocal IOLs, which split light between several focal points, also reduce contrast sensitivity: I avoid them in glaucoma. Depending on the stage, I favour a monofocal IOL. Extended depth of focus (EDOF) IOLs can be considered in early, stable forms. Because glaucoma is a progressive disease, the choice must also take into account vision in ten or twenty years’ time, not just the immediate result.

Implant choice is covered in detail in a dedicated article: “Choosing your implant: from presbyopia to refractive cataract surgery”.

04 — Narrow angle

Narrow angle
and lens surgery

The crystalline lens grows slowly throughout life. As it thickens, it pushes the iris forward and reduces the space in the angle through which aqueous humour drains. In some people, this angle becomes narrow, or even closes intermittently. This is more common in short eyes, and therefore in hyperopic eyes, and it becomes more pronounced with age.

How is it detected?

A narrow angle usually causes no symptoms. It is found on examination, by looking directly at the angle through a gonioscopy lens, sometimes supplemented by imaging of the anterior segment (the front part of the eye, from the cornea to the lens). More rarely, it shows itself through episodes of blurred vision with coloured haloes and intense eye pain, which call for an urgent consultation.

What replacing the lens changes

Replacing a crystalline lens more than four millimetres thick with an implant less than one millimetre thick deepens the anterior chamber (the fluid-filled space between the cornea and the iris) and reopens the angle. This is a direct mechanical effect, now recognised as a treatment for angle closure, and not a side benefit of cataract surgery.

This applies to two different situations:

  • a patient in whom a narrow angle has been identified, and for whom lens surgery is being discussed for that reason, together with their usual ophthalmologist;
  • a patient considering lens surgery for their vision, whether for cataract or refractive lens exchange, whose assessment shows a narrow angle. The procedure then addresses both questions at once.

The limits

Reopening the angle does not repair damage that has already occurred. If the optic nerve has been damaged, that damage is permanent and follow-up remains necessary. Where adhesions have formed between the iris and the angle, reopening is only partial, and raised pressure may persist.

Laser iridotomy (a small opening made in the iris to ease the flow of aqueous humour) also keeps its place, particularly in an emergency or when lens surgery is not indicated.

Finally, the state of the angle alone is not enough to justify removing a clear lens in a young patient with no visual symptoms. The indication is decided case by case, with the ophthalmologist who monitors the pressure and visual field.

05 — Follow-up

After
the procedure

Glaucoma follow-up remains with your usual ophthalmologist, who adjusts treatment according to changes in pressure and visual field.

Reimbursement

The iStent is covered by compulsory health insurance (INAMI, Belgium’s national health insurance). As it is a device with its own INAMI billing code, the remaining out-of-pocket cost is usually covered by hospitalisation insurance, depending on the terms of your policy. The exact amount and the procedure fees are provided at your consultation.

Lens surgery, its implants and its special cases

The lens and cataract →
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