Glaucoma, in 3D

1 · The healthy eye

A fluid in balance

The eye constantly produces a clear fluid, the aqueous humour: it is made behind the iris, passes through the pupil and nourishes the cornea and the lens.

A drain that works

It leaves through the trabecular meshwork into Schlemm’s canal. Pressure reflects the balance between production and outflow; a single number does not by itself determine whether glaucoma is present.

2 · Glaucoma

The filter fails

In the most common form of glaucoma the angle is open, but the meshwork filters worse than it should. Aqueous builds up inside the eye.

Pressure can rise silently

Raised pressure usually causes no pain or early symptoms. Glaucoma can also occur at pressures within the usual statistical range, so the nerve and visual function must be assessed.

3 · Optic nerve damage

The damage is in the nerve

Glaucoma causes progressive loss of optic-nerve fibres. Pressure is the main modifiable factor, but each nerve has a different susceptibility.

The visual field narrows

An arc of vision above or below the centre is lost, and the eye compensates so it goes unnoticed.

What is lost cannot be recovered

In advanced stages the visual field can become severely restricted. Lowering pressure reduces the risk of progression; the target and treatment are individualised.

4 · SLT laser

Laser in the clinic

SLT trabeculoplasty is done without an operating theatre, with anaesthetic drops: a contact lens on the cornea lets the surgeon see inside the angle and focus on the trabecular meshwork.

Applications to the trabecular meshwork

Low-energy pulses are distributed over the pigmented meshwork. The biological response aims to improve drainage without an incision.

Drainage may improve

Pressure may fall over the following weeks. The magnitude and duration vary; drops, repeat laser or another option may still be needed.

5 · XEN implant

A gel stent through a 2 mm incision

The XEN implant enters through a corneal micro-incision: a 6 mm gel tube that crosses the wall of the eye and softens as it hydrates.

It drains under the conjunctiva

Aqueous forms a filtering bleb under the conjunctiva. This surgery requires follow-up and may need later adjustments; in some cases it is combined with cataract surgery.

6 · Deep sclerectomy

Non-penetrating filtering surgery

In deep sclerectomy a scleral flap is created and a deeper layer is removed, leaving a thin membrane through which filtration is intended to occur.

Filtration beneath the conjunctiva

Aqueous is reabsorbed beneath the conjunctiva. As a non-penetrating technique it has a different profile from trabeculectomy, but it still carries risks and requires close review.