Glaucoma Flashcards
Where is aqueous humour made in the eye?
The ciliary body
What is glaucoma?
A pathology where damage is sustained to the optic nerve due to raised intraocular pressure
Where is the aqueous humour stored?
In the anterior and posterior chambers of the eye
What is the pathway of the aqueous humour?
Made by ciliary body
Around lens under iris through anterior chamber, through trabecular meshwork into the canal of schlemm.
Enters general circulation and is reabsorbed into the body
What is a normal intraocular pressure?
10-21mmHg
The pressure is created by resistance to flow through the trabecular meshwork
Pathophysiology of open angle glaucoma?
Gradual increase in resistance through the trabecular meshwork leading to a gradual increase in intraocular pressure.
Pathophysiology of closed angle glaucoma?
Iris bulges forward and seals off trabecular meshwork from the anterior chamber preventing aqueous humour from draining.
This leads to rapid build up in pressure - ophthalmological emergency
Optic disc changes in open angle glaucoma?
Cupping of the optic disc. There is an increase in size of the optic cup compared to the disc. >50% of the size of the disc, this is abnormal.
Risk factors for open angle glaucoma?
Increasing age
Family history
Myopia
Black ethnic origin
Clinical presentation of open angle glaucoma?
Asymptomatic for a long period of time. Usually diagnosed by routine screening.
Peripheral vision affected first - gradual loss of peripheral vision leading to tunnel vision in later stages.
Fluctuating pain
Headaches
Haloes surrounding lights - worse at night time.
How do you measure intraocular pressure?
1) Non-contact tonometry - shooting a puff of air at the cornea and measuring the corneal response to that puff of air. Increased pressure leads to reduced reaction of the cornea.
2) Goldmann applanation tonometry - gold standard method. Device mounted on slip lamp which makes contact with cornea and applies different pressures onto the eye to measure corneal response.
How do we make a diagnosis of glaucoma?
Goldmann applanation tonometry
Fundoscopy
Visual field assessment - check for peripheral vision loss
Medical management of open angle glaucoma?
Treatment started if IO pressure is >24mmHg
1) Prostaglandin analogues - e.g. Latanoprost. This increases uveoscleral outflow.
2) Topical beta blockers (e.g. Timolol - reduce production of humour)
3) carbonic anhydrase inhibitors (e.g. Dorzolamide - reduce production of humour)
4) sympathomimetrics (e.g. Brimonidine - reduce humour production, increase uveoscleral outflow)
Side effects of topical prostaglandins?
Eyelash growth
Eyelid pigmentation
Iris pigmentation (browning of iris)
Surgical procedure for open angle glaucoma?
Trabeculectomy - only if eyedrops are ineffective
New channel from anterior chamber through sclera to a location under the conjunctiva.
A bleb is created where the aqueous humour drains
What is acute angle closure glaucoma?
Iris bulges forward and seals off trabecular meshwork from anterior chamber. This prevents aqueous humour from being able to drain away through the trabecular meshwork.
In closed angle glaucoma, in what anatomical location does aqueous humour increase and worsen the presentation?
In the posterior chamber of the eye behind the iris
What are the risk factors for acute angle closure glaucoma?
Increasing age
Females (4:1)
Family history
Chinese/East Asian ethnic origin
Shallow anterior chamber (anatomical variants)
Medication - e.g. Noradrenaline, anticholinergics and TCA’s.
Clinical presentaiton of acute angle closure glaucoma?
SCROLL
Generally unwell
Orbital pain worsened on pressure
Red and tearing eye
Blurred vision
Haloes around lights
Associated headache, nausea and vomiting
Hazy cornea
Decreased visual acuity
Dilated pupil
Management of acute angle closure glaucoma in the community?
Referred for same day assessment with ophthalmologist form primary care
Lie patient flat without pillow
Give Pilocarpine eye drops
Acetazolamide 500mg PO if available
Analgesia and antiemetics
What does miosis mean?
pupillary contraction.
Mechanism of action of pilocarpine?
Miotic agent - constricts pupils
Ciliary muscle contraction
Both mechanisms open the angle and drain aqueous humour from the eye
Acetazolamide mechanism of action?
Carbonic anhydrase inhibitor - reduces production of aqueous humour production
Management of acute angle closure glaucoma in secondary care?
Definitive treatment: Laser iridotomy
Pilocarpine
Acetazolamide
hyperosmotic agents - e.g. Glycerol or mannitol
Beta blockers - e.g. Timolol - reduces aqueous humour production
Sympathomimetics - reduce aqueous humour production
