GLAUCOMA Flashcards
What is the main cause of glaucoma?
Increased intraocular pressure
What determines the intraocular pressure?
The balance between the rate of aqueous humour production by the ciliary body and the rate of clearance by the trabecular meshwork.
What are the two main types of primary glaucoma?
Primary open angle glaucoma (POAG)
Primary angle closure glaucoma (PACG)
What is the most common type of primary glaucoma in most races?
Primary open angle glaucoma (POAG)
What is the normal range of intraocular pressure?
10-22 mmHg
What is the mechanism of ganglion cell damage by high intraocular pressure?
Combination of mechanical distortion and localised disturbance of vascular supply.
What is the pattern of damage in term of visual loss?
Sensitivity to light in the periphery is lost first. This is followed by more central vision being affected until the majority is eventually completely lost.
Glaucoma is the most common cause of irreversible blindness
What percentage of the ganglion cells will have been irreversibly damaged before visual field testing will pick up the pathology?
30-50%
What is the main mechanism behind primary open angle glaucoma?
Idiopathic age-related changes to the trabecular meshwork
What group of patients is most commonly affected by open angle glaucoma?
Those of African origin (5 times more likely than caucasian)
What are the risk factors for developing open angle glaucoma?
Older age
Raised IOP
Affected first degree relative
African origin
Myopia
Thin cornea
Larger optic disc
Pupillary dilatation
What is the main symptom for open angle glaucoma?
Progressive visual loss - often found using objective tests rather than patient subjective reporting
What intraocular pressure is typically reached to cause acute angle closure glaucoma?
65 mmHg
What is the instrument used to measure the intraocular pressure?
The Goldmann tonometer
What are the symptoms of acute angle closure glaucoma?
Headache
Severe pain in the eye or over the brow
Photophobia
Loss of vision
Nausea and vomiting
Seeing haloes around lights
Symptoms worse with mydriasis (dilation of the pupil - eg watching TV in dark room)
On examination of someone with acute angle glaucoma, what signs might you expect to pick up?
Severely reduced acuity in the affected eye (often worse than 6/60)
Red eye
Hazy cornea (due to oedema)
Oval pupil
Semi-dilated non reactive pupil
Cupping of the disc (increased cup-to-disc ratio)
What are the risk factors for developing acute angle closure glaucoma?
Elderly Hypermetrope (long sighted) Use of topical steroids (despite being a treatment can raise the IOP)
What is the window of time between extremely elevated intraocular pressure and the retina becoming so ischaemic that it dies?
4 hours
How do you medically treat acute angle closure glaucoma?
- Carbonic anhydrase inhibitor - i.v acetazolamide
- Topical steroids - dexamethasone
- Topical cholinergic (miotics) - pilocarpine
- Topical beta-blockers - timolol, levobunolol
- Topical alpha-adrenergic agonists - brimonidine, apraclonidine
- Carbonic anhydrase inhibitor can be given topically but DO NOT do this if IV has already been given - dorzolamide or brinzolamide
- Topical prostagladin analogues - latanoprost, travoprost
How does the concentration of pilocarpine differ based on the colour of the patient’s iris?
Blue or green - 2%
Brown - 4%
What are the laser procedures that can be done to try and help relieve the pressure caused by acute angle closure glaucoma?
Laser peripheral iridotomy - hole in the iris allows movement between the posterior and anterior chamber
Argon laser iridoplasty - upgrade of laser PI where this time a ring of iris is thinned
Laser trabeculoplasty - directly treats the trabecular meshwork
Trans-scleral diode laser ciliary body ablation - reduced aqueous humour production. Only really used in patients who cannot undergo surgery.
What are the surgical procedures that can be done to try and help relieve the pressure caused by acute angle closure glaucoma?
Trabeculectomy - hole is made through the sclera into the anterior chamber. Tubes may be used to help the drainage through the hole.
What are the medical treatment options for open angle glaucoma?
Prostaglandin analogues (e.g. Latanoprost)
Beta-blockers (e.g. Timolol)
Sympathomimetics (e.g. brimonidine, an alpha2-adrenoceptor agonist) - Reduces aqueous production and increases outflow
Carbonic anhydrase inhibitors (e.g. Dorzolamide) - Reduces aqueous production
Miotics (e.g. pilocarpine, a muscarinic receptor agonist)
What is the first line treatment for open angle glaucoma?
Prostaglandin analogues - latanoprost