Glaucoma Flashcards
What is glaucoma?
A group of eye conditions related to intraocular HTN (increased pressure in the eye) due to blockage in the drainage system of aqueous humour.
This results in damage to the optic nerve –> blindness if left untreated.
What is aqueous humour secreted by?
Ciliary epithelium
What drains the aqueous humour from the eye?
Trabecular meshwork –> it is drained into the canal of schlemm and then the aqueous veins.
Define intraocular pressure
> 21 mmHg (2.8 kPa)
What are the 2 types of glaucoma?
1) Open angle glaucoma
2) Acute angle closure glaucoma
What causes raised intraocular pressure in glaucoma?
Blockage in aqueous humour trying to escape the eye
What is the vitreous chamber of the eye filled with?
Vitreous humour
Where is the anterior chamber of the eye located?
Between the cornea and iris
Where is the posterior chamber of the eye located?
Between the lens and iris
What is the role of the aqueous humour?
Supplies nutrients to the cornea.
Describe route of aqueous humour
1) produced by ciliary body
2) flows through posterior chamber and around the iris to the anterior chamber
3) drains through the trabecular meshwork to the canal of Schlemm
4) From the canal of Schlemm, it eventually enters the general circulation
What is normal intraocular pressure?
10-21 mmHg
What occurs in open angle glaucoma?
There is a GRADUAL increase in resistance to flow through the trabecular meshwork.
The pressure slowly builds within the eye.
How does raised IOP affect the optic disc?
Causes cupping of the optic disc.
What is cupping of the optic disc?
In the centre of the optic disc is an indent called the optic cup.
The optic cup usually is less than 50% of the size of the optic disc.
Raised IOP causes this indent to become wider and deeper, described as “cupping”.
A cup-disk ratio greater than 0.7 is abnormal.
What are some risk factors for open angle glaucoma?
- Increasing age
- Family history
- Black ethnic origin
- Myopia (nearsightedness)
- HTN
- Diabetes
- Steroids
How is open angle glaucoma often diagnosed?
The rise in intraocular pressure may be asymptomatic for a long time and diagnosed by routine eye testing.
What is the most common presenting symptom of open angle glaucoma?
Gradual onset of PERIPHERAL vision loss (tunnel vision).
Give some clinical features of open-angle glaucoma
1) peripheral visual field loss
2) decreased visual acuity (blurred vision)
3) optic disc cupping
4) fluctuating pain
5) headaches
6) halos around lights, particularly at night
Fundoscopy findings in open angle glaucoma?
1) Optic disc cupping (cup to disc ratio >0.7)
2) Optic disc pallor
3) Bayonetting of vessels
What does optic disc pallor indicate in open-angle glaucoma?
Optic atrophy
What is bayonetting of vessels in open-angle glaucoma?
Vessels have breaks as they disappear into the deep cup and re-appear at the base
What investigation is commonly used for estimating IOP by opticians?
Non-contact tonometry
What is involved in non-contact tonometry?
Shooting a “puff of air” at the cornea and measuring the corneal response
What is the gold-standard way to measure IOP?
Goldmann applanation tonometry
It involves a device mounted on a slip lamp that makes contact with the cornea and applies various pressures.
What investigations are involved in diagnosing open angle glaucoma?
1) Goldmann applanation tonometry - for IOP
2) Slit lamp assessment - for the cup-disk ratio and optic nerve health
3) Visual field assessment - for peripheral field loss
4) Gonioscopy - to assess the angle between the iris and cornea
5) Central corneal thickness assessment
At what IOP is treatment for open angle glaucoma typically started?
24mmHg or above
1st line mx of open angle glaucoma?
360° selective laser trabeculoplasty
What is 360° selective laser trabeculoplasty?
During the procedure, a laser is directed at the trabecular meshwork, improving drainage.
It may delay or prevent the need for eye drops. A second procedure may be necessary at a later date.
What is the 1st line MEDICAL mx of open angle glaucoma?
Prostaglandin analogue eye drops (e.g., latanoprost)
Role of prostaglandin analogue eye drops in open angle glaucoma?
These increase uveoscleral outflow
What are 3 notable side effects of prostaglandin analogue eye drops?
1) Eyelash growth
2) Eyelid pigmentation
3) Iris pigmentation (browning)
What are some other eye drop options in open angle glaucoma?
1) Beta-blockers (e.g., timolol)
2) Carbonic anhydrase inhibitors (e.g., dorzolamide)
3) Sympathomimetics (e.g., brimonidine)
What is the role of beta blocker eye drops in open angle glaucoma?
Reduce the production of aqueous humour
What is the role of carbonic anhydrase inhibitors (e.g., dorzolamide) in open angle glaucoma?
reduce the production of aqueous humour
Role of sympathomimetics (e.g., brimonidine) in open angle glaucoma?
Reduce the production of aqueous fluid and increase the uveoscleral outflow
What surgery may be required in refractory cases of open angle glaucoma
Trabeculectomy
This involves creating a new channel from the anterior chamber through the sclera to a location under the conjunctiva, causing a bleb on the conjunctiva. From here, it is reabsorbed into the general circulation.
What happens in acute angle closure glaucoma?
The iris bulges forward and seals off the trabecular meshwork from the anterior chamber.
This prevents aqueous humour from draining. This leads to a continual increase in IOP.
The pressure builds in the posterior chamber, pushing the iris forward and exacerbating the angle closure.
This is an ophthalmological emergency.
What are some risk factors for acute angle-closure glaucoma?
- Increasing age
- Family history
- Female (four times more likely than males)
- Chinese and East Asian ethnic origin
- Shallow anterior chamber
What can trigger AACG in predisposed individuals?
Situations that induce pupil dilation e.g. watching TV in a dark room, medications with mydriatic properties
What are some medications can precipitate AACG?
1) Adrenergic medications (e.g., noradrenaline)
2) Anticholinergic medications (e.g., oxybutynin and solifenacin)
3) TCAs (e.g., amitriptyline), which have anticholinergic effects
Clinical features of AACG?
- Severely painful red eye
- Blurred vision
- Halos around lights
- N&V, headache
Signs on exam in AACG?
- Red eye
- Hazy cornea
- Decreased visual acuity
- Mid-dilated pupil
- Fixed-size pupil
- Hard eyeball on gentle palpation
Pupil dilation in AACG?
A mid-dilated, non-reactive pupil
Investigations in AACG?
1) Visual acuity
2) Pupil assessment
3) Slit-lamp examination
4) IOP (Goldmann applanation tonometry)
5) Gonioscopy
What investigation enables direct view of the iridocorneal angle, allowing assessment of its width and configuration?
Gonioscopy
A closed angle is diagnostic of angle closure glaucoma.
Initial mx of AACG?
Goal is to lower IOP:
1) Lying the patient on their back without a pillow
2) Medical:
- beta blockers e.g. timolol (topical)
- carbonic anhydrase inhibitors: topical (dorzolamide) and oral (acetazolamide)
- systemic mannitol
- pilocarpine eye drops
3) Analgesia and an antiemetic, if required
What is mechanism of acetazolamide?
Carbonic anhydrase inhibitors –> reduces aqueous secretions
Role of IV mannitol in AACG?
IV mannitol rapidly lowers IOP by drawing fluid out of the eye.
What is the definitive treatment of choice in AACG?
Laser peripheral iridotomy (LPI)
What happens in LPI?
A small hole is created in the peripheral iris, allowing the aqueous humour to bypass the blocked area and flow into the anterior chamber.
LPI should be performed as soon as the cornea clears enough for laser application.
Role of pilocarpine in AACG?
This is a direct parasympathomimetic.
It causes contraction of the ciliary muscle –> opening the trabecular meshwork –> increased outflow of the aqueous humour).
