Saturday, 26 April 2014

Glaucoma

Glaucoma is listed in the headache syllabus, but no-where else. It's implied in the red eye syllabus.

Epidemiology
- Affects 2% of over 40 years old
 - Up to 10% of those above 80 years.
 - Second most common cause of blindness in the UK 
- Accounts for 10% of registrable blindness.

Pathopysiology
There are two types of glaucoma - open or closed. The "angle" in open-angle glaucoma refers to the angle between the iris and the cornea.

flow of aqueous humour

Closed-angle glaucoma occurs when the iridocorneal angle narrows so much that the aqueous fluid is unable to flow from the posterior to the anterior chamber and cannot reach the trabecular meshwork.

Open-angle glaucoma tends to progress at a slower rate than closed-angle glaucoma, and patients may not realise they have vision loss until there has been irreversible damage to the optic nerve and retinal nerve fibres. Acutely, closed-angle glaucoma is much more important to know about.

Risk factors include:
- history of previous episodes recent use of anticholinergic drugs
- African or Afro-Carribean origin Chinese, Hispanic and Inuit origin
- ocular hypertension (OHT)
- increasing age
- short sightedness (myopia)
- family history
- diabetes

Symptoms
- acute onset of a red and painful eye
- impaired vision
- multicoloured haloes (like a rainbow) forming around lights
- nausea, vomiting and headache

The acute attack can be preciptated by:
- topical mydriatics anticholinergic and sympathomimetic drugs
- emotional stimuli
- accommodation (e.g. reading)
- dim light 

Treatment
There are five main drug classes of glaucoma eye drops:
- prostaglandin derivatives beta-blockers carbonic anhydrase inhibitors
- sympathomimetics miotics
- head up at least 30 degrees
- symptomatic treatment of pain and nausea/ vomiting
- discontinue any precipitants and treat underlying causes

It is controversial whether to start treatment in the ED or not. I suspect it depends on transfer time to ophthalmology assessment. Consider opiate analgesia, an antiemetic and acetazolamide 500mg IV then 500mg PO. Treatment with a topical miotic such as pilocarpine 1 or 2% every 5 minutes should be started approximately 1 hour after commencing other measures as initially the pupil is usually paralysed and unresponsive.


References 
http://www.enlightenme.org/knowledge-bank/cempaedia/atraumatic-red-eye
http://www.enlightenme.org/learning-zone/under-pressure 
http://www.enlightenme.org/knowledge-bank/cempaedia/eye-initial-assessment
http://www.ophthobook.com/chapters/glaucoma 
http://learning.bmj.com/learning/module-intro/glaucoma-chronic-open-angle-glaucoma-ocular-hypertension-diagnosis-management-.html?moduleId=10013290&searchTerm=%E2%80%9Cglaucoma%E2%80%9D&page=1&locale=en_GB
http://www.doctors.net.uk/ecme/wfrmNewIntro.aspx?moduleid=1350
http://lifeinthefastlane.com/ophthalmology-befuddler-007-2/

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