Glaucoma

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)

Clinical presentation

Closed-angle glaucoma

• 1/3 present as an emergency - acute red eye and visual loss with headache and N+V (see Acute Closed Angle Glaucoma notes)

• Signs: red eye, cloudy cornea, dilated pupil

• Can lose sight very quickly

Open-angle glaucoma

• Usually asymptomatic

• Screened for by optometrists

• Visual field defect

• May or may not have high IOP

Investigations

Fundoscopy

• Cupped disc (increased cup-to-disc ratio) indicates a reduced volume of healthy neuro-retinal tissue, which can occur in glaucoma
• Raised intraocular pressure damages the optic disc and nerve
• The edges of the disc become rolled up and the centre becomes depressed

• A pale optic disc suggests the presence of optic atrophy, which can result from advanced glaucoma

Management

Primary open angled glaucoma

• Glaucoma drops work by either decreasing aqueous production or increasing drainage

• Prostanoids e.g. latanoprost ('xalatan') - first line

• Second line - β blockers, carbonic anhydrase inhibitors

• Others - ⍺2 adrenergic agonist, parasympathomimetics, combination eyedrops (e.g. cosopt - dorxolamide and timolol)

Closed-angle glaucoma

• In acute presentation need to lower IOP quickly with drops/oral medication to prevent the patient from going blind e.g. pilocarpine 4% eye drops

• Definitive management - laser peripheral iridotomy