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PH-SE01

Glaucoma

How aqueous humour is made and drained, why impaired drainage raises eye pressure, how the optic nerve head is damaged and why vision is lost silently from the periphery, and how acute angle closure differs.

By the end, you can

  • Trace the production and drainage of aqueous humour and its role in intraocular pressure.
  • Distinguish open-angle from angle-closure glaucoma by where drainage fails.
  • Explain how pressure and poor blood flow damage retinal ganglion cell axons at the optic disc.
  • Explain why field loss begins in the periphery and is noticed late.
  • Relate the features of acute angle closure to its mechanism.
  • Recognise the classic disc and field changes, pressure values and tests of glaucoma, and explain how prostaglandin analogues, beta-blockers, carbonic anhydrase inhibitors, laser and surgery lower intraocular pressure.

What it is

Glaucoma is a group of eye diseases in which retinal ganglion cells and their axons are progressively lost, producing characteristic cupping of the optic disc and a matching loss of visual field. Raised intraocular pressure is the main modifiable risk factor, but glaucoma can occur at normal pressures and raised pressure does not always cause it.

3 types to tell apart
Primary open-angle glaucoma
The drainage angle is open but resists outflow; pressure rises slowly and damage is painless. The commonest type in people of European and African ancestry.
Angle-closure glaucoma
The iris blocks the drainage angle. It can be chronic or sudden (acute angle closure), and is more common in people of East Asian ancestry and in long-sighted eyes.
Normal-tension and secondary glaucoma
Damage at statistically normal pressure, or glaucoma caused by another condition such as inflammation, steroid use or new vessels in the angle.

Normal function

Making and draining aqueous humour

The , behind the , secretes clear aqueous humour, which nourishes the avascular and . It flows forwards through the pupil into the .

It drains at the iridocorneal angle, where the iris meets the cornea near the : through a sieve-like trabecular meshwork into Schlemm’s canal and on to the veins, with a smaller route through the ciliary muscle.

The balance between production and drainage sets the intraocular pressure, normally about 10–21 mmHg, which keeps the eye’s shape. At the back of the eye, about a million retinal ganglion cell axons converge at the optic disc and leave through a perforated plate of tissue, the lamina cribrosa, to form the optic nerve.

Point to it on the model