Ophthalmology - acute angle closure glaucoma Flashcards
What is glaucoma?
Optic nerve damage caused by raised intracranial pressure
What causes the raised ICP in glaucoma?
The raised intraocular pressure is caused by a blockage in aqueous humour trying to escape the eye.
Pathophysiology of acute angle-closure glaucoma
iris bulges forward and seals off the trabecular meshwork from the anterior chamber preventing aqueous humour from being able to drain away.
Risk factors for acute angle-closure glaucoma
Increasing age
Females are affected around 4 times more often than males
Family history
Chinese and East Asian ethnic origin. Unlike open-angle glaucoma, it is rare in people of black ethnic origin.
Shallow anterior chamber
Hypermetropia
What medications can precipitate acute angle-closure glaucoma?
Adrenergic medications such as noradrenalin
Anticholinergic medications such as oxybutynin and solifenacin
Tricyclic antidepressants such as amitriptyline, which have anticholinergic effects
How does acute-angle closure glaucoma present?
Severely red painful eye
Blurred vision
Halos around lights
Photophobia
Associated headache, nausea and vomiting
Signs of acute-angle closure glaucoma on examination
Red-eye Teary Hazy cornea Decreased visual acuity Dilatation of the affected pupil Fixed pupil size Firm eyeball on palpation
Management of acute angle closure glaucoma
Lie the patient flat
Medications to reduce IOP:
Pilocarpine eye drops (2% blue eyes, 4% for brown)
Acetazolamide (oral or IV)
Hyperosmotic agents e.g. glycerol, mannitol
Timolol
Brimonidine
The definitive treatment is laser iridotomy - other treatments are only for temporary relief
How do these medications reduce IOP
Glycerol/mannitol
Timolol
Brimonidine
Glycerol/mannitol - increase the osmotic gradient between the blood and the fluid in the eye
Timolol - reduce the production of aqueous humour
Brimonidine - a sympathomimetic that reduces the production of aqueous fluid and increase uveoscleral outflow
How does pilocarpine reduce IOP
It acts on the muscarinic receptors in the sphincter muscles in the iris and causes constriction of the pupil. Therefore it is a miotic agent. It also causes ciliary muscle contraction. These two effects cause the pathway for the flow of aqueous humour from the ciliary body, around the iris and into the trabecular meshwork to open up.
What is Acetazolamide and how does it reduce IOP?
It is a carbonic anhydrase inhibitor. This reduces the production of aqueous humour.
What is laser iridotomy?
The definitive treatment for acute angle-closure glaucoma
It involves using a laser to make a hole in the iris to allow the aqueous humour to flow from the posterior chamber into the anterior chamber.
Itrelieves pressure that was pushing the iris against the cornea and allows the humour the drain.
