Glaucoma Flashcards
What are the two types of glaucoma?
Open angle and closed angle
What is open angle glaucoma?
This is where there is a gradual resistance through the trabecular meshwork.
What are the anatomical landmarks for the anterior and posterior chambers?
The anterior chamber= this is between the cornea and the iris (aqueous humour)
The posterior chamber= between the lens and the iris (vitreous humour)
What is the route of the aqueous humour?
The aqueous humour is produced in the ciliary body and then flows passed the iris and into the anterior chamber and then flows through the trabecular meshwork and into the canal of schlemm, it then enters the general circulation and is reabsorbed into the body.
What is the normal intraocular pressure?
10-21 mmHG (this pressure is created by the resistance to flow through the trabecular meshwork, therefore if there is resistance the intraocular pressure will go up).
What is the pathophysiology behind open angle glaucoma?
This is an increased gradual resistance to trabeculae meshwork, the pressure goes up
What is the structure of the optic disc usually?
Like a bagel so you have the optic disc and the optic cup inside and the optic cup is usually less than half the size of the optic disc.
What happens to the optic cup size in open angle glaucoma?
The cup size increases to more than half the size of the optic disc, this is called cupping.
What are the risk factors for open angle glaucoma?
Increasing age
Family history
Black ethnic origin
Near sightedness (myopia)
What is the presentation of open angle glaucoma?
It is usually asymptomatic
It is routine screening by optometrist
Usually affects peripheral vision first and they will get tunnel vision
Gradual onset of fluctuating pain, headaches, blurred vision, halos surrounding lights which is worse at night
How do we measure intraocular pressure.
Non contact tonometry (machine- shoots a puff of air at the cornea and measuring the corneal response) this is a less accurate way of measuring the intra ocular pressure but it gives an estimate for screening purposes
Goldmann applanation tonometry (GOLD STANDARD) this applies different pressures on the cornea and is the GOlD standard measurement of intra ocular pressure, it actually presses down on the cornea to check how much resistance and how much pressure there is in the cornea.
So overall how is glaucoma diagnosed?
Goldmann applanation tonometry (to measure the Intra ocular pressure)
Fundoscopy to check for cupping
Visual fields to look for peripheral vision loss
How do you manage open angle closure glaucoma? (Medical)
The aim is to decrease the intraocular pressure
It it started at > or equal to 24mmHg
Treatment should be guided by a close follow up of an opthalmologist
First line treatment= eye drops prostaglandin analogues (eg: latanoprost) these eye drops increase the uveoscleral outflow (the drainage of the aqeous humour from the anterior chamber into the anterior chamber outflow
Other options;
Topical beta blockers eg:timolol which decrease the production of aqueous humour
Carbonic anhydrase inhibitors- dorzolamide which decrease the production of aqueous humour
Sympathomimetics- brimonidine
Which decrease the production of aqueous humour and increase uveoscleral outflow
What are the side effects from prostaglandin analogues?
Eyelash growth
Eyelid pigmentation
Iris pigmentation (brown)
What is the surgical option for open angle glaucoma?
Trabebeculectomy
Which involves cresting a new channel from the anterior chamber through the sclera and under the conjunctiva (bleb)
The aqeuous humour then goes from the bleb to the circulation
What is avute angle closure glaucoma?
This is when the iris bulges forward and seals off the trabeculae meshwork from the anterior chamber, preventing aqueous humour from being able to drain away. There is raised intra ocular pressure particularly in the posterior chamber which further compresses the iris
It is an OPTHALMOLOGY EMERGENCY
What are the risk factors for acute angle closure glaucoma?
Increased age Female Family Hx Chinese/east asian ethnic origin Shallow anterior chamber
Certain medications can make you more at risk to acute angle closure glaucoma
Adrenergic medications- noradrenaline
Anticholinergic medications- oxybutynin, solifenacin
TCAS- amitriptylline
What are the risk factors for acute angle closure glaucoma?
Medications
Adrenergi
What is the presentation of acute angle closure glaucoma?
It is a systemic condition so the patient will appear unwell Severely painful red eye Blurred vision Halos around lights Associated headache, nausea and vomiting
What would you find on examination of acute angle closure glaucoma?
Red eye Hazy cornea Pupil dilated and fixed Firm and hard eye on palpation Teary eye Reduced visual acuity
What is the initial management?
Refer for same day assesment by opthalmology
If you are in GP and they are waiting for an ambulance- lie on their back, pilocarpine eye drops, acetazolamide 500mg orally, give analgesia and anti emetics if required
How do pilocarpine eye drops work for acute angle closure glaucoma?
They work by acting on the muscarinic receptors of the sphincter muscles of the iris which causes constriction of the pupil
Pupil constriction is a response of parasympathetic nerve fibres, these release acetylcholine, these are muscarinic receptors. It is a miotic agent.
It also causes ciliary muscle contraction
Both of these actions allows the angle to open and allows better drainage.
How does ACETAZOLAMIDE work?
This is a carbonic anhydrase inhibitor and reduces the production of aqueous humour.
What is the management in secondary care for acute angle closure glaucoma?
Pilocarpine, acetazolamide,
hyperosmotic agents (glycerol, mannitol)
Timolol
Dorzolamide (also a carbonic anhydrase inhibitor)
Brimonidine (sympathomimetic)
Definitive treatment is laser iridotomy (creating a hole in the iris which allows aqeous fluid to flow from the posterior chamber into the anterior chamber)
