Ophthalmology - Acute Angle-Closure Glaucoma, Open Angle Glaucoma Flashcards
Acute Angle-Closure Glaucoma (AACG) - what is glaucoma?
Glaucoma refers to the optic nerve damage that is caused by a significant rise in intraocular pressure
The raised intraocular pressure is caused by a blockage in aqueous humour trying to escape the eye
AACG - what is AACG?
Acute angle-closure glaucoma occurs when the iris bulges forward and seals off the trabecular meshwork from the anterior chamber preventing aqueous humour from being able to drain away
This leads to a continual build-up of pressure in the eye. The pressure builds up particularly in the posterior chamber, which causes pressure behind the iris and worsens the closure of the angle.
AACG - is it an ophthalmological emergency?
It is an ophthalmology emergency
Emergency treatment is required to prevent permanent loss of vision
AACG - what are the risk factors?
The risk factors are slightly different to open-angle glaucoma:
- Increasing age - lens growth associated with age
- Hypermetropia (long-sightedness)
- pupillary dilatation
- Females - 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
AACG - what is hypermetropia?
Hypermetropia is a common problem with the eyes focusing that can affect your vision at all distances, but especially close-up
AACG - what medications can precipitate it?
- Adrenergic medications such as noradrenalin
-
Anticholinergic medications such as oxybutynin and solifenacin
- Tricyclic antidepressants such as amitriptyline, which have anticholinergic effects
AACG - what are the clinical features?
Painful
Red eye
Blurred vision
Haloes around lights
Nausea and Vomiting
AACG - what are the findings you would find on examination?
- Red-eye
- Teary
- Hazy cornea
- Decreased visual acuity
- Dilatation of the affected pupil
- Fixed pupil size
- Firm eyeball on palpation
AACG - initial management?
Life-threatening causes of red eye refer for same-day assessment by an ophthalmologist
Delay in admission, then:
- Lie patient on their back without a pillow
-
Give pilocarpine eye drops (2% for blue, 4% for brown eyes)
- Give acetazolamide 500 mg orally
- Given analgesia and an antiemetic if required
AACG - how does pilocarpine help?
Pilocarpine acts on the muscarinic receptors in the sphincter muscles in the iris and causes constriction of the pupil
Therefore it is a miotic agent
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
OR short hand version
pilocarpine, causes contraction of the ciliary muscle → opening the trabecular meshwork → increased outflow of the aqueous humour
AACG - how does Acetazolamide help?
Acetazolamide is a carbonic anhydrase inhibitor
Reduces the production of aqueous humour
AACG - what two other agents can be used to reduce the production of aqueous humor?
-
Timolol is a beta-blocker that reduces the production of aqueous humour
- Dorzolamide is a carbonic anhydrase inhibitor that reduces the production of aqueous humour
AACG - what is the definitive management?
Laser peripheral iridotomy
Creates a tiny hole in the peripheral iris → aqueous humour flowing to the angle
Open Angle Glaucoma (OAG) - what is it?
Glaucoma refers to optic nerve damage sustained by raised intraocular pressure
The raised intraocular pressure is caused by a blockage in aqueous humour trying to escape the eye
OAG - what is th vitreous chamber filled with?
Vitreous humour
OAG - what is the anterior and posterior chamber filled with?
Aqueous humour
OAG - where does the anterior and posterior chamber lie?
Anterior chamber between the cornea and the iris
Posterior chamber between the lens and the iris
Filled with aqueous humour that supplies nutrients to the cornea
OAG - what is the pathway of aqueous humor flow?
The aqueous humour is produced by the ciliary body
Aqueous humour flows from the ciliary body, around the lens and under the iris, through the anterior chamber, through the trabecular meshwork and into the canal of Schlemm
From the canal of Schlemm it eventually enters the general circulation
OSG - what is the normal intraocular pressure range, and what is the pressure caused by?
The normal intraocular pressure is 10-21 mmHg
Pressure is created by the resistance to flow through the trabecular meshwork into the canal of Schlemm
OAG - pathophysiology?
In open-angle glaucoma, there is a gradual increase in resistance through the trabecular meshwork
So makes it more difficult for aqueous humour to flow through the meshwork and exit the eye
Therefore pressure slowly builds within the eye and this gives a slow and chronic onset of glaucoma
OAG - how is OAG different in terms of length of presentation to AACG?
OAG - pressure slowly builds within the eye and this gives a slow and chronic onset of glaucoma
AACG - the iris bulges forward and seals off the trabecular meshwork from the anterior chamber preventing aqueous humour from being able to drain away, therefore leads to a continual build-up of pressure, acute, and ophthalmology emergency
Picture is for AACG pathophysiology
OAG - how does it cause ‘cupping’ of the optic disc?
Increased pressure in the eye causes cupping of the optic disc
In the centre of a normal optic disc is the optic cup
This is a small indent in the optic disc, it is usually less than half the size of the optic disc
When there is raised intraocular pressure, this indent becomes larger as the pressure in the eye puts pressure on that indent making it wider and deeper
This is called “cupping”
An optic cup greater than 0.5 the size of the optic disc is abnormal
OAG - how to measure intraocular pressure?
Non-contact tonometry - shoots a “puff of air” at the cornea and measuring the corneal response to that air, less accurate
GOLD STANDARD - Goldmann applanation tonometry, involves a special device mounted on a slip lamp that makes contact with the cornea and applies different pressures to the front of the cornea to get an accurate measurement of what the intraocular pressure is
OAG - what surgical management can you do?
Trabeculectomy surgery -required when eye drops ineffective
Creates a new channel from the anterior chamber, through the sclera to a location under the conjunctiva
Causes a “bleb” under the conjunctiva where the aqueous humour drains
Then reabsorbed from this bleb into the general circulation
