A group of chronic diseases characterised by a progressive optic neuropathy resulting in characteristic field defects

Aetiology

• Raised intraocular pressure is currently the only modifiable risk factor
• Increased incidence with age
• Myopia and Afro-Caribbean ethnicity are risk factors

Pathophysiology

• Pressure in the eye is related to the amount of vitreous fluid and anteriorly aqueous humour
• Normally the aqueous fluid drains out through the trabecular meshwork
• Glaucoma occurs when there is a blockage in the drainage through the trabecular meshwork or in the Canal of Schlemm
• Pressure has the biggest consequences for optic disc and optic nerve

Open angled glaucoma

• Result of poor drainage through trabecular meshwork

Closed angle glaucoma

• Drainage through meshwork is patent
• Aqueous humour encounters resistance through iris/lens channel
• Increased pressure gradient causes peripheral iris to bow forward, obstructing trabecular meshwork → pressure increases

Rubeotic glaucoma

• New vessel formation in diabetic eye disease forms obstructive angle (rare and late complication)